anchor
stringlengths 50
3.92k
| positive
stringlengths 55
6.16k
|
|---|---|
The Population of Viscosity- and Gravitational Wave-Driven Supermassive
Black Hole Binaries Among Luminous AGN: Supermassive black hole binaries (SMBHBs) in galactic nuclei are thought to
be a common by-product of major galaxy mergers. We use simple disk models for
the circumbinary gas and for the binary-disk interaction to follow the orbital
decay of SMBHBs with a range of total masses (M) and mass ratios (q), through
physically distinct regions of the disk, until gravitational waves (GWs) take
over their evolution. Prior to the GW-driven phase, the viscous decay is in the
stalled "secondary-dominated" regime. SMBHBs spend a non-negligible fraction of
10^7 years at orbital periods t_var between a day and a year. A dedicated
optical or X-ray survey could identify coalescing SMBHBs statistically, as a
population of periodically variable quasars, whose abundance N_var is
proportional to t_var^alpha, in a range of periods t_var around tens of weeks.
SMBHBs with M < 10^7 M_sun, with 0.5 < alpha < 1.5, would probe the physics of
viscous orbital decay, whereas the detection of a population of higher-mass
binaries, with alpha=8/3, would confirm that their decay is driven by GWs. The
lowest mass SMBHBs (M < 10^{5-6} M_sun) enter the GW-driven regime at short
orbital periods, in the frequency band of the Laser Interferometric Space
Antenna (LISA). While viscous processes are strongly sub-dominant in the last
few years of coalescence, they could reduce the amplitude of any unresolved
background of near-stationary LISA sources. We discuss constraints on the SMBHB
population available from existing data, and the sensitivity and sky coverage
requirements for a detection in future surveys. SMBHBs may also be identified
from velocity shifts in their spectra; we discuss the expected abundance of
SMBHBs as a function of their orbital velocity. | The formation of the first stars and galaxies: Observations made using large ground-based and space-borne telescopes have
probed cosmic history all the way from the present-day to a time when the
Universe was less than a tenth of its present age. Earlier on lies the
remaining frontier, where the first stars, galaxies, and massive black holes
formed. They fundamentally transformed the early Universe by endowing it with
the first sources of light and chemical elements beyond the primordial hydrogen
and helium produced in the Big Bang. The interplay of theory and upcoming
observations promises to answer the key open questions in this emerging field. |
The State of the Warm and Cold Gas in the Extreme Starburst at the Core
of the Phoenix Galaxy Cluster (SPT-CLJ2344-4243): [Abridged] We present new optical integral field spectroscopy (Gemini South)
and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in
the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to
have a massive starburst (~800 Msun/yr) in the central, brightest cluster
galaxy, most likely fueled by the rapidly-cooling intracluster medium. These
new data reveal a complex emission-line nebula, extending for >30 kpc from the
central galaxy. The total Halpha luminosity, assuming Halpha/Hbeta = 2.85, is
L_Ha = 7.6 +/- 0.4 x10^43 erg/s, making this the most luminous emission line
nebula detected in the center of a cool core cluster. Overall, the relative
fluxes of the low-ionization lines (e.g., [O II], Hbeta) to the UV continuum
are consistent with photoionization by young stars. In both the center of the
galaxy and in a newly-discovered highly-ionized plume to the north of the
galaxy, the ionization ratios are consistent with both shocks and AGN
photoionization. We speculate that this extended plume may be a galactic wind,
driven and partially photoionized by both the starburst and central AGN. We
find evidence for shocks throughout the ISM of the central galaxy, most likely
driven by a combination of stellar winds from massive young stars,
core-collapse supernovae, and the central AGN. In addition to the warm, ionized
gas, we detect a substantial amount of cold, molecular gas via the CO(3-2)
transition, coincident in position with the galaxy center. We infer a molecular
gas mass of M_H2 = 2.2 +/- 0.6 x10^10 Msun, which implies that the starburst
will consume its fuel in ~30 Myr if it is not replenished. The combination of
the high level of turbulence in the warm phase and the high L_IR/M_H2 ratio
suggests that this violent starburst may be in the process of quenching itself. | On the Possibility of Detecting a Global Signal in the Line of the
Hyperfine Structure of Hydrogen from the Dark Ages: We analyze the possibilities of detecting a signal in the hydrogen 21~cm
line, which was formed in the early Universe during the the Dark Ages
cosmological epoch, using the Ukrainian radio telescopes UTR-2 and GURT of the
National Academy of Sciences of Ukraine. As a result of cosmological expansion,
this line is shifted to the decameter range of wavelengths
($\lambda_{obs}\approx18$ m, $\nu_{obs}\approx16$ MHz) and is in the band of
operational frequencies of these telescopes. The brightness temperature of the
predicted sky-averaged global signal ranges from $\sim-0.08$ to $\sim0.02$ K,
depending on the cosmological model. Such a faint signal is a challenge even
for the world's largest radio telescope in the decameter wavelength range,
UTR-2, since the signal level of the foreground synchrotron radiation of the
Galaxy at these wavelengths is 20000--40000~K. The paper highlights the
peculiarities of spectroscopy at the decameter waves, interfering factors of
natural and instrumental origin and the ways of eliminating them in order to
reliably detect the signal in the 21~cm line, which can become an important
source of information both about the environment in which the first stars and
galaxies were born, and about the nature of dark matter particles and the
magnitude of primordial magnetic fields. It was concluded that the detection of
such a signal using the most sensitive radio telescopes at the decameter
wavelength range is possible (with the signal integration over the frequency
band of 25~MHz), the detection time will be $\sim50$~days) and can be
implemented in the coming years of peace in Ukraine. |
Probing the Small Scale Matter Power Spectrum through Dark Matter
Annihilation in the Early Universe: Recent observations of the cosmic microwave background (CMB) anisotropies and
the distribution of galaxies, galaxy clusters, and the Lyman Alpha forest have
constrained the shape of the power spectrum of matter fluctuations on large
scales k < few h/Mpc. We explore a new technique to constrain the matter power
spectrum on smaller scales, assuming the dark matter is a Weakly Interacting
Massive Particle (WIMP) that annihilates at early epochs. Energy released by
dark matter annihilation can modify the spectrum of CMB temperature
fluctuations and thus CMB experiments such as Planck have been able to
constrain the quantity f <sigma v> /m < 1/88 picobarn c / GeV, where f is the
fraction of energy absorbed by gas, <sigma v> is the annihilation rate assumed
constant, and m is the particle mass. We assume the standard scale-invariant
primordial matter power spectrum of P_prim(k) ~ k^{n_s} at large scales k <
k_p, while we adopt the modified power law of P_prim(k) ~ k_p^{n_s}
(k/k_p)^{m_s} at small scales. We then aim at deriving constraints on m_s. For
m_s > n_s, the excess small-scale power results in a much larger number of
nonlinear small mass halos, particularly at high redshifts. Dark matter
annihilation in these halos releases sufficient energy to partially ionize the
gas, and consequently modify the spectrum of CMB fluctuations. We show that the
recent Planck data can already be used to constrain the power spectrum on small
scales. For a simple model with an NFW profile with halo concentration
parameter c_200 = 5 and f <sigma v> / m = 1/100 picobarn c / GeV, we can limit
the mass variance sigma_{max} < 100 at the 95% confidence level, corresponding
to a power law index m_s < 1.43 (1.63) for k_p = 100 (1000) h/Mpc. Our results
are also relevant to theories that feature a running spectral index. | Interacting dark energy with time varying equation of state and the
$H_0$ tension: Almost in all interacting dark energy models present in the literature, the
stability of the model becomes potentially sensitive to the dark energy
equation of state parameter $w_x$, and a singularity arises at `$w_x = -1$'.
Thus, it becomes mandatory to test the stability of the model into two separate
regions, namely, for quintessence and phantom. This essentially brings in a
discontinuity into the parameters space for $w_x$. Such discontinuity can be
removed with some specific choices of the interaction or coupling function. In
the present work we choose one particular coupling between dark matter and dark
energy which can successfully remove such instability and we allow a dynamical
dark energy equation of state parameter instead of the constant one. In
particular, considering a dynamical dark energy equation of state with only one
free parameter $w_0$, representing the current value of the dark energy
equation of state, we confront the interacting scenario with several
observational datasets. The results show that the present cosmological data
allow an interaction in the dark sector, in agreement with some latest claims
by several authors, and additionally, a phantom behaviour in the dark energy
equation of state is suggested at present. Moreover, for this case the tension
on $H_0$ is clearly released. As a final remark, we mention that according to
the Bayesian analysis, $\Lambda$-cold dark matter ($\Lambda$CDM) is always
favored over this interacting dark energy model. |
Galaxies undergoing ram-pressure stripping: the influence of the bulge
on morphology and star formation rate: We investigate the influence of stellar bulges on the star formation and
morphology of disc galaxies that suffer from ram pressure. Several tree-SPH
(smoothed particle hydrodynamics) simulations have been carried out to study
the dependence of the star formation rate on the mass and size of a stellar
bulge. In addition, different strengths of ram pressure and different
alignments of the disc with respect to the intra-cluster medium (ICM) are
applied. As claimed in previous works, when ram pressure is acting on a galaxy,
the star formation rate (SFR) is enhanced and rises up to four times with
increasing ICM density compared to galaxies that evolve in isolation. However,
a bulge suppresses the SFR when the same ram pressure is applied. Consequently,
fewer new stars are formed because the SFR can be lowered by up to 2 M_sun/yr.
Furthermore, the denser the surrounding gas, the more inter-stellar medium
(ISM) is stripped. While at an ICM density of 10^-28 g/cm^3 about 30% of the
ISM is stripped, the galaxy is almost completely (more than 90%) stripped when
an ICM density of 10^-27 g/cm^3 is applied. But again, a bulge prevents the
stripping of the ISM and reduces the amount being stripped by up to 10%.
Thereby, fewer stars are formed in the wake if the galaxy contains a bulge. The
dependence of the SFR on the disc tilt angle is not very pronounced. Hereby a
slight trend of decreasing star formation with increasing inclination angle can
be determined. Furthermore, with increasing disc tilt angles, less gas is
stripped and therefore fewer stars are formed in the wake. Reducing the disc
gas mass fraction results in a lower SFR when the galaxies evolve in vacuum. On
the other hand, the enhancement of the SFR in case of acting ram pressure is
less pronounced with increasing gas mass fraction. Moreover, the fractional
amount of stripped gas does not depend on the gas mass fraction. | 21cmfish: Fisher-matrix framework for fast parameter forecasts from the
cosmic 21-cm signal: The 21-cm signal from neutral hydrogen in the early universe will provide
unprecedented information about the first stars and galaxies. Extracting this
information, however, requires accounting for many unknown astrophysical
processes. Semi-numerical simulations are key for exploring the vast parameter
space of said processes. These simulations use approximate techniques such as
excursion-set and perturbation theory to model the 3D evolution of the
intergalactic medium, at a fraction of the computational cost of hydrodynamic
and/or radiative transfer simulations. However, exploring the enormous
parameter space of the first galaxies can still be computationally expensive.
Here we introduce 21cmfish, a Fisher-matrix wrapper for the semi-numerical
simulation 21cmFAST. 21cmfish facilitates efficient parameter forecasts,
scaling to significantly higher dimensionalities than MCMC approaches, assuming
a multi-variate Gaussian posterior. Our method produces comparable parameter
uncertainty forecasts to previous MCMC analyses but requires ~10$^4$x fewer
simulations. This enables a rapid way to prototype analyses adding new physics
and/or additional parameters. We carry out a forecast for HERA using the
largest astrophysical parameter space to-date, with 10 free parameters,
spanning both population II and III star formation. We find X-ray parameters
for the first galaxies could be measured to sub-percent precision, and, though
they are highly degenerate, the stellar-to-halo mass relation and ionizing
photon escape fraction for population II and III galaxies can be constrained to
~10% precision (logarithmic quantities). Using a principal component analysis
we find HERA is most sensitive to the product of the ionizing escape fraction
and the stellar-to-halo mass fraction for population II galaxies. |
The Linearity of the Cosmic Expansion Field from 300 to 30,000 km/s and
the Bulk Motion of the Local Supercluster with Respect to the CMB: The meaning of "linear expansion" is explained. Particularly accurate
relative distances are compiled and homogenized a) for 246 SNe Ia and 35
clusters with v<30,000 km/s, and b) for relatively nearby galaxies with 176
TRGB and 30 Cepheid distances. The 487 objects define a tight Hubble diagram
from 300-30,000 km/s implying individual distance errors of <7.5%. Here the
velocities are corrected for Virgocentric steaming (locally 220 km/s) and - if
v_220>3500 km/s - for a 495 km/s motion of the Local Supercluster towards the
warm CMB pole at l=275, b=12; local peculiar motions are averaged out by large
numbers. A test for linear expansion shows that the corrected velocities
increase with distance as predicted by a standard model with q_0=-0.55
[corresponding to (Omega_M, Omega_Lambda)=(0.3,0.7)], but the same holds - due
to the distance limitation of the present sample - for a range of models with
q_0 between ~0.00 and -1.00. For these models H_0 does not vary systematically
by more than +/-2.3% over the entire range. Local, distance-dependent
variations are equally limited to 2.3% on average. In particular the proposed
Hubble Bubble of Zehavi et al. and Jha et al. is rejected at the 4sigma level.
- Velocity residuals in function of the angle from the CMB pole yield a
satisfactory apex velocity of 448+/-73 km/s and a coherence radius of the Local
Supercluster of ~3500 km/s (~56 Mpc), beyond which galaxies are seen on average
at rest in co-moving coordinates with respect to the CMB. Since no obvious
single accelerator of the Local Supercluster exists in the direction of the CMB
dipole its motion must be due to the integral gravitational force of all
surrounding structures. Most of the gravitational dipole comes probably from
within 5000 km/s. | Simulations and observational tests of primordial magnetic fields from
Cosmic Microwave Background constraints: We present the first cosmological simulations of primordial magnetic fields
derived from the constraints by the Cosmic Microwave Background observations,
based on the fields' gravitational effect on cosmological perturbations. We
evolved different primordial magnetic field models with the {\enzo} code and
compared their observable signatures (and relative differences) in galaxy
clusters, filaments and voids. The differences in synchrotron radio powers and
Faraday Rotation measure from galaxy clusters are generally too small to be
detected, whereas differences present in filaments will be testable with the
higher sensitivity of the Square Kilometre Array. However, several statistical
full-sky analyses, such as the cross-correlation between galaxies and diffuse
synchrotron power, the Faraday Rotation structure functions from background
radio galaxies, or the analysis of arrival direction of Ultra-High-Energy
Cosmic Rays, can already be used to constrain these primordial field models. |
Disk, merger, or outflow ? Molecular gas kinematics in two powerful
obscured QSOs at z>3.4: We report on the detection of bright CO(4-3) line emission in two powerful,
obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at
z>3.4. We analyze the line strength and profile to determine the gas mass,
dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have
found the first evidence for a molecular, AGN-driven wind in the early
Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and
blueshifted by -200 km/s relative to systemic (where the systemic velocity is
estimated from the narrow components of ionized gas lines, as is commonly done
for AGN at low and high redshifts). SW022550 has a more regular, double-peaked
profile, which is marginally spatially resolved in our data, consistent with
either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun,
are large and account for <30% of the stellar mass, making these obscured QSOs
as gas rich as other powerful CO emitting galaxies at high redshift, i.e.,
submillimeter galaxies. Our sources exhibit relatively lower star-formation
efficiencies compared to other dusty, powerful starburst galaxies at high
redshift. We speculate that this could be a consequence of the AGN perturbing
the molecular gas. | Constraining primordial non-Gaussianity using Neural Networks: We present a novel approach to estimate the value of primordial
non-Gaussianity ($f_{\rm NL}$) parameter directly from the Cosmic Microwave
Background (CMB) maps using a convolutional neural network (CNN). While
traditional methods rely on complex statistical techniques, this study proposes
a simpler approach that employs a neural network to estimate $f_{\rm NL}$. The
neural network model is trained on simulated CMB maps with known $f_{\rm NL}$
in range of $[-50,50]$, and its performance is evaluated using various metrics.
The results indicate that the proposed approach can accurately estimate $f_{\rm
NL}$ values from CMB maps with a significant reduction in complexity compared
to traditional methods. With $500$ validation data, the $f^{\rm output}_{\rm
NL}$ against $f^{\rm input}_{\rm NL}$ graph can be fitted as $y=ax+b$, where
$a=0.980^{+0.098}_{-0.102}$ and $b=0.277^{+0.098}_{-0.101}$, indicating the
unbiasedness of the primordial non-Gaussianity estimation. The results indicate
that the CNN technique can be widely applied to other cosmological parameter
estimation directly from CMB images. |
Environmental Dependence of Type Ia Supernova Luminosities from the
YONSEI Supernova Catalog: There is growing evidence for the dependence of Type Ia supernova (SN Ia)
luminosities on their environments. While the impact of this trend on
estimating cosmological parameters is widely acknowledged, the origin of this
correlation is still under debate. In order to explore this problem, we first
construct the YONSEI (YOnsei Nearby Supernova Evolution Investigation) SN
catalog. The catalog consists of 1231 spectroscopically confirmed SNe Ia over a
wide redshift range (0.01 < z < 1.37) from various SN surveys and includes the
light-curve fit data from two independent light-curve fitters of SALT2 and
MLCS2k2. For a sample of 674 host galaxies, we use the stellar mass and the
star formation rate data in Kim et al. (2018). We find that SNe Ia in low-mass
and star-forming host galaxies are $0.062\pm0.009$ mag and $0.057\pm0.010$ mag
fainter than those in high-mass and passive hosts, after light-curve
corrections with SALT2 and MLCS2k2, respectively. When only local environments
of SNe Ia (e.g., locally star-forming and locally passive) are considered, this
luminosity difference increases to $0.081\pm0.018$ mag for SALT2 and
$0.072\pm0.018$ mag for MLCS2k2. Considering the significant difference in the
mean stellar population age between the two environments, this result suggests
that the origin of environmental dependence is most likely the luminosity
evolution of SNe Ia with redshift. | Star formation at z=1.47 from HiZELS: An Hα+[OII] double-blind
study: This paper presents the results from the first wide and deep dual narrow-band
survey to select H-alpha (Ha) and [OII] line emitters at z=1.47+-0.02 (using
matched narrow-band filters in the H and z' bands), exploiting synergies
between the UKIRT and Subaru telescopes. The Ha survey at z=1.47 reaches a flux
limit of ~7x10^-17 erg/s/cm^2 and detects ~200 Ha emitters over 0.7deg^2, while
the much deeper [OII] survey reaches an effective flux of ~7x10^-18 erg/s/cm^2,
detecting ~1400 z=1.47 [OII] emitters in a matched co-moving volume of
~2.5x10^5 Mpc^3. The combined survey results in the identification of 190
simultaneous Ha and [OII] emitters at z=1.47. Ha and [OII] luminosity functions
are derived and both are shown to evolve significantly from z~0 in a consistent
way. The star formation rate density of the Universe at z=1.47 is evaluated,
with the Ha analysis yielding 0.16+-0.05 M_sun/yr/Mpc^3 and the [OII] analysis
0.17+-0.04 M_sun/yr/Mpc^3. The measurements are combined with other studies,
providing a self-consistent measurement of the star formation history of the
Universe over the last ~11Gyrs. By using a large comparison sample at z~0.1
(from the SDSS), [OII]/Ha line ratios are calibrated as probes of
dust-extinction. Ha emitters at z~1.47 show on average 1 mag of extinction at
Ha, similar to the SDSS sources at z~0. Although we find that dust extinction
correlates with SFR, the relation evolves by about ~0.5 mag from z~1.5 to z~0,
with z~0 relations over-predicting the dust extinction corrections at high-z by
that amount. Stellar mass is found to be a much more fundamental extinction
predictor, with the relation between mass and extinction being valid at both
z~0 and z~1.5. Dust extinction corrections as a function of optical colours are
also derived, offering simpler mechanisms for estimating extinction in
moderately star-forming systems over the last ~9Gyrs [Abridged]. |
Physical conditions in the gas phases of the giant HII region LMC-N11
unveiled by Herschel - I. Diffuse [CII] and [OIII] emission in LMC-N11B: (Abridged) The Magellanic Clouds provide a nearby laboratory for metal-poor
dwarf galaxies. The low dust abundance enhances the penetration of UV photons
into the interstellar medium (ISM), resulting in a relatively larger filling
factor of the ionized gas. Furthermore, there is likely a hidden molecular gas
reservoir probed by the [CII]157um line. We present Herschel/PACS maps in
several tracers, [CII], [OI]63um,145um, [NII]122um, [NIII]57um, and [OIII]88um
in the HII region N11B in the Large Magellanic Cloud. Halpha and [OIII]5007A
images were used as complementary data to investigate the effect of dust
extinction. Observations were interpreted with photoionization models to infer
the gas conditions and estimate the ionized gas contribution to the [CII]
emission. Photodissociation regions (PDRs) are probed through polycyclic
aromatic hydrocarbons (PAHs). We first study the distribution and properties of
the ionized gas. We then constrain the origin of [CII]157um by comparing to
tracers of the low-excitation ionized gas and of PDRs. [OIII] is dominated by
extended emission from the high-excitation diffuse ionized gas; it is the
brightest far-infrared line, ~4 times brighter than [CII]. The extent of the
[OIII] emission suggests that the medium is rather fragmented, allowing far-UV
photons to permeate into the ISM to scales of >30pc. Furthermore, by comparing
[CII] with [NII], we find that 95% of [CII] arises in PDRs, except toward the
stellar cluster for which as much as 15% could arise in the ionized gas. We
find a remarkable correlation between [CII]+[OI] and PAH emission, with [CII]
dominating the cooling in diffuse PDRs and [OI] dominating in the densest PDRs.
The combination of [CII] and [OI] provides a proxy for the total gas cooling in
PDRs. Our results suggest that PAH emission describes better the PDR gas
heating as compared to the total infrared emission. | Mass function of galaxy clusters in relativistic inhomogeneous cosmology: The current cosmological model ($\Lambda$CDM) with the underlying FLRW metric
relies on the assumption of local isotropy, hence homogeneity of the Universe.
Difficulties arise when one attempts to justify this model as an average
description of the Universe from first principles of general relativity, since
in general, the Einstein tensor built from the averaged metric is not equal to
the averaged stress--energy tensor. In this context, the discrepancy between
these quantities is called "cosmological backreaction" and has been the subject
of scientific debate among cosmologists and relativists for more than $20$
years. Here we present one of the methods to tackle this problem, i.e.
averaging the scalar parts of the Einstein equations, together with its
application, the cosmological mass function of galaxy clusters. |
Revealing a Ring-like Cluster Complex in a Tidal Tail of the Starburst
Galaxy NGC 2146: We report the discovery of a ring-like cluster complex in the starburst
galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear
ring-like distribution of star clusters around a central object. It is located
in one of the tidal streams which surround the galaxy. NGC 2146 is part of the
Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data has added
critical information to the available archival Hubble Space Telescope imaging
set of NGC 2146, allowing us to determine ages, masses, and extinctions of the
clusters in the Ruby Ring. These properties have then been used to investigate
the formation of this extraordinary system. We find evidence of a spatial and
temporal correlation between the central cluster and the clusters in the ring.
The latter are about 4 Myr younger than the central cluster, which has an age
of 7 Myr. This result is supported by the H alpha emission which is strongly
coincident with the ring, and weaker at the position of the central cluster.
From the derived total H alpha luminosity of the system we constrain the star
formation rate density to be quite high, e.g. ~ 0.47 Msun/yr/kpc^2. The Ruby
Ring is the product of an intense and localised burst of star formation,
similar to the extended cluster complexes observed in M51 and the Antennae, but
more impressive because is quite isolated. The central cluster contains only 5
% of the total stellar mass in the clusters that are determined within the
complex. The ring-like morphology, the age spread, and the mass ratio support a
triggering formation scenario for this complex. We discuss the formation of the
Ruby Ring in a "collect & collapse" framework. The predictions made by this
model agree quite well with the estimated bubble radius and expansion velocity
produced by the feedback from the central cluster, making the Ruby Ring an
interesting case of triggered star formation. | Characterizing SL2S galaxy groups using the Einstein radius: We analyzed the Einstein radius, $\theta_E$, in our sample of SL2S galaxy
groups, and compared it with $R_A$ (the distance from the arcs to the center of
the lens), using three different approaches: 1.- the velocity dispersion
obtained from weak lensing assuming a Singular Isothermal Sphere profile
($\theta_{E,I}$), 2.- a strong lensing analytical method ($\theta_{E,II}$)
combined with a velocity dispersion-concentration relation derived from
numerical simulations designed to mimic our group sample, 3.- strong lensing
modeling ($\theta_{E,III}$) of eleven groups (with four new models presented in
this work) using HST and CFHT images. Finally, $R_A$ was analyzed as a function
of redshift $z$ to investigate possible correlations with L, N, and the
richness-to-luminosity ratio (N/L). We found a correlation between $\theta_{E}$
and $R_A$, but with large scatter. We estimate $\theta_{E,I}$ = (2.2 $\pm$ 0.9)
+ (0.7 $\pm$ 0.2)$R_A$, $\theta_{E,II}$ = (0.4 $\pm$ 1.5) + (1.1 $\pm$
0.4)$R_A$, and $\theta_{E,III}$ = (0.4 $\pm$ 1.5) + (0.9 $\pm$ 0.3)$R_A$ for
each method respectively. We found a weak evidence of anti-correlation between
$R_A$ and $z$, with Log$R_A$ = (0.58$\pm$0.06) - (0.04$\pm$0.1)$z$, suggesting
a possible evolution of the Einstein radius with $z$, as reported previously by
other authors. Our results also show that $R_A$ is correlated with L and N
(more luminous and richer groups have greater $R_A$), and a possible
correlation between $R_A$ and the N/L ratio. Our analysis indicates that $R_A$
is correlated with $\theta_E$ in our sample, making $R_A$ useful to
characterize properties like L and N (and possible N/L) in galaxy groups.
Additionally, we present evidence suggesting that the Einstein radius evolves
with $z$. |
CFHTLenS: The Canada-France-Hawaii Telescope Lensing Survey: We present the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) that
accurately determines a weak gravitational lensing signal from the full 154
square degrees of deep multi-colour data obtained by the CFHT Legacy Survey.
Weak gravitational lensing by large-scale structure is widely recognised as one
of the most powerful but technically challenging probes of cosmology. We
outline the CFHTLenS analysis pipeline, describing how and why every step of
the chain from the raw pixel data to the lensing shear and photometric redshift
measurement has been revised and improved compared to previous analyses of a
subset of the same data. We present a novel method to identify data which
contributes a non-negligible contamination to our sample and quantify the
required level of calibration for the survey. Through a series of
cosmology-insensitive tests we demonstrate the robustness of the resulting
cosmic shear signal, presenting a science-ready shear and photometric redshift
catalogue for future exploitation. | Primordial Black Holes as a dark matter candidate -- a brief overview: Historically the most popular dark matter candidates have been new elementary
particles, such as Weakly Interacting Massive Particles and axions. However
Primordial Black Holes (PBHs), black holes formed from overdensities in the
early Universe, are another possibility. The discovery of gravitational waves
from mergers of tens of Solar mass black hole binaries by LIGO-Virgo has
generated a surge in interest in PBH dark matter. We overview the formation of
PBHs, observational probes of their abundance, and some of the key open
questions in the field. |
The luminosity-volume method : Derivation of the cosmological number
density in depth from V/Vm distribution [Number density in depth from
luminosity-volume]: The classical cosmological V/Vm-test is introduced and elaborated. Use of the
differential distribution p(V/Vm) of the V/Vm-variable rather than just the
mean <V/Vm> leads directly to the cosmological number density without any need
for assumptions about the cosmological evolution of the underlying (quasar)
population. Calculation of this number density n(z) from p(V/Vm) is illustrated
using the best sample that was available in 1981, when this method was
developed. This sample of 76 quasars is clearly too small for any meaningful
results. The method will be later applied to a much larger cosmological sample
to infer the cosmological number density n(z) as a function of the depth z.
Keywords: V/Vm . luminosity volume . cosmological number density . V/Vm
distribution | Weak Primordial Magnetic Fields and Anisotropies in the Cosmic Microwave
Background Radiation: It is shown that small-scale magnetic fields present before recombination
induce baryonic density inhomogeneities of appreciable magnitude. The presence
of such inhomogeneities changes the ionization history of the Universe, which
in turn decreases the angular scale of the Doppler peaks and increases Silk
damping by photon diffusion. This unique signature could be used to (dis)prove
the existence of primordial magnetic fields of strength as small as B~10^(-11)
Gauss by upcoming cosmic microwave background observations. |
A search for nontoroidal topological lensing in the Sloan Digital Sky
Survey quasar catalog: Flat space models with multiply connected topology, which have compact
dimensions, are tested against the distribution of high-redshift ($z \geq 4$)
quasars of the Sloan Digital Sky Survey (SDSS). When the compact dimensions are
smaller in size than the observed universe, topological lensing occurs, in
which multiple images of single objects (ghost images) are observed. We improve
on the recently introduced method to identify ghost images by means of
four-point statistics. Our method is valid for any of the 17 multiply connected
flat models, including nontoroial ones that are compactified by screw motions
or glide reflection. Applying the method to the data revealed one possible case
of topological lensing caused by sixth-turn screw motion, however, it is
consistent with the simply connected model by this test alone. Moreover,
simulations suggest that we cannot exclude the other space models despite the
absence of their signatures. This uncertainty mainly originates from the patchy
coverage of SDSS in the South Galactic cap, and the situation will be improved
by future wide-field spectroscopic surveys. | The dynamical intracluster medium: a combined approach of observations
and simulations: Current high resolution observations of galaxy clusters reveal a dynamical
intracluster medium (ICM). The wealth of structures includes signatures of
interactions between active galactic nuclei (AGN) and the ICM, such as cavities
and shocks, as well as signatures of bulk motions, e.g. cold fronts. Aiming at
understanding the physics of the ICM, we study individual clusters by both,
deep high resolution observations and numerical simulations which include
processes suspected to be at work, and aim at reproducing the observed
properties. By comparing observations and simulations in detail, we gain deeper
insights into cluster properties and processes. Here we present two examples of
our approach: the large-scale shock in the Hydra A cluster, and sloshing cold
fronts. |
The interacting vacuum and tensions: a comparison of theoretical models: We analyse three interacting vacuum dark energy models with the aim of
exploring whether the $H_0$ and $\sigma_8$ tensions can be simultaneously
resolved in such models. We present the first ever derivation of the covariant
gauge-invariant perturbation formalism for the interacting vacuum scenario,
and, for the sub-class of geodesic cold dark matter models, connect the
evolution of perturbation variables in this approach to the familiar
cosmological observables. We show how $H_0$ and $\sigma_8$ evolve in three
interacting vacuum models: firstly, a simple linear coupling between the vacuum
and cold dark matter; secondly, a coupling which mimics the behaviour of a
Chaplygin gas; and finally a coupling which mimics the Shan--Chen fluid dark
energy model. We identify, if any, the regions of parameter space which would
correspond to a simultaneous resolution of both tensions in these models. When
constraints from observational data are added, we show how all the models
described are constrained to be close to their $\Lambda$CDM limits. | Where are the Luminous Red Galaxies (LRGs)? Using correlation
measurements and lensing to relate LRGs to dark matter halos: Nonlinear redshift-space distortions, the Finger-of-God (FoG) effect, can
complicate the interpretation of the galaxy power spectrum. Here, we
demonstrate the method proposed by Hikage et al. (2012) to use complimentary
observations to directly constrain this effect on the data. We use catalogs of
Luminous Red Galaxies (LRGs) and photometric galaxies from the SDSS DR7 to
measure the redshift-space power spectrum of LRGs, the cross-correlation of
LRGs with the shapes of background photometric galaxies (galaxy-galaxy weak
lensing), and the projected cross-correlation of LRGs with photometric galaxies
having similar photometric redshifts to the LRG spectroscopic redshift. All of
these measurements use a reconstructed halo field. While we use the position of
each LRG for single LRG systems, we compare the measurements using different
halo-center proxies for multiple-LRG systems (4.5 per cent of all the halos):
the brightest LRG position (BLRG), the faintest LRG position (FLRG) and their
arithmetical mean position (Mean), respectively, in each system. We find
significant differences in the measured correlations of different centers,
showing consistent off-centering effects in the three observables. By comparing
the measurements with a halo model that treats the satellite photometric
galaxies as being distributed according to a generalized NFW profile, we find
that about 40 (70) per cent of BLRGs (FLRGs) are off-centered satellite
galaxies in the multiple-LRG systems. The satellite LRGs have typical
off-centering radius of about 400 kpc/h, and velocity dispersion of about 500
km/s in host halos with a mean mass of 1.6x10^14 Ms/h. We show that, if LRGs in
the single LRG systems have similar offsets, the residual FoG contamination in
the LRG power spectrum can be significant at k>0.1 h/Mpc, which may cause a
bias in cosmological parameters such as the neutrino mass. |
Model-independent X-ray mass determinations: A new method is introduced for making X-ray mass determinations of spherical
clusters of galaxies. Treating the distribution of gravitating matter as
piecewise constant and the cluster atmosphere as piecewise isothermal, X-ray
spectra of a hydrostatic atmosphere are determined up to a single overall
normalizing factor. In contrast to more conventional approaches, this method
relies on the minimum of assumptions, apart from the conditions of hydrostatic
equilibrium and spherical symmetry. The method has been implemented as an XSPEC
mixing model called CLMASS, which was used to determine masses for a sample of
nine relaxed X-ray clusters. Compared to conventional mass determinations,
CLMASS provides weak constraints on values of M_500, reflecting the quality of
current X-ray data for cluster regions beyond r_500. At smaller radii, where
there are high quality X-ray spectra inside and outside the radius of interest
to constrain the mass, CLMASS gives confidence ranges for M_2500 that are only
moderately less restrictive than those from more familiar mass determination
methods. The CLMASS model provides some advantages over other methods and
should prove useful for mass determinations in regions where there are high
quality X-ray data. | A large 12C/13C isotopic ratio in M82 and NGC253: To derive carbon isotopic ratios from optically thin tracers in the central
regions of the starburst galaxies M82 and NGC253. We present high sensitivity
observations of CCH and two of its 13C isotopologues, C13CH and 13CCH, as well
as the optically thin emission from C18O and 13C18O. We assume the column
density ratio between isotopologues is representative of the 12C13C isotopic
ratio. From CCH, lower limits to the 12C/13C isotopic ratio of 138 in M82, and
81 in NGC253, are derived. Lower limits to the 12C/13C ratios from CO
isotopologues support these. 13C18O is tentatively detected in NGC253, which is
the first reported detection in the extragalactic ISM. Based on these limits,
we infer ratios of 16O/18O>350 and >300 in M82 and NGC253, respectively, and
32S/34S>16 in NGC253. and the H2 column density determination through the
optically thin tracers 13CO and C18O. The derived CCH fractional abundances
toward these galaxies of <~1.1\times10^-8 are in good agreement with those of
molecular clouds in the Galactic disk. Our lower limits to the 12C/13C ratio
from CCH are a factor of 2-3 larger than previous limits. The results are
discussed in the context of molecular and nucleo-chemical evolution. The large
12C/13C isotopic ratio of the molecular ISM in these starburst galaxies suggest
that the gas has been recently accreted toward their nuclear regions. |
Scanning For Dark Matter Subhalos in Hubble Space Telescope Imaging of
54 Strong Lenses: The cold dark matter (DM) model predicts that every galaxy contains thousands
of DM subhalos; almost all other DM models include a physical process that
smooths away the subhalos. The subhalos are invisible, but could be detected
via strong gravitational lensing, if they lie on the line of sight to a
multiply-imaged background source, and perturb its apparent shape. We present a
predominantly automated strong lens analysis framework, and scan for DM
subhalos in Hubble Space Telescope imaging of 54 strong lenses. We identify
five DM subhalo candidates, including two especially compelling candidates (one
previously known in SLACS0946+1006) where a subhalo is favoured after all of
our tests for systematics. We find that the detectability of subhalos depends
upon the assumed parametric form for the lens galaxy's mass distribution,
especially its degree of azimuthal freedom. Using separate components for dark
matter and stellar mass reveals two DM subhalo candidates and removes four
false-positives compared to the single power-law mass model that is common in
the literature. We identify 45 lenses without substructures, the number of
which is key to statistical tests able to rule out models of e.g. warm or
self-interacting DM. Our full analysis results are available at
https://github.com/Jammy2211/autolens_subhalo. | The Surprising Absence of Absorption in the Far-Ultraviolet Spectrum of
Mrk 231: Mrk 231, the nearest (z = 0.0422) quasar, hosts both a galactic-scale wind
and a nuclear-scale iron low-ionization broad absorption line (FeLoBAL)
outflow. We recently obtained a far-ultraviolet (FUV) spectrum of this object
covering ~1150 - 1470 A with the Cosmic Origins Spectrograph on board the
Hubble Space Telescope. This spectrum is highly peculiar, highlighted by the
presence of faint (~< 2% of predictions based on H-alpha), broad (>~ 10,000
km/s at the base), and highly blueshifted (centroid at ~ -3500 km/s) Ly-alpha
emission. The FUV continuum emission is slightly declining at shorter
wavelengths (consistent with F_lambda ~ lambda^1.7) and does not show the
presence of any obvious photospheric or wind stellar features. Surprisingly,
the FUV spectrum also does not show any unambiguous broad absorption features.
It thus appears to be dominated by the AGN, rather than hot stars, and
virtually unfiltered by the dusty FeLoBAL screen. The observed Ly-alpha
emission is best explained if it is produced in the outflowing BAL cloud
system, while the Balmer lines arise primarily from the standard broad emission
line region seen through the dusty (A_V ~ 7 mag.) broad absorption line region.
Two possible geometric models are discussed in the context of these new
results. |
Cosmology with a Decaying Vacuum Energy Parametrization Derived from
Quantum Mechanics: Within the quantum mechanical treatment of the decay problem one finds that
at late times $t$ the survival probability of an unstable state cannot have the
form of an exponentially decreasing function of time $t$ but it has an inverse
power-like form. This is a general property of unstable states following from
basic principles of quantum theory. The consequence of this property is that in
the case of false vacuum states the cosmological constant becomes dependent on
time: $\Lambda - \Lambda_{\text{bare}}\equiv \Lambda(t) -\Lambda_{\text{bare}}
\sim 1/t^{2}$. We construct the cosmological model with decaying vacuum energy
density and matter for solving the cosmological constant problem and the
coincidence problem. We show the equivalence of the proposed decaying false
vacuum cosmology with the $\Lambda(t)$ cosmologies (the $\Lambda(t)$CDM
models). The cosmological implications of the model of decaying vacuum energy
(dark energy) are discussed. We constrain the parameters of the model with
decaying vacuum using astronomical data. For this aim we use the observation of
distant supernovae of type Ia, measurements of $H(z)$, BAO, CMB and others. The
model analyzed is in good agreement with observation data and explain a small
value of the cosmological constant today. | Exploring Early Dark Energy solution to the Hubble tension with Planck
and SPTPol data: A promising idea to resolve the long standing Hubble tension is to postulate
a new subdominant dark-energy-like component in the pre-recombination Universe
which is traditionally termed as the Early Dark Energy (EDE). However, as shown
in Refs. \cite{Hill:2020osr,Ivanov:2020ril} the cosmic microwave background
(CMB) and large-scale structure (LSS) data impose tight constraints on this
proposal. Here, we revisit these strong bounds considering the Planck CMB
temperature anisotropy data at large angular scales and the SPTPol polarization
and lensing measurements. As advocated in Ref. \cite{Chudaykin:2020acu}, this
combined data approach predicts the CMB lensing effect consistent with the
$\Lambda$CDM expectation and allows one to efficiently probe both large and
small angular scales. Combining Planck and SPTPol CMB data with the full-shape
BOSS likelihood and information from photometric LSS surveys in the EDE
analysis we found for the Hubble constant $H_0=69.79\pm0.99\,{\rm
km\,s^{-1}Mpc^{-1}}$ and for the EDE fraction $f_{\rm EDE}<0.094\,(2\sigma)$.
These bounds obtained without including a local distance ladder measurement of
$H_0$ (SH0ES) alleviate the Hubble tension to a $2.5\sigma$ level. Including
further the SH0ES data we obtain $H_0=71.81\pm1.19\,{\rm km\,s^{-1}Mpc^{-1}}$
and $f_{\rm EDE}=0.088\pm0.034$ in full accordance with SH0ES. We also found
that a higher value of $H_0$ does not significantly deteriorate the fit to the
LSS data. Overall, the EDE scenario is (though weakly) favoured over
$\Lambda$CDM even after accounting for unconstrained directions in the
cosmological parameter space. We conclude that the large-scale Planck
temperature and SPTPol polarization measurements along with LSS data do not
rule out the EDE model as a resolution of the Hubble tension. This paper
underlines the importance of the CMB lensing effect for robust constraints on
the EDE scenario. |
The scaling relations and the fundamental plane for radio halos and
relics of galaxy clusters: Diffuse radio emission in galaxy clusters is known to be related to cluster
mass and cluster dynamical state. We collect the observed fluxes of radio
halos, relics, and mini-halos for a sample of galaxy clusters from the
literature, and calculate their radio powers. We then obtain the values of
cluster mass or mass proxies from previous observations, and also obtain the
various dynamical parameters of these galaxy clusters from optical and X-ray
data. The radio powers of relics, halos, and mini-halos are correlated with the
cluster masses or mass proxies, as found by previous authors, with the
correlations concerning giant radio halos being, in general, the strongest
ones. We found that the inclusion of dynamical parameters as the third
dimension can significantly reduce the data scatter for the scaling relations,
especially for radio halos. We therefore conclude that the substructures in
X-ray images of galaxy clusters and the irregular distributions of optical
brightness of member galaxies can be used to quantitatively characterize the
shock waves and turbulence in the intracluster medium responsible for
re-accelerating particles to generate the observed diffuse radio emission. The
power of radio halos and relics is correlated with cluster mass proxies and
dynamical parameters in the form of a fundamental plane. | The far-infrared view of M87 as seen by the Herschel Space Observatory: The origin of the far-infrared emission from the nearby radio galaxy M87
remains a matter of debate. Some studies find evidence of a far-infrared excess
due to thermal dust emission, whereas others propose that the far-infrared
emission can be explained by synchrotron emission without the need for an
additional dust emission component. We observed M87 with PACS and SPIRE as part
of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data
with a synchrotron model based on infrared, submm and radio data to investigate
the origin of the far-infrared emission. We find that both the integrated SED
and the Herschel surface brightness maps are adequately explained by
synchrotron emission. At odds with previous claims, we find no evidence of a
diffuse dust component in M87. |
In Defense of an Accelerating Universe: Model Insensitivity of the
Hubble Diagram: A recently published paper by Nielsen, Guffanti and Sarkar argues that the
evidence for cosmic acceleration is marginal and that a coasting universe - the
Milne Universe - fits the same supernovae data in a Hubble diagram nearly as
well. The Milne Universe has negative spatial curvature. Nevertheless, we
confirm that the Milne model fits the data just as well as LCDM. We show that
this unexpected result points to a weakness in the Hubble diagram rather than
to a flaw in LCDM. It seems the Hubble diagram is insensitive to spatial
curvature. Here we present the data and both models in a scale factor vs.
cosmological time plot.This plot is exquisitely sensitive to spatial curvature
because one of three unique transformations, for each of curvatures 0,+1,-1, is
applied to transform from the Hubble diagram. Although the Milne negative
curvature did not matter much in the Hubble diagram, it matters critically in
the scale factor plot. Given that space is flat as measured by precise CMB
observations, we find that when the SNe data, the LCDM model and the Milne
model are plotted as scale factor vs. cosmological time the two resulting
curves separate at 2 sigma above the noise- ten times their separation above
the noise in the Hubble diagram. The transformed data fit to the LCDM model
confirms, at a 95% confidence level, that the universe is accelerating and the
Milne coasting universe is ruled out. | Results of optical monitoring of 5 SDSS double QSOs with the Nordic
Optical Telescope: We present optical R-band light curves of five SDSS double QSOs (SDSS
J0903+5028, SDSS J1001+5027, SDSS J1206+4332, SDSS J1353+1138, SDSS J1335+0118)
obtained from monitoring at the Nordic Optical Telescope (NOT) between
September 2005 and September 2007. We also present analytical and pixelated
modeling of the observed systems. For SDSS J1206+4332, we measured the time
delay to be 116 days, which, for a Singular Isothermal Ellipsoid model,
corresponds to a Hubble constant of 73 km/s/Mpc. Simultaneous pixeleted
modeling of five other systems for which a time delay has now been previously
measured at the NOT leads to H_0 = 61.5 km/s/Mpc. Finally, by comparing
lightcurves of the two images of each system, suitably shifted by the predicted
or observed time-delays, we found no evidence for microlensing variability over
the course of the monitoring period. |
Dark Energy Survey Year 1 Results: Curved-Sky Weak Lensing Mass Map: We construct the largest curved-sky galaxy weak lensing mass map to date from
the DES first-year (DES Y1) data. The map, about 10 times larger than previous
work, is constructed over a contiguous $\approx1,500 $deg$^2$, covering a
comoving volume of $\approx10 $Gpc$^3$. The effects of masking, sampling, and
noise are tested using simulations. We generate weak lensing maps from two DES
Y1 shear catalogs, Metacalibration and Im3shape, with sources at redshift
$0.2<z<1.3,$ and in each of four bins in this range. In the highest
signal-to-noise map, the ratio between the mean signal-to-noise in the E-mode
and the B-mode map is $\sim$1.5 ($\sim$2) when smoothed with a Gaussian filter
of $\sigma_{G}=30$ (80) arcminutes. The second and third moments of the
convergence $\kappa$ in the maps are in agreement with simulations. We also
find no significant correlation of $\kappa$ with maps of potential systematic
contaminants. Finally, we demonstrate two applications of the mass maps: (1)
cross-correlation with different foreground tracers of mass and (2) exploration
of the largest peaks and voids in the maps. | A Joint GMRT/X-ray study of galaxy groups: We present results from combined low-frequency radio and X-ray studies of
nearby galaxy groups. We consider two main areas: firstly, the evolutionary
process from spiral-dominated, HI-rich groups to elliptical-dominated systems
with hot, X-ray emitting gas halos; secondly, the mechanism of AGN feedback
which appears to balance radiative cooling of the hot halos of evolved groups.
The combination of radio and X-ray observations provides a powerful tool for
these studies, allowing examination of gas in both hot and cool phases, and of
the effects of shock heating and AGN outbursts. Low-frequency radio data are
effective in detecting older and less energetic electron populations and are
therefore vital for the determination of the energetics and history of such
events. We present results from our ongoing study of Stephan's Quintet, a
spiral-rich group in which tidal interactions and shock heating appear to be
transforming HI in the galaxies into a diffuse X-ray emitting halo, and show
examples of AGN feedback from our sample of elliptical-dominated groups, where
multi-band low-frequency radio data have proved particularly useful. |
Limits on Entanglement Effects in the String Landscape from Planck and
BICEP/Keck Data: We consider observational limits on a proposed model of the string landscape
in inflation. In this scenario, effects from the decoherence of entangled
quantum states in long-wavelength modes in the universe result in modifications
to the Friedmann Equation and a corresponding modification to inflationary
dynamics. Previous work by Holman, Mersini-Houghton, and Takahashi suggested
that such effects could provide an explanation for well-known anomalies in the
Cosmic Microwave Background (CMB), such as the lack of power on large scales
and the "cold spot" seen by both the WMAP and Planck satellites. In this paper,
we compute limits on these entanglement effects from the Planck CMB data
combined with the BICEP/Keck polarization measurement, and find no evidence for
observable modulations to the power spectrum from landscape entanglement, and
no sourcing of observable CMB anomalies. The originally proposed model with an
exponential potential is ruled out to high significance. Assuming a
Starobinsky-type $R^2$ inflation model, which is consistent with CMB
constraints, data place a $2\sigma$ lower bound of $b > 6.46 \times 10^7\ {\rm
GeV}$ on the Supersymmetry breaking scale associated with entanglement
corrections. | Correlated orientations of the axes of large quasar groups on Gpc scales: Correlated orientations of quasar optical and radio polarisation, and of
radio jets, have been reported on Gpc scales, possibly arising from intrinsic
alignment of spin axes. Optical quasar polarisation appears to be
preferentially either aligned or orthogonal to the host large-scale structure,
specifically large quasar groups (LQGs). Using a sample of 71 LQGs at redshifts
$1.0 \leq z \leq 1.8$, we investigate whether LQGs themselves exhibit
correlated orientation. We find that LQG position angles (PAs) are unlikely to
be drawn from a uniform distribution ($p$-values $0.008 \lesssim p \lesssim
0.07$). The LQG PA distribution is bimodal, with median modes at
$\bar{\theta}\sim45\pm2^{\circ}, 136\pm2^{\circ}$, remarkably close to the mean
angles of quasar radio polarisation reported in two regions coincident with our
LQG sample. We quantify the degree of alignment in the PA data, and find that
LQGs are aligned and orthogonal across very large scales. The maximum
significance is $\simeq 0.8\%$ ($2.4\sigma$) at typical angular (proper)
separations of $\sim 30^{\circ}$ (1.6 Gpc). If the LQG orientation correlation
is real, it represents large-scale structure alignment over scales larger than
those predicted by cosmological simulations and at least an order of magnitude
larger than any so far observed, with the exception of quasar-polarisation /
radio-jet alignment. We conclude that LQG alignment helps explain
quasar-polarisation / radio-jet alignment, but raises challenging questions
about the origin of the LQG correlation and the assumptions of the concordance
cosmological model. |
Catching the radio flare in CTA 102 I. Light curve analysis: Context: The blazar CTA 102 (z=1.037) underwent a historical radio outburst
in April 2006. This event offered a unique chance to study the physical
properties of the jet. Aims: We used multifrequency radio and mm observations
to analyze the evolution of the spectral parameters during the flare as a test
of the shock-in-jet model under these extreme conditions. Methods: For the
analysis of the flare we took into account that the flaring spectrum is
superimposed on a quiescent spectrum. We reconstructed the latter from archival
data and fitted a synchrotron self-absorbed distribution of emission. The
uncertainties of the derived spectral parameters were calculated using Monte
Carlo simulations. The spectral evolution is modeled by the shock-in-jet model,
and the derived results are discussed in the context of a geometrical model
(varying viewing angle) and shock-shock interaction. Results: The evolution of
the flare in the turnover frequency-turnover flux density plane shows a double
peak structure. The nature of this evolution is dicussed in the frame of
shock-in-jet models. We discard the generation of the double peak structure in
the turnover frequency-turnover flux density plane purely based on geometrical
changes (variation of the Doppler factor). The detailed modeling of the
spectral evolution favors a shock-shock interaction as a possible physical
mechanism behind the deviations from the standard shock-in-jet model. | The star formation history of CALIFA galaxies: Radial structures: We study the radial structure of the stellar mass surface density ($\mu$) and
stellar population age as a function of the total stellar mass and morphology
for a sample of 107 galaxies from the CALIFA survey. We use the fossil record
to recover the star formation history (SFH) in spheroidal and disk dominated
galaxies with masses from 10$^9$ to 10$^{12}$ M$_\odot$. We derive the half
mass radius, and we find that galaxies are on average 15% more compact in mass
than in light. HMR/HLR decreases with increasing mass for disk galaxies, but is
almost constant in spheroidal galaxies. We find that the galaxy-averaged
stellar population age, stellar extinction, and $\mu$ are well represented by
their values at 1 HLR. Negative radial gradients of the stellar population ages
support an inside-out formation. The larger inner age gradients occur in the
most massive disk galaxies that have the most prominent bulges; shallower age
gradients are obtained in spheroids of similar mass. Disk and spheroidal
galaxies show negative $\mu$ gradients that steepen with stellar mass. In
spheroidal galaxies $\mu$ saturates at a critical value that is independent of
the galaxy mass. Thus, all the massive spheroidal galaxies have similar local
$\mu$ at the same radius (in HLR units). The SFH of the regions beyond 1 HLR
are well correlated with their local $\mu$, and follow the same relation as the
galaxy-averaged age and $\mu$; suggesting that local stellar mass surface
density preserves the SFH of disks. The SFH of bulges are, however, more
fundamentally related to the total stellar mass, since the radial structure of
the stellar age changes with galaxy mass even though all the spheroid dominated
galaxies have similar radial structure in $\mu$. Thus, galaxy mass is a more
fundamental property in spheroidal systems while the local stellar mass surface
density is more important in disks. |
Strongly scale-dependent CMB dipolar asymmetry from super-curvature
fluctuations: We reconsider the observed CMB dipolar asymmetry in the context of open
inflation, where a supercurvature mode might survive the bubble nucleation. If
such a supercurvature mode modulates the amplitude of the curvature power
spectrum, it would easily produce an asymmetry in the power spectrum. We show
that current observational data can be accommodated in a three-field model,
with simple quadratic potentials and a non-trivial field-space metric. Despite
the presence of three fields, we believe this model is so far the simplest that
can match current observations. We are able to match the observed strong scale
dependence of the dipolar asymmetry, without a fine tuning of initial
conditions, breaking slow roll or adding a feature to the evolution of any
field. | Universal subhalo accretion in cold and warm dark matter cosmologies: The influence of the large scale structure on host halos may be studied by
examining the angular infall pattern of subhalos. In particular, since warm and
cold dark matter cosmologies predict different abundances and internal
properties for halos at the low mass end of the mass function, it is
interesting to examine if there are differences in how these low mass halos are
accreted. The accretion events are defined as the moment a halo becomes a
substructure, namely when it crosses its host's virial radius. We quantify the
cosmic web at each point by the shear tensor and examine where, with respect to
its eigenvectors, such accretion events occur in cold ($\Lambda$CDM) and warm
(1keV sterile neutrino WDM) dark matter cosmological models. We find that the
CDM and WDM subhalos are preferentially accreted along the principal axis of
the shear tensor corresponding to the direction of weakest collapse. The
beaming strength is modulated by the host and subhalo masses and by the
redshift at which the accretion event occurs. Although strongest for the most
massive hosts and subhalos at high redshift, the preferential infall is found
to be always aligned with the axis of weakest collapse, thus we say that it has
universal nature. We compare the strength of beaming in the WDM cosmology with
the one found in the $\Lambda$CDM scenario. While the main findings remain the
same, the accretion in the WDM model for the most massive host halos appears
more beamed than in $\Lambda$CDM cosmology across all the redshifts. |
A new perspective on cosmology through Supernovae Ia and Gamma Ray
Bursts: The actual knowledge of the structure and future evolution of our universe is
based on the use of cosmological models, which can be tested through the
so-called 'probes', namely astrophysical phenomena, objects or structures with
peculiar properties that can help to discriminate among different cosmological
models. Among all the existing probes, of particular importance are the
Supernovae Ia (SNe Ia) and the Gamma Ray Bursts (GRBs): the former are
considered among the best standard candles so far discovered but suffer from
the fact that can be observed until redshift $z=2.26$, while the latter are
promising standardizable candles which have been observed up to $z=9.4$,
surpassing even the farthest quasar known to date, which is at $z=7.64$. The
standard candles can be used to test the cosmological models and to give the
expected values of cosmological parameters, in particular the Hubble constant
value. The Hubble constant is affected by the so-called \say{Hubble constant
tension}, a discrepancy in more than 4 $\sigma$ between its value measured with
local probes and its value measured through the cosmological probes. The
increase in the number of observed SNe Ia, as well as the future
standardization of GRBs through their correlations, will surely be of help in
alleviating the Hubble constant tension and in explaining the structure of the
universe at higher redshifts. A promising class of GRBs for future
standardization is represented by the GRBs associated with Supernovae Ib/c,
since these present features similar to the SNe Ia class and obey a tight
correlation between their luminosity at the end of the plateau emission in
X-rays and the time at the end of the plateau in the rest-frame. | Active Galaxies in the Sloan Digital Sky Survey III: from quasars to
radio galaxies?: In this third of a series of papers concerning active galaxies in the FIRST
and Sloan Digital Sky Surveys, we analyze the spectroscopic and radio
properties of a sample of narrow-line Active Galactic Nuclei (AGN), broad-line
Seyfert I galaxies, and Quasars in the local universe in order to investigate
the dependence of their activity on the mass, spin and accretion rates of the
supermassive black holes (SMBH) residing at the centers of their host galaxies.
We show that galaxies hosting more massive SMBH are more likely to power
stronger and larger radio jets, and we show a strong anti-correlation between
the strength of the lines of radio emitting galaxies and their radio power.
Furthermore we show that the compactness of a jet is correlated with the epoch
of the last episode of star-formation, suggesting a link between the presence
of cold gas in a galaxy, the size of its SMBH and the radio and spectroscopic
features of its AGN. We use our large statistical sample to test the
expectations of unified models of AGN based on orientation. While confirming
that Seyfert II galaxies and radio galaxies are significantly more extincted
then Seyfert Is and nearby Quasars, we find several major inconsistencies with
such a paradigm. In particular we show a strong difference in the [OIII],[OII]
and [NII] luminosities for different spectroscopic classes, a result which
argues in favor of an evolution of the broad and narrow line regions of active
nuclei over time.
We suggests that evolution, rather than orientation, may be the key element
in shaping the properties of active nuclei, as also suggested by the results of
high-redshift X-ray and radio surveys and we speculate on a model that may
predict this kind of evolution. |
Impacts of Hawking Radiation from Primordial Black Holes in Critical
Collapse Model on the Light Element Abundances: We study the photodisintegration process triggered by the nonthermal
electromagnetic Hawking radiation from primordial black holes (PBHs) in
critical collapse model. We consider the simplest case that all PBHs formed at
a single epoch stemming from an inflationary spectrum with a narrow peak, and
an extended mass distribution is obtained due to critical phenomena of
gravitational collapse. The presence of a low-mass tail of critical collapse
mass function could lead to an enhancement of energetic photon emissions from
Hawking radiation of PBHs. Nuclear photodisintegration rates are calculated
with a nonthermal photon spectrum derived by solving the Boltzmann equation
iteratively. The exact spectrum is much different than that based on an
often-used analytical bended power-law spectrum and it is found to
significantly depend on the adopted PBH mass functions. With the newest
observational limit on the $^3$He abundance in Galactic H II regions, the
updated $^3$He constraints on PBH mass spectrum in the horizon mass range
$10^{12} - 10^{13}$ g are derived. Our results for the first time show that
$^3$He constraints on the critical mass function are about one order of
magnitude severer than the monochromatic one although the fraction of PBHs in
the low-mass tail region is relatively small. The $^6$Li elemental abundance is
also enhanced significantly for the critical mass function. More precise
measurement of $^6$Li abundance is highly desirable to provide a promising
constraint on PBHs in the future. For monochromatic mass function, we provide
the analytical bounds for photodisintegration and hadrodissociation from PBH
radiation, and we report discrepancies between our updated $^3$He constraints
and the previous results. | Molecular lines as tracers of Compton-thick AGN ?: Recently, Papadopoulos et al., 2010 using sub-mm CO molecular line
observations of nearby ultra-luminous IRAS galaxies, (U)LIRGs, have found that
exceptionally large gas column densities (N_H > 10^25 cm-2) can be present
across some of the very dense gaseous disks that are typically found in these
objects. They also proposed a diagnostic for finding such sources using CO and
HCN molecular lines. Given that such high column densities are expected to
absorb any X-ray luminous AGN, yielding Compton-thick sources, we set out
toexplore whether this can be discerned using X-ray observations. More
specifically we examine X-ray spectral observations of 14 sources in their
sample, using public Chandra observations (0.5-10 keV) for eleven sources as
well as BeppoSAX results (2-100 keV) from the literature for another three
sources. Our goal is to find candidate Compton-thick AGN and to check whether
the molecular line selection criterion is successful in selecting such systems.
X-ray spectroscopy reveals four candidate Compton-thick AGN of which half fall
within the high obscuration region in the molecular line ratio diagnostics. Of
the remaining five sources falling into the `high dust obscuration' box, one
(Mrk273) is highly obscured (N_H ~4x10^23 cm-2) while in the other four the
X-ray emission is most probably associated with star-forming processes rather
than an AGN on the basis of their X-ray and mid-infrared properties. Overall,
we argue that although this method as expected cannot recover all Compton-thick
AGN, there are no examples of X-ray luminous AGN inside that region that have
low obscuration, suggesting that this method is efficient in finding heavily
obscured AGN in dust-enshrouded star-forming galaxies. The above results bear
important implications for future joint ALMA and X-ray observations for the
detection of Compton-thick AGN. |
Reconstruction of late-time cosmology using Principal Component Analysis: We reconstruct late-time cosmology using the technique of Principal Component
Analysis (PCA). In particular, we focus on the reconstruction of the dark
energy equation of state from two different observational data-sets, Supernovae
type Ia data, and Hubble parameter data. The analysis is carried out in two
different approaches. The first one is a derived approach, where we reconstruct
the observable quantity using PCA and subsequently construct the equation of
state parameter. The other approach is the direct reconstruction of the
equation of state from the data. A combination of PCA algorithm and calculation
of correlation coefficients are used as prime tools of reconstruction. We carry
out the analysis with simulated data as well as with real data. The derived
approach is found to be statistically preferable over the direct approach. The
reconstructed equation of state indicates a slowly varying equation of state of
dark energy. | Gravitational effects of the faraway matter on the rotation curves of
spiral galaxies: It was recently shown that in cosmology the gravitational action of faraway
matter has quite relevant effects, if retardation of the forces and
discreteness of matter (with its spatial correlation) are taken into account.
Indeed, far matter was found to exert, on a test particle, a force per unit
mass of the order of 0.2 cH0 . It is shown here that such a force can account
for the observed rotational velocity curves in spiral galaxies, if the force is
assumed to be decorrelated beyond a sufficiently large distance, of the order
of 1 kpc. In particular we fit the rotation curves of the galaxies NGC 3198,
NGC 2403, UGC 2885 and NGC 4725 without any need of introducing dark matter at
all. Two cases of galaxies presenting faster than keplerian decay are also
considered. |
Method of analysis of the spatial galaxy distribution at gigaparsec
scales. I. Initial principles: Initial principles of a method of analysis of the luminous matter spatial
distribution with sizes about thousands Mpc are presented. The method is based
on an analysis of the photometric redshift distribution N(z) in the deep fields
with large redshift bins \Deltaz=0.1{\div}0.3. Number density fluctuations in
the bins are conditioned by the Poisson's noise, the correlated structures and
the systematic errors of the photo-z determination. The method includes
covering of a sufficiently large region on the sky by a net of the deep
multiband surveys with the sell size about 10^{\circ}x10^{\circ} where
individual deep fields have angular size about 10'x10' and may be observed at
telescopes having diameters 3-10 meters. The distributions of photo-z within
each deep field will give information about the radial extension of the super
large structures while a comparison of the individual radial distributions of
the net of the deep fields will give information on the tangential extension of
the super large structures. A necessary element of the method is an analysis of
possible distortion effects related to the methodic of the photo-z
determination. | Consistency of nonlinear interacting ghost dark energy with recent
observations: In this paper we investigate ghost dark energy model in the presence of
non-linear interaction between dark energy and dark matter. We also extend the
analysis to the so called generalized ghost dark energy (GGDE) which
$\rho_D=\alpha H+\beta H^2$. The model contains three free parameters as
$\Omega_D, \zeta(=\frac{8\pi G \beta}{3})$ and $b^2$ (the coupling coefficient
of interactions). We propose three kinds of non-linear interaction terms and
discuss the behavior of equation of state, deceleration and dark energy density
parameters of the model. We also find the squared sound speed and search for
signs of stability of the model. To compare the interacting GGDE model with
observational data sets, we use more recent observational outcomes, namely SNIa
from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most
relevant CMB parameters including, the position of acoustic peaks, shift
parameters and redshift to recombination. For GGDE with the first non-linear
interaction, the joint analysis indicates that $\Omega_D=0.7192\pm0.0062$,
$b^2=0.146^{+0.030}_{-0.026}$ and $\zeta=0.104\pm0.047$ at 1 optimal variance
error. For the second interaction, the best fit values at $1\sigma$ confidence
are $\Omega_D=0.72091\pm0.0065$, $b^2=0.0395\pm0.0080$ and $\zeta\le0.0173$.
According to combination of all observational data sets considered in this
paper the best fit values for third non-linearly interacting model are
$\Omega_D=0.7287\pm0.0062$, $b^2=0.0109\pm0.0023$ and $\zeta\le0.00764$ at
$1\sigma$ confidence interval. Finally we found that the presence of
interaction is compatible in mentioned models via current observational data
sets. |
Baryon Acoustic Oscillation detections from the clustering of massive
halos and different density region tracers in TianNu simulation: The Baryon Acoustic Oscillations (BAO) refer to the ripples of material
density in the Universe. As the most direct density tracers in the universe,
galaxies have been commonly used in studies of BAO peak detection. The spatial
number density of galaxies, to a certain extent, reflects the distribution of
the material density of our Universe. Using galaxies as matter tracers, we can
construct more overlapping empty spheres (DT voids) than the matter tracers,
via Delaunay Triangulation technique. We show that their radii excellently
reflect the galaxy number density round them, and they can serve as reliable
different density region tracers. Using the data from an unprecedented
large-scale $N$-body simulation "TianNu", we conduct some fundamental
statistical studies and clustering analysis of the DT voids. We discuss in
detail the representative features of two-point correlation functions of
different DT void populations. We show that the peak, the position of which
corresponds to the average radius of data samples, is the most representative
feature of the two-point correlation function of the DT voids. In addition, we
also construct another voids, the disjoint voids, and investigate their some
statistical properties and clustering properties. And we find that the occupied
space of all disjoint voids accounts for about $45\%$ of the volume of the
simulation box, regardless of the number density of mock galaxies. We also
investigate the BAO detections based on different tracers, i.e. mock galaxies,
low-density region tracers, and high-density region tracers respectively. Our
results show that BAO intensities detected by low/high-density region tracers
are enhanced significantly compared to the BAO detection by mock galaxies, for
the mock galaxy catalogue with the number density of $7.52\times10^{-5}$ $h^3$
Mpc$^{-3}$. | Comment on "The Real Problem with MOND" by Scott Dodelson,
arXiv:1112.1320: We comment on arXiv:1112.1320 and point out that baryonic oscillations of the
matter power spectrum, while predicted by theories that do not incorporate
collisionless cold dark matter, are strongly suppressed by the statistical
window function that is used to process finite-sized galaxy samples. We assert
that with present-day data sets, the slope of the matter power spectrum is a
much stronger indicator of a theory's validity. We also argue that MOND should
not be used as a strawman theory as it is not in general representative of
modified gravity theories; some theories, notably our scalar-vector-tensor
MOdified Gravity (MOG), offer much more successful predictions of cosmological
observations. |
Missing Power vs low-l Alignments in the Cosmic Microwave Background: No
Correlation in the Standard Cosmological Model: On large angular scales (greater than about 60 degrees), the two-point
angular correlation function of the temperature of the cosmic microwave
background (CMB), as measured (outside of the plane of the Galaxy) by the
Wilkinson Microwave Anisotropy Probe, shows significantly lower large-angle
correlations than expected from the standard inflationary cosmological model.
Furthermore, when derived from the full CMB sky, the two lowest cosmologically
interesting multipoles, the quadrupole (l=2) and the octopole (l=3), are
unexpectedly aligned with each other. Using randomly generated full-sky and
cut-sky maps, we investigate whether these anomalies are correlated at a
statistically significant level. We conclusively demonstrate that, assuming
Gaussian random and statistically isotropic CMB anisotropies, there is no
statistically significant correlation between the missing power on large
angular scales in the CMB and the alignment of the l=2 and l=3 multipoles. The
chance to measure the sky with both such a lack of large-angle correlation and
such an alignment of the low multipoles is thus quantified to be below 10^{-6}. | Efficient cosmological parameter sampling using sparse grids: We present a novel method to significantly speed up cosmological parameter
sampling. The method relies on constructing an interpolation of the
CMB-log-likelihood based on sparse grids, which is used as a shortcut for the
likelihood-evaluation. We obtain excellent results over a large region in
parameter space, comprising about 25 log-likelihoods around the peak, and we
reproduce the one-dimensional projections of the likelihood almost perfectly.
In speed and accuracy, our technique is competitive to existing approaches to
accelerate parameter estimation based on polynomial interpolation or neural
networks, while having some advantages over them. In our method, there is no
danger of creating unphysical wiggles as it can be the case for polynomial fits
of a high degree. Furthermore, we do not require a long training time as for
neural networks, but the construction of the interpolation is determined by the
time it takes to evaluate the likelihood at the sampling points, which can be
parallelised to an arbitrary degree. Our approach is completely general, and it
can adaptively exploit the properties of the underlying function. We can thus
apply it to any problem where an accurate interpolation of a function is
needed. |
The Energetics of Molecular Gas in NGC 891 from H2 and FIR Spectroscopy: We have studied the molecular hydrogen energetics of the edge-on spiral
galaxy NGC\,891, using a 34-position map in the lowest three pure rotational
H$_2$ lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1),
and S(2) lines are bright with an extinction corrected total luminosity of
$\sim2.8 \times 10^{7}$ L$_{\odot}$, or 0.09\% of the total-infrared luminosity
of NGC\,891. The H$_2$ line ratios are nearly constant along the plane of the
galaxy -- we do not observe the previously reported strong drop-off in the
S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find
no evidence for the very massive cold CO-free molecular clouds invoked to
explain the past observations. The H$_2$ level excitation temperatures increase
monotonically indicating more than one component to the emitting gas. More than
99\% of the mass is in the lowest excitation (T$_{ex}$ $\sim$125 K) ``warm''
component. In the inner galaxy, the warm H$_2$ emitting gas is $\sim$15\% of
the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction
is twice as high. This large mass of warm gas is heated by a combination of the
far-UV photons from stars in photo-dissociation regions (PDRs) and the
dissipation of turbulent kinetic energy. Including the observed far-infrared
[OI] and [CII] fine-structure line emission and far-infrared continuum emission
in a self-consistent manner to constrain the PDR models, we find essentially
all of the S(0) and most (70\%) of the S(1) line arises from low excitation
PDRs, while most (80\%) of the S(2) and the remainder of the S(1) line emission
arises from low velocity microturbulent dissipation. | Growing a `Cosmic Beast': Observations and Simulations of MACS
J0717.5+3745: We present a gravitational lensing and X-ray analysis of a massive galaxy
cluster and its surroundings. The core of MACS\,J0717.5+3745 ($M(R<1\,{\rm
Mpc})\sim$\,$2$$\times$$10^{15}\,\msun$, $z$=$0.54$) is already known to
contain four merging components. We show that this is surrounded by at least
seven additional substructures with masses ranging from
$3.8-6.5\times10^{13}\,\msun$, at projected radii $1.6$ to $4.9$\,Mpc. We
compare MACS\,J0717 to mock lensing and X-ray observations of similarly rich
clusters in cosmological simulations. The low gas fraction of substructures
predicted by simulations turns out to match our observed values of $1$--$4\%$.
Comparing our data to three similar simulated halos, we infer a typical growth
rate and substructure infall velocity. That suggests MACS\,J0717 could evolve
into a system similar to, but more massive than, Abell\,2744 by $z=0.31$, and
into a $\sim$\,$10^{16}\,\msun$ supercluster by $z=0$. The radial distribution
of infalling substructure suggests that merger events are strongly episodic;
however we find that the smooth accretion of surrounding material remains the
main source of mass growth even for such massive clusters. |
From Dark Matter to Galaxies with Convolutional Neural Networks: Cosmological simulations play an important role in the interpretation of
astronomical data, in particular in comparing observed data to our theoretical
expectations. However, to compare data with these simulations, the simulations
in principle need to include gravity, magneto-hydrodyanmics, radiative
transfer, etc. These ideal large-volume simulations
(gravo-magneto-hydrodynamical) are incredibly computationally expensive which
can cost tens of millions of CPU hours to run. In this paper, we propose a deep
learning approach to map from the dark-matter-only simulation (computationally
cheaper) to the galaxy distribution (from the much costlier cosmological
simulation). The main challenge of this task is the high sparsity in the target
galaxy distribution: space is mainly empty. We propose a cascade architecture
composed of a classification filter followed by a regression procedure. We show
that our result outperforms a state-of-the-art model used in the astronomical
community, and provides a good trade-off between computational cost and
prediction accuracy. | Dark Energy Survey Year 3 Results: Constraints on cosmological
parameters and galaxy bias models from galaxy clustering and galaxy-galaxy
lensing using the redMaGiC sample: We constrain cosmological and galaxy-bias parameters using the combination of
galaxy clustering and galaxy-galaxy lensing measurements from the Dark Energy
Survey Year-3 data. We describe our modeling framework, and choice of scales
analyzed, validating their robustness to theoretical uncertainties in
small-scale clustering by analyzing simulated data. Using a linear galaxy bias
model and redMaGiC galaxy sample, we obtain constraints on the matter density
to be $\Omega_{\rm m} = 0.325^{+0.033}_{-0.034}$. We also implement a
non-linear galaxy bias model to probe smaller scales that includes
parameterization based on hybrid perturbation theory and find that it leads to
a 17% gain in cosmological constraining power. We perform robustness tests of
our methodology pipeline and demonstrate the stability of the constraints to
changes in the theoretical model. Using the redMaGiC galaxy sample as
foreground lens galaxies, we find the galaxy clustering and galaxy-galaxy
lensing measurements to exhibit significant signals akin to de-correlation
between galaxies and mass on large scales, which is not expected in any current
models. This likely systematic measurement error biases our constraints on
galaxy bias and the $S_8$ parameter. We find that a scale-, redshift- and
sky-area-independent phenomenological de-correlation parameter can effectively
capture the impact of this systematic error. We trace the source of this
de-correlation to a color-dependent photometric issue and minimize its impact
on our result by changing the selection criteria of redMaGiC galaxies. Using
this new sample, our constraints on the $S_8$ parameter are consistent with
previous studies, and we find a small shift in the $\Omega_{\rm m}$ constraints
compared to the fiducial redMaGiC sample. We constrain the mean host halo mass
of the redMaGiC galaxies in this new sample to be approximately $1.6 \times
10^{13} M_{\odot}/h$. |
Modeling Emission from the First Explosions: Pitfalls and Problems: Observations of the explosions of Population III (Pop III) stars have the
potential to teach us much about the formation and evolution of these
zero-metallicity objects. To realize this potential, we must tie observed
emission to an explosion model, which requires accurate light curve and spectra
calculations. Here, we discuss many of the pitfalls and problems involved in
such models, presenting some preliminary results from radiation-hydrodynamics
simulations. | Hybrid Cosmological Simulations with Stream Velocities: In the early universe, substantial relative "stream" velocities between the
gas and dark matter arise due to radiation pressure and persist after
recombination. To asses the impact of these velocities on high-redshift
structure formation, we carry out a suite of high-resolution Adaptive Mesh
Refinement (AMR) cosmological simulations, which use Smoothed Particle
Hydrodynamic datasets as initial conditions, converted using a new tool
developed for this work. These simulations resolve structures with masses as
small as a few 100 M$_\odot$, and we focus on the $10^6$ M$_\odot$ "mini-halos"
in which the first stars formed. At $z \approx 17,$ the presence of stream
velocities has only a minor effect on the number density of halos below $10^6$
M$_\odot$, but it greatly suppresses gas accretion onto all halos and the dark
matter structures around them. Stream velocities lead to significantly lower
halo gas fractions, especially for $\approx 10^5$ M$_\odot$ objects, an effect
that is likely to depend on the orientation of a halo's accretion lanes. This
reduction in gas density leads to colder, more compact radial profiles, and it
substantially delays the redshift of collapse of the largest halos, leading to
delayed star formation and possibly delayed reionization. These many
differences suggest that future simulations of early cosmological structure
formation should include stream velocities to properly predict gas evolution,
star-formation, and the epoch of reionization. |
Forecasts on neutrino mass constraints from the redshift-space two-point
correlation function: We provide constraints on the accuracy with which the neutrino mass fraction,
$f_{\nu}$, can be estimated when exploiting measurements of redshift-space
distortions, describing in particular how the error on neutrino mass depends on
three fundamental parameters of a characteristic galaxy redshift survey:
density, halo bias and volume. In doing this, we make use of a series of dark
matter halo catalogues extracted from the BASICC simulation. The mock data are
analysed via a Markov Chain Monte Carlo likelihood analysis. We find a fitting
function that well describes the dependence of the error on bias, density and
volume, showing a decrease in the error as the bias and volume increase, and a
decrease with density down to an almost constant value for high density values.
This fitting formula allows us to produce forecasts on the precision achievable
with future surveys on measurements of the neutrino mass fraction. For example,
a Euclid-like spectroscopic survey should be able to measure the neutrino mass
fraction with an accuracy of $\delta f_{\nu} \approx 6.7\times10^{-4}$, using
redshift-space clustering once all the other cosmological parameters are kept
fixed to the $\Lambda$CDM case. | Revisiting a model-independent dark energy reconstruction method: Model independent reconstructions of dark energy have received some
attention. The approach that addresses the reconstruction of the dimensionless
coordinate distance and its two first derivatives using a polynomial fit in
different redshift windows is well developed
\cite{DalyDjorgovski1,DalyDjorgovski2,DalyDjorgovski3}. In this work we offer
new insights into the problem by focusing on two types of observational probes:
SNeIa and GRBs. Our results allow to highlight some of the intrinsic weaknesses
of the method. One of the directions we follow is to consider updated
observational samples. Our results indicate than conclusions on the main dark
energy features as drawn from this method are intimately related to the
features of the samples themselves (which are not quite ideal). This is
particularly true of GRBs, which manifest themselves as poor performers in this
context. In contrast to original works, we conclude they cannot be used for
cosmological purposes, and the state of the art does not allow to regard them
on the same quality basis as SNeIa. The next direction we contribute to is the
question of how the adjusting of some parameters (window width, overlap,
selection criteria) affect the results. We find again there is a considerable
sensitivity to these features. Then, we try to establish what is the current
redshift range for which one can make solid predictions on dark energy
evolution. Finally, we strengthen the former view that this model is modest in
the sense it provides only a picture of the global trend. But, on the other
hand, we believe it offers an interesting complement to other approaches given
that it works on minimal assumptions. |
Template fitting of WMAP 7-year data: anomalous dust or flattening
synchrotron emission?: Anomalous microwave emission at 20-40 GHz has been detected across our
Galactic sky. It is highly correlated with thermal dust emission and hence it
is thought to be due to spinning dust grains. Alternatively, this emission
could be due to synchrotron radiation with a flattening (hard) spectral index.
We cross-correlate synchrotron, free-free and thermal dust templates with the
WMAP 7-year maps using synchrotron templates at both 408 MHz and 2.3 GHz to
assess the amount of flat synchrotron emission that is present, and the impact
that this has on the correlations with the other components. We find that there
is only a small amount of flattening visible in the synchrotron spectral
indices by 2.3 GHz, of around \Delta \beta ~ 0.05, and that the significant
level of dust-correlated emission in the lowest WMAP bands is largely
unaffected by the choice of synchrotron template, particularly at high
latitudes (it decreases by only ~7 per cent when using 2.3 GHz rather than 408
MHz). This agrees with expectation if the bulk of the anomalous emission is
generated by spinning dust grains. | Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies: We report the detection of spatially resolved CO(1-0) emission in the z~3.4
submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the
Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two
previously reported millimeter sources H6 and H7, separated by ~30kpc in
projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86)
and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) =
(23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x
higher than what is expected from simple excitation modeling of higher-J CO
lines, suggesting the presence of copious amounts of low-excitation gas. This
is supported by the finding that the CO(1-0) line in SMM J13120+4242, the
system with lowest CO excitation, appears to have a broader profile and more
extended spatial structure than seen in higher-J CO lines (which is less
prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation
modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and
M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0)
properties are consistent with the picture that SMM J09431+4700 represents an
early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a
system in an advanced stage. This study thus highlights the importance of
spatially and dynamically resolved CO(1-0) observations of SMGs to further
understand the gas physics that drive star formation in these distant galaxies,
which becomes possible only now that the EVLA rises to its full capabilities. |
Nearest neighbor vector analysis of sdss dr5 galaxy distribution: We present the Nearest Neighbor Distance (NND) analysis of SDSS DR5 galaxies.
We give NND results for observed, mock and random sample, and discuss the
differences. We find that the observed sample gives us a significantly stronger
aggregation characteristic than the random samples. Moreover, we investigate
the direction of NND and find that the direction has close relation with the
size of the NND for the observed sample. | Hamilton-Jacobi formalism for Generalized Chaplygin Gas models: In this work we discuss the application of the Hamilton-Jacobi formalism on
the scalar field implementation of Generalized Chaplygin Gas models. This
corresponds to a Generalised Born-Infeld action for the scalar field, which in
an initial fast-rolling phase mimics a matter-like behavior and in the final
slow-rolling phase mimics a cosmological constant. In order to enrich the
phenomenology of the model, we add an extra functional freedom, specified
through a scalar potential for the field. Interestingly, we find that, due to
the lifting induced by the non-standard kinetic term, an asymptotic de
Sitter-like configuration can be obtained even for negative potentials. We show
that at the background level, this model can easily mimic the {\Lambda}CDM
model both with and without independent baryonic and radiation components. |
Coarse-grained cosmological perturbation theory: stirring up the dust
model: We study the effect of coarse-graining the dynamics of a pressureless
selfgravitating fluid (coarse-grained dust) in the context of cosmological
perturbation theory, both in the Eulerian und Lagrangian framework. We obtain
recursion relations for the Eulerian perturbation kernels of the coarse-grained
dust model by relating them to those of the standard pressureless fluid model.
The effect of the coarse-graining is illustrated by means of power and cross
spectra for density and velocity that are computed up to 1-loop order. In
particular, the large scale vorticity power spectrum that arises naturally from
a mass-weighted velocity is derived from first principles. We find
qualitatively good agreement of the magnitude, shape and spectral index of the
vorticity power spectrum with recent measurements from N-body simulations and
results from the effective field theory of large scale structure. To lay the
ground for applications in the context of Lagrangian perturbation theory we
finally describe how the kernels obtained in Eulerian space can be mapped to
Lagrangian ones. | Eliminating Error in the Chemical Abundance Scale for Extragalactic HII
Regions: In an attempt to remove the systematic errors which have plagued the
calibration of the HII region abundance sequence, we have theoretically modeled
the extragalactic HII region sequence. We then used the theoretical spectra so
generated in a double blind experiment to recover the chemical abundances using
both the classical electron temperature + ionization correction factor
technique, and the technique which depends on the use of strong emission lines
(SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a
number of systematic trends, and we provide correction formulae which should
remove systematic errors in the electron temperature + ionization correction
factor technique. We also provide a critical evaluation of the various
semi-empirical SEL techniques. Finally, we offer a scheme which should help to
eliminate systematic errors in the SEL-derived chemical abundance scale for
extragalactic HII regions. |
An Atlas of z=5.7 and z=6.5 Ly alpha Emitters: We present an atlas of 88 z~5.7 and 30 z~6.5 Ly alpha emitters obtained from
a wide-field narrowband survey. We combined deep narrowband imaging in 120A
bandpass filters centered at 8150A and 9140A with deep BVRIz broadband imaging
to select high-redshift galaxy candidates over an area of 4180 square arcmin.
The goal was to obtain a uniform selection of comparable depth over the 7
targeted fields in the two filters. For the GOODS-N region of the HDF-N field,
we also selected candidates using a 120A filter centered at 9210A. We made
spectroscopic observations with Keck DEIMOS of nearly all the candidates to
obtain the final sample of Ly alpha emitters. At the 3.3A resolution of the
DEIMOS observations the asymmetric profile for Ly alpha emission with its steep
blue fall-off can be clearly seen in the spectra of nearly all the galaxies. We
show that the spectral profiles are surprisingly similar for many of the
galaxies and that the composite spectral profiles are nearly identical at z=5.7
and z=6.5. We analyze the distributions of line widths and Ly alpha equivalent
widths and find that the lines are marginally narrower at the higher redshift,
with median values of 0.77A at z=6.5 and 0.92A at z=5.7. The line widths have a
dependence on the Ly alpha luminosity of the form L(L alpha)^(0.3). We compare
the surface densities and the luminosity functions at the two redshifts and
find that there is a multiplicative factor of 2 decrease in the number density
of bright Ly alpha emitters from z=5.7 to z=6.5, while the characteristic
luminosity is unchanged. | Modulated reheating by curvaton: There might be a light scalar field during inflation which is not responsible
for the accelerating inflationary expansion. Then, its quantum fluctuation is
stretched during inflation. This scalar field could be a curvaton, if it decays
at a late time. In addition, if the inflaton decay rate depends on the light
scalar field expectation value by interactions between them, density
perturbations could be generated by the quantum fluctuation of the light field
when the inflaton decays. This is modulated reheating mechanism. We study
curvature perturbation in models where a light scalar field does not only play
a role of curvaton but also induce modulated reheating at the inflaton decay.
We calculate the non-linearity parameters as well as the scalar spectral index
and the tensor-to-scalar ratio. We find that there is a parameter region where
non-linearity parameters are also significantly enhanced by the cancellation
between the modulated effect and the curvaton contribution. For the simple
quadratic potential model of both inflaton and curvaton, both tensor-to-scalar
ratio and nonlinearity parameters could be simultaneously large. |
A hidden radio halo in A1682?: High sensitivity observations of radio halos in galaxy clusters at
frequencies lower than 330 MHz are still relatively rare, and very little is
known compared to the classical 1.4 GHz images. The few radio halos imaged down
to 150-240 MHz show a considerable spread in size, morphology and spectral
properties. All clusters belonging to the GMRT Radio Halo Survey with detected
or candidate cluster-scale diffuse emission have been imaged at 325 MHz with
the GMRT. Few of them were also observed with the GMRT at 240 MHz and 150 MHz.
For A1682, imaging is particularly challenging due to the presence of strong
and extended radio galaxies at the center. Our data analysis suggests that the
radio galaxies are superposed to very low surface brightness radio emission
extended on the cluster scale, which we present here. | CosmicFish Implementation Notes V1.0: CosmicFish is a publicly available library to perform Fisher matrix forecast
for several cosmological observations. With the present implementation notes we
provide a guide to the physical and technical details of the library. We
reproduce here the details and all the relevant equations, as they appear in
the code. We submit these notes to the arXiv to grant full and permanent access
to this material which provides a useful guidance to forecasting and the use of
CosmicFish code. We will update this set of notes when relevant modifications
to the CosmicFish code will be released. The present version is based on
CosmicFish Jun16. |
Exploring uncertainties in dark energy constraints using current
observational data with Planck 2015 distance priors: We present the distance priors that we have derived from the 2015 Planck
data, and use these in combination with the latest observational data from Type
Ia Supernovae (SNe Ia) and galaxy clustering, to explore the systematic
uncertainties in dark energy constraints. We use the Joint Lightcurve Analysis
(JLA) set of 740 SNe Ia, galaxy clustering measurements of H(z)s and D_A(z)/s
(where s is the sound horizon at the drag epoch) from the Sloan Digital Sky
Survey (SDSS) at z=0.35 and z=0.57 (BOSS DR12). We find that the combined dark
energy constraints are insensitive to the assumptions made in the galaxy
clustering measurements (whether they are for BAO only or marginalized over
RSD), which indicates that as the analysis of galaxy clustering data becomes
more accurate and robust, the systematic uncertainties are reduced. On the
other hand, we find that flux-averaging SNe Ia at z>= 0.5 significantly
tightens the dark energy constraints, and excludes a flat universe with a
cosmological constant at 68% confidence level, assuming a dark energy equation
of state linear in the cosmic scale factor. Flux-averaging has the most
significant effect when we allow dark energy density function X(z) to be a free
functions given by the cubic spline of its value at z=0, 1/3, 2/3, 1; the
measured X(z) deviates from a cosmological constant at more than 95% confidence
level for 0.4 < z < 0.7. Since flux-averaging reduces the bias in the SN
distance measurements, this may be an indication that we have arrived in the
era when the SN distance measurements are limited by systematic uncertainties. | Replacing dark energy by silent virialisation: Standard cosmological $N$-body simulations have background scale factor
evolution that is decoupled from non-linear structure formation. Prior to
gravitational collapse, kinematical backreaction ($Q_D$) justifies this
approach in a Newtonian context. However, the final stages of a gravitational
collapse event are sudden; a globally imposed expansion rate thus forces at
least one expanding region to suddenly decelerate. This is relativistically
unrealistic. Instead, we allow non-collapsed domains to evolve in volume
according to the $Q_D$ Zel'dovich Approximation (QZA). We study the inferred
average expansion under this "silent" virialisation hypothesis. We set standard
(mpgrafic) EdS cosmological $N$-body initial conditions. Using RAMSES, we call
DTFE to estimate the initial values of the three invariants of the extrinsic
curvature tensor in Lagrangian domains $D$. We integrate the Raychaudhuri
equation in each domain using inhomog, adopt the stable clustering hypothesis
(VQZA), and average spatially. We adopt an early-epoch--normalised EdS
reference-model Hubble constant $H_1^{bg} = 37.7$ km/s/Mpc and an effective
Hubble constant $H_0^{eff} = 67.7$ km/s/Mpc. From 2000 simulations at
resolution $256^3$, a unity effective scale factor is reached at 13.8~Gyr (16%
above EdS) for an averaging scale of $L_{13.8}=2.5^{+0.1}_{-0.4}$
Mpc/$h^{eff}$. Relativistically interpreted, this corresponds to strong average
negative curvature evolution. The virialisation fraction and super-EdS
expansion correlate strongly at fixed cosmological time. Thus, starting from
EdS initial conditions and averaging on a typical non-linear structure
formation scale, the VQZA dark-energy--free average expansion matches
$\Lambda$CDM expansion to first order. The software packages used here are
free-licensed. |
Cosmic Distance Duality Relation and the Shape of Galaxy Clusters: Observations in the cosmological domain are heavily dependent on the validity
of the cosmic distance-duality (DD) relation, D_L(z) (1 + z)^{2}/D_{A}(z) = 1,
an exact result required by the Etherington reciprocity theorem where D_L(z)
and D_A(z) are, respectively, the luminosity and angular diameter distances. In
the limit of very small redshifts D_A(z) = D_L(z) and this ratio is trivially
satisfied. Measurements of Sunyaev-Zeldovich effect (SZE) and X-rays combined
with the DD relation have been used to determine D_A(z)from galaxy clusters.
This combination offers the possibility of testing the validity of the DD
relation, as well as determining which physical processes occur in galaxy
clusters via their shapes. We use WMAP (7 years) results by fixing the
conventional LCDM model to verify the consistence between the validity of DD
relation and different assumptions about galaxy cluster geometries usually
adopted in the literature. We assume that $\eta$ is a function of the redshift
parametrized by two different relations: \eta(z) = 1 + \eta_{0}z, and \eta(z)=1
+ \eta_{0}z/(1+z), where \eta_0 is a constant parameter quantifying the
possible departure from the strict validity of the DD relation. In order to
determine the probability density function (PDF) of \eta_{0}, we consider the
angular diameter distances from galaxy clusters recently studied by two
different groups by assuming elliptical (isothermal) and spherical
(non-isothermal) $\beta$ models. The strict validity of the DD relation will
occur only if the maximum value of \eta_{0} PDF is centered on \eta_{0}=0. It
was found that the elliptical $\beta$ model is in good agreement with the data,
showing no violation of the DD relation (PDF peaked close to \eta_0=0 at
1-sigma), while the spherical (non-isothermal) one is only marginally
compatible at 3-sigma. | PAHs as tracers of local AGN-Starburst connection: The main purpose of this research was to investigate how energetic processes
associated with Active Galactic Nuclei are related to those due to nuclear or
circumnuclear star formation activity. Photometric and spectroscopic data were
used to discriminate these processes in a sample of starburst, infrared
galaxies and AGNs. Herein, we propose new diagnostic diagrams based on the 7.7
{\mu}m polycyclic aromatic hydrocarbon emission band, the L(MIR, FIR) infrared
ratio and the q parameter. The diagnostic diagrams allow us to discriminate the
behavior of quasars and Seyfert 1-Seyfert 2 galaxies from starburst and
LIRGs-ULIRGs objects. |
CLMM: a LSST-DESC Cluster weak Lensing Mass Modeling library for
cosmology: We present the v1.0 release of CLMM, an open source Python library for the
estimation of the weak lensing masses of clusters of galaxies. CLMM is designed
as a standalone toolkit of building blocks to enable end-to-end analysis
pipeline validation for upcoming cluster cosmology analyses such as the ones
that will be performed by the LSST-DESC. Its purpose is to serve as a flexible,
easy-to-install and easy-to-use interface for both weak lensing simulators and
observers and can be applied to real and mock data to study the systematics
affecting weak lensing mass reconstruction. At the core of CLMM are routines to
model the weak lensing shear signal given the underlying mass distribution of
galaxy clusters and a set of data operations to prepare the corresponding data
vectors. The theoretical predictions rely on existing software, used as
backends in the code, that have been thoroughly tested and cross-checked.
Combined, theoretical predictions and data can be used to constrain the mass
distribution of galaxy clusters as demonstrated in a suite of example Jupyter
Notebooks shipped with the software and also available in the extensive online
documentation. | Three QSOs acting as strong gravitational lenses: We report the discovery of three new cases of QSOs acting as strong
gravitational lenses on background emission line galaxies: SDSS J0827+5224
(zQSO = 0.293, zs = 0.412), SDSS J0919+2720 (zQSO = 0.209, zs = 0.558), SDSS
J1005+4016 (zQSO = 0.230, zs = 0.441). The selection was carried out using a
sample of 22,298 SDSS spectra displaying at least four emission lines at a
redshift beyond that of the foreground QSO. The lensing nature is confirmed
from Keck imaging and spectroscopy, as well as from HST/WFC3 imaging in the
F475W and F814W filters. Two of the QSOs have face-on spiral host galaxies and
the third is a QSO+galaxy pair. The velocity dispersion of the host galaxies,
inferred from simple lens modeling, is between \sigma_v = 210 and 285 km/s,
making these host galaxies comparable in mass with the SLACS sample of
early-type strong lenses. |
The subtlety of Ly-a photons: changing the expected range of the 21-cm
signal: We present the evolution of the 21-cm signal from cosmic dawn and the epoch
of reionization (EoR) in an upgraded model including three subtle effects of
Ly-a radiation: Ly-a heating, CMB heating (mediated by Ly-a photons), and
multiple scattering of Ly-a photons. Taking these effects into account we
explore a wide range of astrophysical models and quantify the impact of these
processes on the global 21-cm signal and its power spectrum at observable
scales and redshifts. We find that, in agreement with the literature, Ly-a and
CMB heating raise the gas temperature by up to $\mathcal{O}(100)$ degrees in
models with weak X-ray heating and, thus, suppress the predicted 21-cm signals.
Varying the astrophysical parameters over broad ranges, we find that in the
upgraded model the absorption trough of the global signal reaches a lowest
floor of $-165$ mK at redshifts $z\approx 15-19$. This is in contrast with the
predictions for a pure adiabatically cooling Universe, for which the deepest
possible absorption is a monotonically decreasing function of cosmic time and
is $-178$ mK at $z = 19$ and $-216$ mK at $z=15$, dropping to even lower values
at lower redshifts (e.g. $-264$ mK at $z = 10$). With the Ly-a and CMB heating
included we also observe a strong suppression in the low-redshift power
spectra, with the maximum possible power (evaluated over the ensemble of
models) attenuated by a factor of $6.6$ at $z=9$ and $k = 0.1$ Mpc$^{-1}$.
Finally, we find that at high redshifts corresponding to cosmic dawn, the
heating terms have a subdominant effect while multiple scattering of Ly-a
photons is important, leading to an amplification of the power spectrum by a
factor of $\sim 2-5$. | Backreaction mechanism in multifluid and extended cosmologies: One possible explanation for the present observed acceleration of the
Universe is the breakdown of homogeneity and isotropy due to the formation of
non-linear structures. How inhomogeneities affect the averaged cosmological
expansion rate and lead to late-time acceleration is generally considered to be
due to some backreaction mechanism. General Relativity together with
pressure-free matter have until recently been considered as the sole
ingredients for averaged calculations. In this communication we focus our
attention on more general scenarios, including imperfect fluids as well as
alternative theories of gravity, and apply an averaging procedure to them in
order to determine possible backreaction effects. For illustrative purposes, we
present our results for dark energy models, quintessence and Brans-Dicke
theories. We also provide a discussion about the limitations of frame choices
in the averaging procedure. |
Nearby early-type galaxies with ionized gas.IV. Origin and powering
mechanism of the ionized gas: [ABRIDGED] With the aim of constraining the source of excitation and the
origin of the ionized gas in early-type galaxies (ETGs), we analyzed optical
spectra of a sample of 65 ETGs mostly located in low density environments.
Optical emission lines are detected in 89% of the sample. The incidence and
strength of emission do not correlate either with the E/S0 classification, or
with the fast/slow rotator classification. Comparing the nuclear r<r_e/16 line
emission with the classical [OIII]/Hb vs [NII]/Ha diagnostic diagram, the
galaxy activity is so classified: 72% are LINERs, 9% are Seyferts, 12% are
Composite/Transition objects, and 7% are non-classified. Seyferts have young
luminosity-weighted ages (<5 Gyr), and are significantly younger than LINERs
and Composites. Seyferts excluded, the spread in the ([OIII], Ha or [NII])
emission strength increases with the galaxy central velocity dispersion. The
[NII]/Ha ratio decreases with increasing galacto-centric distance, indicating
either a decrease of the nebular metallicity, or a progressive "softening" of
the ionizing spectrum. The average oxygen abundance of the ionized gas is
slightly less than solar, and a comparison with the results obtained in Paper
III from Lick indices reveals that it is ~0.2 dex lower than that of stars.
Conclusions: the nuclear emission can be explained with photoionization by PAGB
stars alone only in ~22% of the LINERs/Composite sample. On the other hand, we
can not exclude an important role of PAGB star photoionization at larger radii.
For the major fraction of the sample, the nuclear emission is consistent with
excitation from a low-accretion rate AGN, fast shocks (200 -500 km/s) in a
relatively gas-poor environment (n< 100 cm^-3), or coexistence of the two. The
derived nebular metallicities suggest either an external origin of the gas, or
an overestimate of the oxygen yields by SN models. | Detection of Quasar Feedback from the Thermal Sunyaev-Zel'dovich Effect
in Planck: Poorly understood feedback processes associated with highly-luminous black
hole accretion in quasars may dramatically affect the properties of their host
galaxies. We search for the effect of quasar feedback on surrounding gas using
Planck maps of the thermal Sunyaev-Zel'dovich effect (tSZ). By stacking tSZ
Compton-y maps centered on the locations of 26,686 spectroscopic quasars from
the Sloan Digital Sky Survey, we detect a strong but unresolved tSZ Compton-y
signal at >5 sigma significance that likely originates from a combination of
virialized halo atmosphere gas and quasar feedback effects. We show that the
feedback contribution to our detected quasar tSZ signal is likely to dominate
over virialized halo gas by isolating the feedback tSZ component for high- and
low-redshift quasars. We find that this quasar tSZ signal also scales with
black hole mass and bolometric luminosity, all consistent with general
expectations of quasar feedback. We estimate the mean angularly-integrated
Compton-y of quasars at z~1.5 to be 3.5x10^-6 Mpc^2, corresponding to mean
total thermal energies in feedback and virialized halo gas of 1.1(+/- 0.2) x
10^62 erg, and discuss the implications for quasar feedback. If confirmed, the
large total thermal feedback energetics we estimate of 5% (+/-1% statistical
uncertainty) of the black hole mass will have important implications for the
effects of quasar feedback on the host galaxy, as well as the surrounding
intergalactic medium. |
A gas-rich AGN near the centre of a galaxy cluster at z ~ 1.4: The formation of the first virialized structures in overdensities dates back
to ~9 Gyr ago, i.e. in the redshift range z ~ 1.4 - 1.6. Some models of
structure formation predict that the star formation activity in clusters was
high at that epoch, implying large reservoirs of cold molecular gas. Aiming at
finding a trace of this expected high molecular gas content in primeval
clusters, we searched for the 12CO(2-1) line emission in the most luminous
active galactic nucleus (AGN) of the cluster around the radio galaxy 7C
1756+6520 at z ~ 1.4, one of the farthest spectroscopic confirmed clusters.
This AGN, called AGN.1317, is located in the neighbourhood of the central radio
galaxy at a projected distance of ~780 kpc. The IRAM Plateau de Bure
Interferometer was used to investigate the molecular gas quantity in AGN.1317,
observing the 12CO(2-1) emission line. We detect CO emission in an AGN
belonging to a galaxy cluster at z ~ 1.4. We measured a molecular gas mass of
1.1 x 10^10 Msun, comparable to that found in submillimeter galaxies. In
optical images, AGN.1317 does not seem to be part of a galaxy interaction or
merger.We also derived the nearly instantaneous star formation rate (SFR) from
Halpha flux obtaining a SFR ~65 Msun/yr. This suggests that AGN.1317 is
actively forming stars and will exhaust its reservoir of cold gas in ~0.2-1.0
Gyr. | On Backreaction in Newtonian cosmology: We clarify that a result recently stated by Kaiser is contained in a theorem
of Buchert and Ehlers that is widely known for its main result: that there is
no global kinematical backreaction in Newtonian cosmology. Kaiser cites this
paper, re-derives parts of the theorem, but incompletely restates its content.
He makes further claims, which cannot be proven beyond the limited context of
Newtonian cosmology. We also discuss recent papers of R\'acz et al. and Roukema
who claim the existence of global backreaction within the Newtonian framework. |
An analytic approach to number counts of weak-lensing peak detections: We develop and apply an analytic method to predict peak counts in
weak-lensing surveys. It is based on the theory of Gaussian random fields and
suitable to quantify the level of spurious detections caused by chance
projections of large-scale structures as well as the shape and shot noise
contributed by the background galaxies. We compare our method to peak counts
obtained from numerical ray-tracing simulations and find good agreement at the
expected level. The number of peak detections depends substantially on the
shape and size of the filter applied to the gravitational shear field. Our main
results are that weak-lensing peak counts are dominated by spurious detections
up to signal-to-noise ratios of 3--5 and that most filters yield only a few
detections per square degree above this level, while a filter optimised for
suppressing large-scale structure noise returns up to an order of magnitude
more. | How an era of kination impacts substructure and the dark matter
annihilation rate: An era of kination occurs when the Universe's energy density is dominated by
a fast-rolling scalar field. Dark matter that is thermally produced during an
era of kination requires larger-than-canonical annihilation cross sections to
generate the observed dark matter relic abundance. Furthermore, dark matter
density perturbations that enter the horizon during an era of kination grow
linearly with the scale factor prior to radiation domination. We show how the
resulting enhancement to the small-scale matter power spectrum increases the
microhalo abundance and boosts the dark matter annihilation rate. We then use
gamma-ray observations to constrain thermal dark matter production during
kination. The annihilation boost factor depends on the minimum halo mass, which
is determined by the small-scale cutoff in the matter power spectrum.
Therefore, observational limits on the dark matter annihilation rate imply a
minimum cutoff scale for a given dark matter particle mass and kination
scenario. For dark matter that was once in thermal equilibrium with the
Standard Model, this constraint establishes a maximum allowed kinetic
decoupling temperature for the dark matter. This bound on the decoupling
temperature implies that the growth of perturbations during kination cannot
appreciably boost the dark matter annihilation rate if dark matter was once in
thermal equilibrium with the Standard Model. |
The 3-5 micron Spectrum of NGC 1068 at High Angular Resolution:
Distribution of Emission and Absorption Features across the Nuclear Continuum
Source: We report moderate resolution 3-5 micron spectroscopy of the nucleus of NGC
1068 obtained at 0.3 arcsec (20 pc) resolution with the spectrograph slit
aligned approximately along the ionization cones of the AGN. The deconvolved
FWHM of the nuclear continuum source in this direction is 0.3 arcsec. Four
coronal lines of widely different excitations were detected; the intensity of
each peaks near radio knot C, approximately 0.3 arcsec north of the infrared
continuum peak, where the radio jet changes direction. Together with the
broadened line profiles observed near that location, this suggests that
shock-ionization is the dominant excitation mechanism of the coronal lines. The
depth of the 3.4 micron hydrocarbon absorption is maximum at and just south of
the continuum peak, similar to the 10 micron silicate absorption. That and the
similar and rapid variations of the optical depths of both features across the
nucleus suggest that substantial portions of both arise in a dusty environment
just in front of the continuum source(s). A new and tighter limit is set on the
column density of CO. Although clumpy models of the dust screen might explain
the shallowness of the silicate feature, the presence of the 3.4 micron feature
and the absence of CO are strongly reminiscent of Galactic diffuse cloud
environments and a consistent explanation for them and the observed silicate
feature is found if all three phenomena occur in such an environment, existing
as close as 10 pc from the central engine. | Cosmological constraints on extended Galileon models: The extended Galileon models possess tracker solutions with de Sitter
attractors along which the dark energy equation of state is constant during the
matter-dominated epoch, i.e. w_DE = -1-s, where s is a positive constant. Even
with this phantom equation of state there are viable parameter spaces in which
the ghosts and Laplacian instabilities are absent. Using the observational data
of the supernovae type Ia, the cosmic microwave background (CMB), and baryon
acoustic oscillations, we place constraints on the tracker solutions at the
background level and find that the parameter s is constrained to be s=0.034
(-0.034,+0.327) (95% CL) in the flat Universe. In order to break the degeneracy
between the models we also study the evolution of cosmological density
perturbations relevant to the large-scale structure (LSS) and the
Integrated-Sachs-Wolfe (ISW) effect in CMB. We show that, depending on the
model parameters, the LSS and the ISW effect is either positively or negatively
correlated. It is then possible to constrain viable parameter spaces further
from the observational data of the ISW-LSS cross-correlation as well as from
the matter power spectrum. |
Impact of inhomogeneous reionization on post-reionization 21 cm
intensity mapping measurement of cosmological parameters: 21 cm intensity mapping (IM) has the potential to be a strong and unique
probe of cosmology from redshift of order unity to redshift potentially as high
as 30. For post-reionization 21 cm observations, the signal is modulated by the
thermal and dynamical reaction of gas in the galaxies to the passage of
ionization fronts during the Epoch of Reionization. In this work, we
investigate the impact of inhomogeneous reionization on the post-reionization
21 cm power spectrum and the induced shifts of cosmological parameters at
redshifts $3.5 \lesssim z \lesssim 5.5$. We make use of hydrodynamics
simulations that could resolve small-scale baryonic structure evolution to
quantify HI abundance fluctuation, while semi-numerical large box 21cmFAST
simulations capable of displaying inhomogeneous reionization process are
deployed to track the inhomogeneous evolution of reionization bubbles. We
discussed the prospects of capturing this effect in two post-reionization 21 cm
intensity mapping experiments: SKA1-LOW and PUMA. We find the inhomogeneous
reionization effect could impact the HI power spectrum up to tens of percent
level and shift cosmological parameters estimation from sub-percent to tens
percent in the observation of future post-reionization 21 cm intensity mapping
experiments such as PUMA, while SKA1-LOW is likely to miss this effect at the
redshifts of interest given the considered configuration. In particular, the
shift is up to 0.0206 in the spectral index $n_s$ and 0.0192 eV in the sum of
the neutrino masses $\sum m_\nu$ depending on the reionization model and the
observational parameters. We discuss strategies to mitigate and separate these
biases. | Testing coupled dark energy with large scale structure observation: The coupling between the dark components provides a new approach to mitigate
the coincidence problem of cosmological standard model. In this paper, dark
energy is treated as a fluid with a constant equation of state, whose coupling
with dark matter is $\bar{Q}=3H\xi_x\bar{\rho}_x$. In the frame of dark energy,
we derive the evolution equations for the density and velocity perturbations.
According to the Markov Chain Monte Carlo method, we constrain the model by
currently available cosmic observations which include cosmic microwave
background radiation, baryon acoustic oscillation, type Ia supernovae, and
$f\sigma_8(z)$ data points from redshift-space distortion. The results show the
interaction rate in 3$\sigma$ regions:
$\xi_x=0.00328_{-0.00328-0.00328-0.00328}^{+0.000736+0.00549+0.00816}$, which
means that the recently cosmic observations favor a small interaction rate
which is up to the order of $10^{-2}$, meanwhile, the measurement of
redshift-space distortion could rule out the large interaction rate in the
1$\sigma$ region. |
The Origin of the 4.5 micron Excess from Dwarf Galaxies: Dwarf galaxies tend to have redder [3.6 micron] - [4.5 micron] Spitzer
broadband colors than spirals. To investigate this effect, for a large sample
of dwarf galaxies we combine Spitzer fluxes with data at other wavelengths and
compare to population synthesis models. Lower metallicity systems are found to
have redder [3.6] - [4.5] colors on average, but with considerable scatter. The
observed range in [3.6] - [4.5] color is too large to be accounted for solely
by variations in stellar colors due to age or metallicity differences;
interstellar effects must contribute as well. For the reddest systems, the 4.5
micron luminosity may not be a good tracer of stellar mass. We identify three
factors that redden this color in dwarfs. First, in some systems, strong
Br-alpha emission contributes significantly to the 4.5 micron emission. Second,
in some cases high optical depths lead to strong reddening of the starlight in
the Spitzer bands. Third, in some galaxies, the nebular continuum dominates the
4.5 micron flux, and in extreme cases, the 3.6 micron flux as well. The harder
UV radiation fields in lower metallicity systems produce both more gaseous
continuum in the infrared and more Br-alpha per star formation rate. The
combination of these three factors can account for the 4.5 micron excess in our
sample galaxies, thus it is not necessary to invoke a major contribution from
hot dust to the 4.5 micron band. However, given the uncertainties, we are not
able to completely rule out hot dust emission at 4.5 micron. More spectroscopic
observations in the 3 - 5 micron range are needed to disentangle these effects. | Gravitational redshifting of galaxies in the SPIDERS cluster catalogue: Data from the SPectroscopic IDentification of ERosita Sources (SPIDERS) are
searched for a detection of the gravitational redshifting of light from
$\sim\!20\,000$ galaxies in $\sim\!2500$ galaxy clusters using three
definitions of the cluster centre: its Brightest Cluster Galaxy (BCG), the
redMaPPer identified Central Galaxy (CG), or the peak of X-ray emission.
Distributions of velocity offsets between galaxies and their host cluster's
centre, found using observed redshifts, are created. The quantity
$\hat{\Delta}$, the average of the radial velocity difference between the
cluster members and the cluster systemic velocity, reveals information on the
size of a combination of effects on the observed redshift, dominated by
gravitational redshifting. The change of $\hat{\Delta}$ with radial distance is
predicted for SPIDERS galaxies in General Relativity (GR), and $f(R)$ gravity,
and compared to the observations. The values of $\hat{\Delta}=-13.5\pm4.7$ km
s$^{-1}$, $\hat{\Delta}=-12.5\pm5.1$ km s$^{-1}$, and
$\hat{\Delta}=-18.6\pm4.8$ km s$^{-1}$ for the BCG, X-ray and CG cases
respectively broadly agree with the literature. There is no significant
preference of one gravity theory over another, but all cases give a clear
detection ($>2.5\sigma$) of $\hat{\Delta}$. The BCG centroid is deemed to be
the most robust method in this analysis, due to no well defined central
redshift when using an X-ray centroid, and CGs identified by redMaPPer with no
associated spectroscopic redshift. For future gravitational redshift studies,
an order of magnitude more galaxies, $\sim\!500\,000$, will be required-a
possible feat with the forthcoming Vera C. Rubin Observatory, Euclid and
eROSITA. |
CosmicNet II: Emulating extended cosmologies with efficient and accurate
neural networks: In modern analysis pipelines, Einstein-Boltzmann Solvers (EBSs) are an
invaluable tool for obtaining CMB and matter power spectra. To accelerate the
computation of these observables, the CosmicNet strategy is to replace the
bottleneck of an EBS, which is the integration of a system of differential
equations for linear cosmological perturbations, by neural networks. This
strategy offers advantages compared to the direct emulation of the final
observables, including small networks that are easy to train in
high-dimensional parameter spaces, and which do not depend by on primordial
spectrum parameters nor observation-related quantities such as selection
functions. In this second CosmicNet paper, we present a more efficient set of
networks that are already trained for extended cosmologies beyond LCDM, with
massive neutrinos, extra relativistic degrees of freedom, spatial curvature,
and dynamical dark energy. We release a new branch of the CLASS code, called
CLASSNET, which automatically uses networks within a region of trusted
accuracy. We demonstrate the accuracy and performance of CLASSNET by presenting
parameter inference runs from Planck, BAO and supernovae data, performed with
CLASSNET and the COBAYA inference package. We have eliminated the perturbation
module as a bottleneck of the EBS, with a speedup that is even more remarkable
in extended cosmologies, where the usual approach would have been more
expensive while the network's performance remains the same. We obtain a speedup
factor of order 150 for the emulated perturbation module of CLASS. For the
whole code, this translates into an overall speedup factor of order 3 when
computing CMB harmonic spectra (now dominated by the highly parallelizable and
further optimizable line-of-sight integration), and of order 50 when computing
matter power spectra (less than 0.1 seconds even in extended cosmologies). | First observational constraints on tensor non-Gaussianity sourced by
primordial magnetic fields from cosmic microwave background: Primordial magnetic fields (PMFs) create a large squeezed-type
non-Gaussianity in tensor perturbation, which generates non-Gaussian
temperature fluctuations in the cosmic microwave background (CMB). We for the
first time derive an observational constraint on such a tensor non-Gaussianity
from observed CMB maps. Analyzing temperature maps of the WMAP 7-year data, we
find that such a tensor non-Gaussianity is consistent with zero. This gives an
upper bound on PMF strength smoothed on $1 ~ {\rm Mpc}$ as $B_{1 ~ \rm Mpc} <
3.1 ~{\rm nG}$ at $95%$ C.L. |
The Extended GMRT Radio Halo Survey I: New upper limits on radio halos
and mini-halos: A fraction of galaxy clusters host diffuse radio sources called radio halos,
radio relics and mini-halos. We present the sample and first results from the
Extended GMRT Radio Halo Survey (EGRHS)- an extension of the GMRT Radio Halo
Survey (GRHS, Venturi et al. 2007, 2008). It is a systematic radio survey of
galaxy clusters selected from the REFLEX and eBCS X-ray catalogs . Analysis of
GMRT data at 610/ 235/ 325 MHz on 12 galaxy clusters are presented. We report
the detection of a newly discovered mini-halo in the cluster RXJ1532.9+3021 at
610 MHz. A small scale relic (~200 kpc) is suspected in the cluster Z348. We do
not detect cluster-scale diffuse emission in 11 clusters. Robust upper limits
on the detection of radio halo of size of 1 Mpc are determined. We also present
upper limits on the detections of mini-halos in a sub-sample of cool-core
clusters. The upper limits for radio halos and mini-halos are plotted in the
radio power- X-ray luminosity plane and the correlations are discussed. Diffuse
extended emission, not related to the target clusters, but detected as
by-products in the sensitive images of two of the cluster fields (A689 and
RXJ0439.0+0715) are reported. Based on the information about the presence of
radio halos (or upper limits), available on 48 clusters out of the total sample
of 67 clusters (EGRHS+GRHS), we find that ~23% of the clusters host radio
halos. The radio halo fraction rises to ~31%, when only the clusters with X-ray
luminosities >8x10^44 erg/s are considered. Mini-halos are found in ~50 % of
cool-core clusters. A qualitative examination of the X-ray images of the
clusters with no diffuse radio emission indicates that a majority of these
clusters do not show extreme dynamical disturbances and supports the idea that
mergers play an important role in the generation of radio halos/relics. | Inflection point inflation: WMAP constraints and a solution to the
fine-tuning problem: We consider observational constraints and fine-tuning issues in a
renormalizable model of inflection point inflation, with two independent
parameters. We derive constraints on the parameter space of this model arising
from the WMAP 7-year power spectrum. It has previously been shown that it is
possible to successfully embed this potential in the MSSM. Unfortunately, to do
this requires severe fine-tuning. We address this issue by introducing a hybrid
field to dynamically uplift the potential with a subsequent smooth phase
transition to end inflation at the necessary point. Large parameter regions
exist where this drastically reduces the fine-tuning required without ruining
the viability of the model. A side effect of this mechanism is that it
increases the width of the slow-roll region of the potential, thus also
alleviating the problem of the fine-tuning of initial conditions. The MSSM
embedding we study has been previously shown to be able to explain the
smallness of the neutrino masses. The hybrid transition does not spoil this
feature as there exist parameter regions where the fine-tuning parameter is as
large as $10^{-1}$ and the neutrino masses remain small. |
Particle Dark Matter: Status and Searches: A brief overview is given of the phenomenology of particle dark matter and
the properties of some of the most widely studied dark matter candidates.
Recent developments in direct and indirect dark matter searches are discussed. | Light path averages in spacetimes with non-vanishing average spatial
curvature: Effects of inhomogeneities on observations have been vastly studied using
both perturbative methods, N-body simulations and Swiss cheese solutions to the
Einstein equations. In nearly all cases, such studied setups assume vanishing
spatial background curvature. While a spatially flat
Friedmann-Lemaitre-Robertson-Walker model is in accordance with observations, a
non-vanishing curvature is not ruled out. It is therefore important to note
that, as has been pointed out in the literature, 1 dimensional averages might
not converge to volume averages in non-Euclidean space. If this is indeed the
case, it will affect the interpretation of observations in spacetimes with
non-vanishing average spatial curvature. This possibility is therefore studied
here by computing the integrated expansion rate and shear, the accumulated
density contrast, and fluctuations in the redshift-distance relation in Swiss
cheese models with different background curvatures. It is found that
differences in mean and dispersion of these quantities in the different models
are small and naturally attributable to differences in background expansion
rate and density contrasts. Thus, the study does not yield an indication that
the relationship between 1 dimensional spatial averages and volume averages
depends significantly on background curvature. |
Incidence of Mg II absorption systems towards flat-spectrum radio
quasars: The conventional wisdom that the rate of incidence of Mg II absorption
systems, dN/dz (excluding `associated systems' having velocity beta*c relative
to the AGN of less than ~5000 km/s) is totally independent of the background
AGN, has been challenged by a recent finding that dN/dz for strong Mg II
absorption systems towards distant blazars is 2.2 \pm_{0.6}^{0.8} times the
value known for normal optically-selected quasars (QSOs). This has led to the
suggestion that a significant fraction of even the absorption systems with beta
as high as 0.1 may have been ejected by the relativistic jets in the blazars,
which are expected to be pointed close to our direction. Here we investigate
this scenario using a large sample of 115 flat-spectrum radio-loud quasars
(FSRQs) which too possess powerful jets, but are only weakly polarized. We
show, for the first time, that dN/dz towards FSRQs is, on the whole, quite
similar to that known for QSOs and the comparative excess of strong \mgii
absorption systems seen towards blazars is mainly confined to beta< 0.15. The
excess relative to FSRQs can probably result from a likely closer alignment of
blazar jets with our direction and hence any gas clouds accelerated by them are
more likely to be on the line of sight to the active quasar nucleus. | The effects of flattening and rotation on the temperature of the X-ray
halos of elliptical galaxies: Elliptical galaxies have hot coronae with X-ray luminosities and mean gas
temperatures that span over wide ranges. This variation can be partially due to
the energy budget of the hot gas, that depends on the host galaxy structure and
internal kinematics. With the aid of realistic axisymmetric galaxy models, we
performed a diagnostic study focussed on the effects of galaxy flattening and
rotational support on the hot gas temperature. |
Fundamental properties of Fanaroff-Riley II radio galaxies investigated
via Monte Carlo simulations: [Abridged] Radio galaxies and quasars are among the largest and most powerful
single objects known and are believed to have had a significant impact on the
evolving Universe and its large scale structure. We explore the intrinsic and
extrinsic properties of the population of FRII objects (kinetic luminosities,
lifetimes, and the central densities of their environments). In particular, the
radio and kinetic luminosity functions of FRIIs are investigated using the
complete, flux limited radio catalogues of 3CRR and Best et al. We construct
multidimensional Monte Carlo simulations using semi-analytical models of FRII
radio source growth to create artificial samples of radio galaxies. Unlike
previous studies, we compare radio luminosity functions found with both the
observed and simulated data to explore the fundamental source parameters. We
allow the source physical properties to co-evolve with redshift, and we find
that all the investigated parameters most likely undergo cosmological
evolution. Strikingly, we find that the break in the kinetic luminosity
function must undergo redshift evolution of at least (1+z)^3. The fundamental
parameters are strongly degenerate, and independent constraints are necessary
to draw more precise conclusions. We use the estimated kinetic luminosity
functions to set constraints on the duty cycles of these powerful radio
sources. A comparison of the duty cycles of powerful FRIIs with those
determined from radiative luminosities of AGN of comparable black hole mass
suggests a transition in behaviour from high to low redshifts, corresponding to
either a drop in the typical black hole mass of powerful FRIIs at low
redshifts, or a transition to a kinetically-dominated, radiatively-inefficient
FRII population. | Testing the consistency between cosmological data: the impact of spatial
curvature and the dark energy EoS: The results of joint analyses of available cosmological data have motivated
an important debate about a possible detection of a non-zero spatial curvature.
If confirmed, such a result would imply a change in our present understanding
of cosmic evolution with important theoretical and observational consequences.
In this paper we discuss the legitimacy of carrying out joint analyses with the
currently available data sets and explore their implications for a non-flat
universe and extensions of the standard cosmological model. We use a robust
tension estimator to perform a quantitative analysis of the physical
consistency between the latest data of Cosmic Microwave Background, type Ia
supernovae, Baryonic Acoustic Oscillations and Cosmic Chronometers. We consider
the flat and non-flat cases of the $\Lambda$CDM cosmology and of two dark
energy models with a constant and varying dark energy EoS parameter. The
present study allows us to better understand if possible inconsistencies
between these data sets are significant enough to make the results of their
joint analyses misleading, as well as the actual dependence of such results
with the spatial curvature and dark energy parameterizations. |
Probing the Star Formation History and Initial Mass Function of the
z~2.5 Lensed Galaxy SMM J163554.2+661225 with Herschel: We present the analysis of Herschel SPIRE far-infrared (FIR) observations of
the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and
500 micron observations with existing data, we make an improved fit to the FIR
spectral energy distribution (SED) of this galaxy. We find a total infrared
(IR) luminosity of L(8--1000 micron) = 6.9 +/- 0.6x10^11 Lsol; a factor of 3
more precise over previous L_IR estimates for this galaxy, and one of the most
accurate measurements for any galaxy at these redshifts. This FIR luminosity
implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10
Msol per yr, which is a factor of 1.9 +/- 0.35 lower than the SFR derived from
the nebular Pa-alpha emission line (a 2.5-sigma discrepancy). Both SFR
indicators assume identical Salpeter initial mass functions (IMF) with slope
Gamma=2.35 over a mass range of 0.1 - 100 Msol, thus this discrepancy suggests
that more ionizing photons may be necessary to account for the higher
Pa-alpha-derived SFR. We examine a number of scenarios and find that the
observations can be explained with a varying star formation history (SFH) due
to an increasing star formation rate (SFR), paired with a slight flattening of
the IMF. If the SFR is constant in time, then larger changes need to be made to
the IMF by either increasing the upper-mass cutoff to ~ 200 Msol, or a
flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These
scenarios result in up to double the number of stars with masses above 20 Msol,
which produce the requisite increase in ionizing photons over a Salpeter IMF
with a constant SFH. | Hubble constant and dark energy inferred from free-form determined time
delay distances: Time delays between multiple images of lensed sources can probe the geometry
of the universe. We propose a novel method based on free-form modelling of
gravitational lenses to estimate time-delay distances and, in turn,
cosmological parameters. This approach does not suffer from the degeneracy
between the steepness of the profile and the cosmological parameters. We apply
the method to 18 systems having time delay measurements and find
H_0=69+-6(stat.)+-4(syst.) km s^{-1}Mpc^{-1}. In combination with WMAP9, the
constraints on dark energy are Omega_w=0.68+-0.05 and w=-0.86+-0.17 in a flat
model with constant equation-of-state. |
Cosmological Forecast of the Void Size Function Measurement from the
CSST Spectroscopic Survey: Void size function (VSF) contains the information of the cosmic large-scale
structure (LSS), and can be used to derive the properties of dark energy and
dark matter. We predict the VSFs measured from the spectroscopic galaxy survey
operated by the China Space Station Telescope (CSST), and study the strength of
cosmological constraint. We employ a high-resolution Jiutian simulation to get
galaxy samples based on an improved semi-analytical model, and then generate a
mock galaxy catalog of the CSST spectroscopic survey according to the detection
sensitivity. We identify voids from this galaxy catalog using the watershed
algorithm without assuming a spherical shape, and estimate the VSFs at
different redshift bins from $z=0.5$ to 1.1. To obtain a reliable and accurate
fitting result, we propose a void selection method based on the ellipticity,
for comparing to the theoretical model with a linear underdensity threshold of
void formation $\delta_{\rm v}$ assuming the spherical evolution. We assume
$\delta_{\rm v}$ is redshift-dependent and set it as a free parameter in each
redshift bin. The Markov Chain Monte Carlo (MCMC) method is adopted to
implement the constraints on the cosmological and void parameters. We find that
the VSFs from the selected voids can be well fitted by the theoretical model,
and could accurately reserve the cosmological information. Based on our
estimation, the VSF measurement of the CSST spectroscopic survey can constrain
the cosmological parameters to a few percent level. The best-fit values of
$\delta_{\rm v}$ are ranging from $\sim-0.4$ to $-0.1$ as the redshift
increases from 0.5 to 1.1, which has a distinct difference from the theoretical
calculation with a constant $\delta_{\rm v}\simeq-2.7$ assuming the spherical
evolution. Our method can provide a good reference for void identification and
selection in the VSF analysis of the spectroscopic galaxy surveys. | Deep Learning nearby galaxy peculiar velocities: We explore how information in images of nearby galaxies can be used to
estimate their distance. We train a convolutional Neural Network (NN) to do
this, using galaxy images from the Illustris simulation. We show that if the NN
is trained on data with random errors added to the true distance (representing
training using spectroscopic redshift instead of actual distance), then the NN
can predict distances in a test dataset with greater accuracy than it was given
in the training set. This is not unusual, as often NNs are trained on data with
added noise, in order to increase robustness. In this case, however, it offers
a route to estimating peculiar velocities of nearby galaxies. Given a galaxy
with a known spectroscopic redshift one can use the NN-predicted distance to
make an estimate of the peculiar velocity. Trying this using relatively low
resolution (1.4 arcsec per pixel) simulated galaxy images we find fractional
RMS distance errors of 7.7% for galaxies at a mean distance of 75 Mpc from the
observer, leading to RMS peculiar velocity errors of 440 km/s. In a companion
paper we apply the technique to 145,115 nearby galaxies from the NASA Sloan
Atlas. |
Constraints on the Combined Models with $R^{2-q}$ Inflation and Viable
$f(R)$ Dark Energy: We investigate the observational constraints on the modified gravity, which
combines the $R^{2-q}$ inflation with the power-law (exponential) type of the
viable $f(R)$ dark energy models. We discuss the difference between the
combined model and $R^{2-q}$ gravity in the inflationary epoch and obtain the
constraints on the deviation power $q$ as well as the parameters in $f(R)$ by
using the CosmoMC package. The allowed ranges of the spectral index and
tensor-to-scalar ratio from the Planck data are highly restricted, resulting in
$q < 2.66 \times 10^{-2}$ and $2.17 \times 10^{-2}$ for the power-law and
exponential types of $f(R)$ gravity, respectively. | Neutrino physics and precision cosmology: I review the current status of structure formation bounds on neutrino
properties such as mass and energy density. I also discuss future cosmological
bounds as well as a variety of different scenarios for reconciling cosmology
with the presence of light sterile neutrinos. |
Modeling very long baseline interferometric images with the
cross-entropy global optimization technique: We present a new technique for obtaining model fittings to VLBI images of
astrophysical jets. The method minimizes a performance function proportional to
the sum of the squared difference between the model and observed images. The
model image is constructed by summing elliptical Gaussian sources characterized
by six parameters: two-dimensional peak position, peak intensity, eccentricity,
amplitude and orientation angle of the major axis. We present results for the
fitting of two main benchmark jets: the first, constructed from three
individual Gaussian sources, the second formed by five Gaussian sources. Both
jets were analyzed by our cross-entropy technique in finite and infinite
signal-to-noise regimes, the background noise chosen to mimic that found in
interferometric radio maps. We show that our technique is capable of recovering
the parameters of the sources with a similar accuracy to that obtained from the
traditional AIPS task IMFIT when the image is relatively simple (e.g., few
components). For more complex maps, our method displays superior performance in
recovering the parameters of the jet components. Our methodology is also able
to show quantitatively the number of individual components present in an image.
An additional application of the cross-entropy technique to a real image of a
BL Lac object is shown and discussed. Our results indicate that our
cross-entropy technique must be used in situations involving the analysis of
complex emission regions having more than three sources, even though it is
substantially slower than current model fitting tasks (at least 10,000 times
slower for a single processor, depending on the number of sources to be
optimized). As in the case of any model fitting performed in the image plane,
caution is required in analyzing images constructed from a poorly sampled (u,v)
plane. | MESMER: MeerKAT Search for Molecules in the Epoch of Reionization: [Abridged] Observations of molecular gas at all redshifts are critical for
measuring the cosmic evolution in molecular gas density and understanding the
star-formation history of the Universe. The 12CO molecule (J=1-0 transition =
115.27 GHz) is the best proxy for extragalactic H2, which is the gas reservoir
from which star formation occurs, and has been detected out to z~6. Typically,
redshifted high-J lines are observed at mm-wavelengths, the most commonly
targeted systems exhibiting high SFRs (e.g. submm galaxies), and far-IR-bright
QSOs. While the most luminous objects are the most readily observed, detections
of more typical galaxies with modest SFRs are essential for completing the
picture. ALMA will be revolutionary in terms of increasing the detection rate
and pushing the sensitivity limit down to include such galaxies, however the
limited FoV when observing at such high frequencies makes it difficult to use
ALMA for studies of the large-scale structure traced out by molecular gas in
galaxies. This article introduces a strategy for a systematic search for
molecular gas during the EoR (z~7 and above), capitalizing on the fact that the
J=1-0 transition of 12CO enters the upper bands of cm-wave instruments at
high-z. The FoV advantage gained by observing at such frequencies, coupled with
modern broadband correlators allows significant cosmological volumes to be
probed on reasonable timescales. In this article we present an overview of our
future observing programme which has been awarded 6,500 hours as one of the
Large Survey Projects for MeerKAT, the forthcoming South African SKA pathfinder
instrument. Its large FoV and correlator bandwidth, and high-sensitivity
provide unprecedented survey speed for such work. An existing astrophysical
simulation is coupled with instrumental considerations to demonstrate the
feasibility of such observations and predict detection rates. |
A sample of small size compact steep-spectrum radio sources. VLBI images
and VLA polarization at 5 GHz: Global VLBI observations at 5 GHz have been performed to study the source
morphology in 10 compact steep-spectrum (CSS) sources selected from the Peacock
& Wall catalogue with the aim of finding asymmetric structures produced by the
interaction with the ambient medium. The combination of these data and earlier
1.7-GHz observations allows the study of the spectral index distribution across
the source structure and the unambiguous determination of the nature of each
component. In seven sources we detected the core component with a flat or
inverted spectrum. In six sources the radio emission has a two-sided morphology
and comes mainly from steep-spectrum extended structures, like lobes, jets, and
hotspots. Only one source, 0319+121, has a one-sided core-jet structure. In
three out of the six sources with a two-sided structure the flux density
arising from the lobes is asymmetric, and the brightest lobe is the one closest
to the core, suggesting that the jets are expanding in an inhomogeneous ambient
medium which may influence the source growth. The interaction between the jet
and the environment may slow down the source expansion and enhance the
luminosity due to severe radiative losses, likely producing an excess of CSS
radio sources in flux density limited samples. The lobes of the other three
asymmetric sources have a brighter-when-farther behaviour, in agreement with
what is expected by projection and relativistic effects. Simultaneous VLA
observations carried out to investigate the polarization properties of the
targets detected significant polarized emission (~5.5%) only from the quasar
0319+121. | What Determines the Incidence and Extent of MgII Absorbing Gas Around
Galaxies?: We study the connections between on-going star formation, galaxy mass, and
extended halo gas, in order to distinguish between starburst-driven outflows
and infalling clouds that produce the majority of observed MgII absorbers at
large galactic radii (>~ 10 h^{-1} kpc) and to gain insights into halo gas
contents around galaxies. We present new measurements of total stellar mass
(M_star), H-alpha emission line strength (EW(H-alpha)), and specific star
formation rate (sSFR) for the 94 galaxies published in H.-W. Chen et al.
(2010). We find that the extent of MgII absorbing gas, R_MgII, scales with
M_star and sSFR, following R_MgII \propto M_star^{0.28}\times sSFR^{0.11}. The
strong dependence of R_MgII on M_star is most naturally explained, if more
massive galaxies possess more extended halos of cool gas and the observed MgII
absorbers arise in infalling clouds which will subsequently fuel star formation
in the galaxies. The additional scaling relation of R_MgII with sSFR can be
understood either as accounting for extra gas supplies due to starburst
outflows or as correcting for suppressed cool gas content in high-mass halos.
The latter is motivated by the well-known sSFR--M_star} inverse correlation in
field galaxies. Our analysis shows that a joint study of galaxies and MgII
absorbers along common sightlines provides an empirical characterization of
halo gaseous radius versus halo mass. A comparison study of R_MgII around red-
and blue-sequence galaxies may provide the first empirical constraint for
resolving the physical origin of the observed sSFR--M_star} relation in
galaxies. |
Gravitational recoils of supermassive black holes in hydrodynamical
simulations of gas rich galaxies: We study the evolution of gravitationally recoiled supermassive black holes
(BHs) in massive gas-rich galaxies by means of high-resolution hydrodynamical
simulations. We find that the presence of a massive gaseous disc allows
recoiled BHs to return to the centre on a much shorter timescale than for
purely stellar discs. Also, BH accretion and feedback can strongly modify the
orbit of recoiled BHs and hence their return timescale, besides affecting the
distribution of gas and stars in the galactic centre. However, the dynamical
interaction of kicked BHs with the surrounding medium is in general complex and
can facilitate both a fast return to the centre as well as a significant delay.
The Bondi-Hoyle-Lyttleton accretion rates of the recoiling BHs in our simulated
galaxies are favourably high for the detection of off-centred AGN if kicked
within gas-rich discs -- up to a few per cent of the Eddington accretion rate
-- and are highly variable on timescales of a few 10^7 yrs. In major merger
simulations of gas-rich galaxies, we find that gravitational recoils increase
the scatter in the BH mass -- host galaxy relationships compared to simulations
without kicks, with the BH mass being more sensitive to recoil kicks than the
bulge mass. A generic result of our numerical models is that the clumpy massive
discs suggested by recent high-redshift observations, as well as the remnants
of gas-rich mergers, exhibit a gravitational potential that falls steeply in
the central regions, due to the dissipative concentration of baryons. As a
result, supermassive BHs should only rarely be able to escape from massive
galaxies at high redshifts, which is the epoch where the bulk of BH recoils is
expected to occur.[Abridged] | SHARP -- VII. New constraints on the dark matter free-streaming
properties and substructure abundance from gravitationally lensed quasars: We present an analysis of seven strongly gravitationally lensed quasars and
the corresponding constraints on the properties of dark matter. Our results are
derived by modelling the lensed image positions and flux-ratios using a
combination of smooth macro models and a population of low-mass haloes within
the mass range 10^6 to 10^9 Msun. Our lens models explicitly include
higher-order complexity in the form of stellar discs and luminous satellites,
as well as low-mass haloes located along the observed lines of sight for the
first time. Assuming a Cold Dark Matter (CDM) cosmology, we infer an average
total mass fraction in substructure of f_sub = 0.012^{+0.007}_{-0.004} (68 per
cent confidence limits), which is in agreement with the predictions from CDM
hydrodynamical simulations to within 1 sigma. This result is closer to the
predictions than those from previous studies that did not include line-of-sight
haloes. Under the assumption of a thermal relic dark matter model, we derive a
lower limit on the particle relic mass of m th > 5.58 keV (95 per cent
confidence limits), which is consistent with a value of m_th > 5.3 keV from the
recent analysis of the Ly-alpha forest. We also identify two main sources of
possible systematic errors and conclude that deeper investigations in the
complex structure of lens galaxies as well as the size of the background
sources should be a priority for this field. |
The Lack of Non-Thermal Motions in Galaxy Cluster Cores: We report the non-thermal pressure fraction (Pnt/Ptot) obtained from a
three-dimensional triaxial analysis of 16 galaxy clusters in the CLASH sample
using gravitational lensing (GL) data primarily from Subaru and HST, X-ray
spectroscopic imaging from Chandra, and Sunyaev-Zel'dovich effect (SZE) data
from Planck and Bolocam. Our results span the approximate radial range
0.015-0.4R200m (35-1000 kpc). At cluster-centric radii smaller than 0.1R200m
the ensemble average Pnt/Ptot is consistent with zero with an upper limit of
nine per cent, indicating that heating from active galactic nuclei and other
relevant processes does not produce significant deviations from hydrostatic
equilibrium (HSE). The ensemble average Pnt/Ptot increases outside of this
radius to approximately 20 per cent at 0.4R200m, as expected from simulations,
due to newly accreted material thermalizing via a series of shocks. Also in
agreement with simulations, we find significant cluster-to-cluster variation in
Pnt/Ptot and little difference in the ensemble average Pnt/Ptot based on
dynamical state. We conclude that on average, even for diverse samples,
HSE-derived masses in the very central regions of galaxy clusters require only
modest corrections due to non-thermal motions. | The Brightest of Reionizing Galaxies (BoRG) survey: Until now, investigating the early stages of galaxy formation has been
primarily the realm of theoretical modeling and computer simulations, which
require many physical ingredients and are challenging to test observationally.
However, the latest Hubble Space Telescope observations in the near infrared
are shedding new light on the properties of galaxies within the first billion
years after the Big Bang, including our recent discovery of the most distant
proto-cluster of galaxies at redshift z~8. Here, I compare predictions from
models of primordial and metal-enriched star formation during the dark ages
with the latest Hubble observations of galaxies during the epoch of
reionization. I focus in particular on the luminosity function and on galaxy
clustering as measured from our Hubble Space Telescope Brightest of Reionizing
Galaxies (BoRG) survey. BoRG has the largest area coverage to find luminous and
rare z~8 sources that are among the first galaxies to have formed in the
Universe. |
An optical and HI study of the dwarf Local Group galaxy VV124=UGC4879. A
gas-poor dwarf with a stellar disk?: We present a detailed study of the dwarf galaxy VV124, recently recognized as
a isolated member of the Local Group. We have obtained deep (r=26.5) wide-field
g,r photometry of individual stars with the LBT under sub-arcsec seeing
conditions. The Color-Magnitude Diagram suggests that the stellar content of
the galaxy is dominated by an old, metal-poor population, with a significant
metallicity spread. A very clean detection of the RGB tip allows us to derive
an accurate distance of D=1.3 +/- 0.1 Mpc. Combining surface photometry with
star counts, we are able to trace the surface brightness profile of VV124 out
to ~ 5' = 1.9 kpc radius (where mu_r=30 mag/arcsec^2), showing that it is much
more extended than previously believed. Moreover, the surface density map
reveals the presence of two symmetric flattened wings emanating from the
central elongated spheroid and aligned with its major axis, resembling a
stellar disk seen nearly edge-on. We also present HI observations obtained with
the WSRT, the first ever of this object. A total amount of 10^6 M_sun of HI gas
is detected in VV124. Compared to the total luminosity, this gives a value of
M_HI/L_V=0.11, which is particularly low for isolated Local Group dwarfs. The
spatial distribution of the gas does not correlate with the observed stellar
wings. The systemic velocity of the HI in the region superposed to the stellar
main body of the galaxy is V_h=-25 km/s. The velocity field shows substructures
typical of galaxies of this size but no sign of rotation. The HI spectra
indicates the presence of a two-phase interstellar medium, again typical of
many dwarf galaxies. | A New Galaxy Cluster Merger Capable of Probing Dark Matter: Abell 56: We report the discovery of a binary galaxy cluster merger via a search of the
redMaPPer optical cluster catalog, with a projected separation of 535 kpc
between the BCGs. Archival XMM-Newton spectro-imaging reveals a gas peak
between the BCGs, suggesting a recent pericenter passage. We conduct a galaxy
redshift survey to quantify the line-of-sight velocity difference ($153\pm281$
km/s) between the two subclusters. We present weak lensing mass maps from
archival HST/ACS imaging, revealing masses of $M_{200}=4.5\pm0.8\times10^{14}$
and $2.8\pm0.7\times10^{14}$ M$_\odot$ associated with the southern and
northern galaxy subclusters respectively. We also present deep GMRT 650 MHz
data revealing extended emission, 420 kpc long, which may be an AGN tail but is
potentially also a candidate radio relic. We draw from cosmological n-body
simulations to find analog systems, which imply that this system is observed
fairly soon (60-271 Myr) after pericenter, and that the subcluster separation
vector is within 22$^\circ$ of the plane of the sky, making it suitable for an
estimate of the dark matter scattering cross section. We find $\sigma_{\rm
DM}=1.1\pm0.6$ cm$^2$/g, suggesting that further study of this system could
support interestingly tight constraints. |
Planck Data and Ultralight Axions: We examine the effects of photon-axion mixing on the CMB. We show that if
there are very underdense regions between us and the last scattering surface
which contain coherent magnetic fields (whose strength can be orders of
magnitude weaker than the current bounds), then photon-axion mixing can induce
observable deviations in the CMB spectrum. Specifically, we show that the
mixing can give rise to non-thermal spots on the CMB sky. As an example we
consider the well known CMB cold spot, which according to the Planck data has a
weak distortion from a black body spectrum, that can be fit by our model. While
this explanation of the non-thermality in the region of the cold spot is quite
intriguing, photon-axion oscillation do not explain the temperature of the cold
spot itself. Nevertheless we demonstrate the possible sensitivity of the CMB to
ultralight axions which could be exploited by observers. | Far-UV Fe Emission as Proxy of Eddington Ratios: The Eddington ratio is a key parameter that governs the diversity of quasar
properties. It can be scaled with a strong anti-correlation between optical Fe
II and [O III] emission. In search of such indicators in the far-UV band, the
HST far-UV spectra of 150 low-redshift quasars are analyzed in combination with
their optical SDSS counterparts. The strength of Fe II+Fe III 1123 emission is
significantly correlated with that of optical Fe II. A moderate correlation may
also exist between Fe II 1071 and optical Fe II. The finding opens the
possibility that far-UV Fe II emission may serve as a new gauge of the
Eddington ratios. The high- and low-ionization lines in the far-UV band display
different patterns: for the quasars with higher Eddington ratios, the
low-ionization UV lines are stronger, and the high-ionization lines are broader
and weaker. |
Low-energy modified gravity signatures on the large-scale structures: A large number of dark energy and modified gravity models lead to the same
expansion history of the Universe, hence, making it difficult to distinguish
them from observations. To make the calculations transparent, we consider
$f(R)$ gravity with a pressureless matter without making any assumption about
the form of $f(R)$. Using the late-time expansion history realizations
constructed by Shafieloo et al~\cite{2018-Shafieloo.etal-PRD}, we explicitly
show for any $f(R)$ model that the Bardeen potentials $\Psi$ and $\Phi$ evolve
differently. For an arbitrary $f(R)$ model that leads to late-time accelerated
expansion, we explicitly show that $|\Psi + \Phi|$ and its time-derivative
evolves differently than the $\Lambda$CDM model at lower redshifts. We show
that the $\Psi/\Phi$ has a significant deviation from unity for larger
wave-numbers. We discuss the implications of the results for the cosmological
observations. | Integral Field Spectroscopy of HII region complexes. The outer disk of
NGC 6946: Integral Field Spectroscopy obtained with PPak and the 3.5m telescope at the
Calar Alto Observatory has been used to study an outer HII region complex in
the well studied galaxy NGC 6946. This technique provides detailed maps of the
region in different emission lines yielding spatially resolved information
about the physical properties of the gas. The configuration was chosen to cover
the whole spectrum from 3600 up to 10000 A. We selected four luminous knots, to
perform a detailed integrated spectroscopic analysis of these structures and of
the whole PPak field-of-view (FOV). For all the knots the electron density has
been found to be very similar and below 100 cm^-3. The [OIII] electron
temperature was measured in knots A, B, C and in the integrated PPak-field, and
was found to be around 8000 K. The temperatures of [OII] and [SIII] were
estimated in the four cases. The elemental abundances computed from the "direct
method" are typical of high metallicity disk HII regions, with a mean value of
12+log(O/H)= 8.65, comparable to what has been found in this galaxy by other
authors for regions at similar galactocentric distance. Therefore, a remarkable
abundance uniformity is found despite the different excitations found
throughout the nebula. Wolf-Rayet features have been detected in three of the
knots, leading to a derived total number of WR stars of 125, 22 and 5, for
knots A, C and B, respectively. The integrated spectrum of the whole PPak FOV
shows high excitation and a relatively evolved age which does not correspond to
the individual knot evolutionary stages. Some effects associated to the loss of
spatial resolution could also be evidenced by the higher ionising temperature
that is deduced from the eta' parameter measured in the integrated PPak
spectrum with respect to that of the individual knots. |
Low-frequency integrated radio spectra of diffuse, steep-spectrum
sources in galaxy clusters: palaeontology with the MWA and ASKAP: Galaxy clusters have been found to host a range of diffuse, non-thermal
emission components, generally with steep, power law spectra. In this work we
report on the detection and follow-up of radio halos, relics, remnant radio
galaxies, and other fossil radio plasmas in Southern Sky galaxy clusters using
the Murchison Widefield Array and the Australian Square Kilometre Array
Pathfinder. We make use of the frequency coverage between the two radio
interferometers - from 88 to $\sim 900$ MHz - to characterise the integrated
spectra of these sources within this frequency range. Highlights from the
sample include the detection of a double relic system in Abell 3186, a
mini-halo in RXC J0137.2-0912, a candidate halo and relic in Abell 3399, and a
complex multi-episodic head-tail radio galaxy in Abell 3164. We compare this
selection of sources and candidates to the literature sample, finding sources
consistent with established radio power-cluster mass scaling relations.
Finally, we use the low-frequency integrated spectral index, $\alpha$ ($S_\nu
\propto \nu^\alpha$), of the detected sample of cluster remnants and fossil
sources to compare with samples of known halos, relics, remnants and fossils to
investigate a possible link between their electron populations. We find the
distributions of $\alpha$ to be consistent with relic and halo emission
generated by seed electrons that originated in fossil or remnant sources.
However, the present sample sizes are insufficient to rule out other scenarios. | Eppur è piatto? The cosmic chronometer take on spatial curvature and
cosmic concordance: The question of whether Cosmic Microwave Background (CMB) temperature and
polarization data from Planck favor a spatially closed Universe with curvature
parameter $\Omega_K<0$ has been the subject of recent intense discussions.
Attempts to break the geometrical degeneracy combining Planck data with
external datasets such as Baryon Acoustic Oscillation (BAO) measurements all
point towards a spatially flat Universe, at the cost of significant tensions
with Planck, which make the resulting dataset combination problematic. Settling
this issue requires identifying a dataset which can break the geometrical
degeneracy while not incurring in these tensions. We argue that cosmic
chronometers (CC), measurements of the expansion rate $H(z)$ from the relative
ages of massive early-type passively evolving galaxies, are the dataset we are
after. Furthermore, CC come with the additional advantage of being virtually
free of cosmological model assumptions. Combining Planck 2018 CMB temperature
and polarization data with the latest CC measurements, we break the geometrical
degeneracy and find $\Omega_K=-0.0054 \pm 0.0055$, consistent with a spatially
flat Universe and competitive with the Planck+BAO constraint. Our results are
stable against minimal parameter space extensions and CC systematics, and we
find no substantial tension between Planck and CC data within a non-flat
Universe, making the resulting combination reliable. Our results allow us to
assert with confidence that the Universe is spatially flat to the ${\cal
O}(10^{-2})$ level, a finding which might possibly settle the ongoing spatial
curvature debate, and lends even more support to the already very successful
inflationary paradigm. |
Mapping the Extended HI Distribution of Three Dwarf Galaxies: We present large field HI-line emission maps obtained with the single-dish
Green Bank Telescope centered on the dwarf irregular galaxies Sextans A, NGC
2366, and WLM. We do not detect the extended skirts of emission associated with
the galaxies that were reported from Effelsberg observations (Huchtmeier et al.
1981). The ratio of HI at 10^19 atoms cm^-2 to optical extents of these
galaxies are instead 2--3, which is normal for this type of galaxy. There is no
evidence for a truncation in the HI distribution >/=10^19 atoms cm^-2. | Multi-frequency angular power spectrum of the 21~cm signal from the
Epoch of Reionisation using the Murchison Widefield Array: The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to
spherically-averaged power spectra, and computes local fluctuations in the
angular power spectrum without need for line-of-sight spectral transform. To
test different approaches to MAPS and treatment of the foreground
contamination, and compare with the spherically-averaged power spectrum, and
the single-frequency angular power spectrum. We apply the MAPS to 110~hours of
data in $z=6.2-7.5$ obtained for the Murchison Widefield Array Epoch of
Reionisation experiment to compute the statistical power of 21~cm brightness
temperature fluctuations. In the presence of bright foregrounds, a filter is
applied to remove large-scale modes prior to MAPS application, significantly
reducing MAPS power due to systematics. The MAPS shows a contrast of
10$^2$--10$^3$ to a simulated 21~cm cosmological signal for spectral
separations of 0--4~MHz after application of the filter, reflecting results for
the spherically-averaged power spectrum. The single-frequency angular power
spectrum is also computed. At $z=7.5$ and $l=200$, we find an angular power of
53~mK$^2$, exceeding a simulated cosmological signal power by a factor of one
thousand. Residual spectral structure, inherent to the calibrated data, and not
spectral leakage from large-scale modes, is the dominant source of systematic
power bias. The single-frequency angular power spectrum yields slightly poorer
results compared with the spherically-averaged power spectrum, having applied a
spectral filter to reduce foregrounds. Exploration of other filters may improve
this result, along with consideration of wider bandwidths. |
Galaxy And Mass Assembly: Stellar Mass Estimates: This paper describes the first catalogue of photometrically-derived stellar
mass estimates for intermediate-redshift (z < 0.65) galaxies in the Galaxy And
Mass Assembly (GAMA) spectroscopic redshift survey. These masses, as well as
the full set of ancillary stellar population parameters, will be made public as
part of GAMA data release 2. Although the GAMA database does include NIR
photometry, we show that the quality of our stellar population synthesis fits
is significantly poorer when these NIR data are included. Further, for a large
fraction of galaxies, the stellar population parameters inferred from the
optical-plus-NIR photometry are formally inconsistent with those inferred from
the optical data alone. This may indicate problems in our stellar population
library, or NIR data issues, or both; these issues will be addressed for future
versions of the catalogue. For now, we have chosen to base our stellar mass
estimates on optical photometry only. In light of our decision to ignore the
available NIR data, we examine how well stellar mass can be constrained based
on optical data alone. We use generic properties of stellar population
synthesis models to demonstrate that restframe colour alone is in principle a
very good estimator of stellar mass-to-light ratio, M*/Li. Further, we use the
observed relation between restframe (g-i) and M*/Li for real GAMA galaxies to
argue that, modulo uncertainties in the stellar evolution models themselves,
(g-i) colour can in practice be used to estimate M*/Li to an accuracy of < ~0.1
dex. This 'empirically calibrated' (g-i)-M*/Li relation offers a simple and
transparent means for estimating galaxies' stellar masses based on minimal
data, and so provides a solid basis for other surveys to compare their results
to z < ~0.4 measurements from GAMA. | The Logotropic Dark Fluid as a unification of dark matter and dark
energy: We propose a heuristic unification of dark matter and dark energy in terms of
a single dark fluid with a logotropic equation of state $P=A\ln(\rho/\rho_P)$,
where $\rho$ is the rest-mass density, $\rho_P$ is the Planck density, and $A$
is the logotropic temperature. The energy density $\epsilon$ is the sum of a
rest-mass energy term $\rho c^2$ mimicking dark matter and an internal energy
term $u(\rho)=-P(\rho)-A$ mimicking dark energy. The logotropic temperature is
approximately given by $A \simeq
\rho_{\Lambda}c^2/\ln(\rho_P/\rho_{\Lambda})\simeq\rho_{\Lambda}c^2/[123
\ln(10)]$, where $\rho_{\Lambda}$ is the cosmological density. More precisely,
we obtain $A=2.13\times 10^{-9} \, {\rm g}\, {\rm m}^{-1}\, {\rm s}^{-2}$ that
we interpret as a fundamental constant. At the cosmological scale, this model
fullfills the same observational constraints as the $\Lambda$CDM model.
However, it has a nonzero velocity of sound and a nonzero Jeans length which,
at the beginning of the matter era, is about $\lambda_J=40.4\, {\rm pc}$, in
agreement with the minimum size of the dark matter halos observed in the
universe. At the galactic scale, the logotropic pressure balances gravitational
attraction and solves the cusp problem and the missing satellite problem. The
logotropic equation of state generates a universal rotation curve that agrees
with the empirical Burkert profile of dark matter halos up to the halo radius.
In addition, it implies that all the dark matter halos have the same surface
density $\Sigma_0=\rho_0 r_h=141\, M_{\odot}/{\rm pc}^2$ and that the mass of
dwarf galaxies enclosed within a sphere of fixed radius $r_{u}=300\, {\rm pc}$
has the same value $M_{300}=1.93\times 10^{7}\, M_{\odot}$, in remarkable
agreement with the observations. |
Spatially Resolved Chemistry in Nearby Galaxies II. The Nuclear Bar in
Maffei 2: We present 2" - 10" imaging of eleven transitions from nine molecular species
across the nuclear bar in Maffei 2. The data were obtained with the BIMA and
OVRO interferometers. The ten detected transitions are compared with existing
CO isotopologues, HCN, CS and millimeter continuum data. Dramatic spatial
variations among the mapped species are observed across the nuclear bar. A
principle component analysis is performed to characterize correlations between
the transitions, star formation and molecular column density. The analysis
reveals that HCN, HNC, HCO+ and 3 mm continuum are tightly correlated,
indicating a direct connection to massive star formation. We find two main
morphologically distinct chemical groups, CH3OH, SiO and HNCO comprising the
grain chemistry molecules, versus HCN, HNC, HCO+ and C2H, molecules strong in
the presence of star formation. The grain chemistry molecules, HNCO, CH3OH and
SiO, trace hydrodynamical bar shocks. The near constancy of the HNCO/CH3OH,
SiO/CH3OH and SiO/HNCO ratios argue that shock properties are uniform across
the nucleus. HCN/HCO+, HCN/HNC, HCN/CS and HCN/CO ratios are explained
primarily by variations in density. High HCO+/N2H+ ratios are correlated with
the C2H line, suggesting that this ratio may be a powerful new dense
photon-dominated region (PDR) probe in external galaxies. C2H reveals a
molecular outflow along the minor axis. The morphology and kinematics of the
outflow are consistent with an outflow age of 6-7 Myrs. | Ruling out the light WIMP explanation of the galactic 511 keV line: Over the past few decades, an anomalous 511 keV gamma-ray line has been
observed from the centre of the Milky Way. Dark matter (DM) in the form of
light weakly interacting massive particles (WIMPs) annihilating into
electron-positron pairs has been one of the leading hypotheses of the observed
emission. Given the small required cross section, a further coupling to lighter
particles is required to produce the correct relic density. Here, we derive
constraints from the Planck satellite on light WIMPs that were in equilibrium
with either the neutrino or electron sector in the early universe. For the
neutrino sector, we obtain a lower bound on the WIMP mass of 4 MeV for a real
scalar and 10 MeV for a Dirac fermion DM particle, at 95% CL. For the electron
sector, we find even stronger bounds of 7 and 11 MeV, respectively. Using these
results, we show that, in the absence of additional ingredients such as dark
radiation, the light thermally produced WIMP explanation of the 511 keV excess
is strongly disfavoured by the latest cosmological data. This suggests an
unknown astrophysical or more exotic DM source of the signal. |
Constraining the reionization and thermal history of the Universe using
a semi-numerical photon-conserving code SCRIPT: Given that the reionization history of cosmic hydrogen is yet to be
stringently constrained, it is worth checking the prospects of doing so using
physically motivated models and available observational data. For this purpose,
we use an extended version of the explicitly photon-conserving semi-numerical
model of reionization, $\texttt{SCRIPT}$, which also includes thermal evolution
of the intergalactic medium (IGM). The model incorporates the effects of
inhomogeneous recombination and radiative feedback self-consistently and is
characterized by five free parameters (two for the redshift-dependent
ionization efficiency, two for the ionizing escape fraction, and another for
reionization temperature increment). We constrain these free parameters by
simultaneously matching with various observational probes, e.g., estimates of
the ionized hydrogen fraction, the CMB scattering optical depth and the galaxy
UV luminosity function. In addition, we include the low-density IGM temperature
measurements obtained from Lyman-$\alpha$ absorption spectra at $z \sim 5.5$, a
probe not commonly used for Bayesian analysis of reionization parameters. We
find that the interplay of the various data sets, particularly inclusion of the
temperature data, leads to tightening of the parameter constraints. Our default
models prefer a late end of reionization (at $z \lesssim 6$), in agreement with
other recent studies. We can also derive constraints on the duration of
reionization, $\Delta z=1.81^{+0.51}_{-0.67}$ and the midpoint of reionization,
$z_{\mathrm{mid}}=7.0^{+0.30}_{-0.40}$. The constraints can be further
tightened by including other available and upcoming data sets. | The value of H_0 in the inhomogeneous Universe: Local measurements of the Hubble expansion rate are affected by structures
like galaxy clusters or voids. Here we present a fully relativistic treatment
of this effect, studying how clustering modifies the mean distance
(modulus)-redshift relation and its dispersion in a standard $\Lambda$CDM
universe. The best estimates of the local expansion rate stem from supernova
observations at small redshifts (0.01<z<0.1). It is interesting to compare
these local measurements with global fits to data from cosmic microwave
background anisotropies. In particular, we argue that cosmic variance (i.e. the
effects of the local structure) is of the same order of magnitude as the
current observational errors and must be taken into account in local
measurements of the Hubble expansion rate. |
The AMIGA sample of isolated galaxies: VIII. The rate of asymmetric HI
profiles in spiral galaxies: (abridged) Measures of the HI properties of a galaxy are among the most
sensitive interaction diagnostic at our disposal. We report here on a study of
HI profile asymmetries (e.g., lopsidedness) in a sample of some of the most
isolated galaxies in the local Universe. This presents us with an excellent
opportunity to quantify the range of intrinsic HI asymmetries and provides us
with a zero-point calibration for evaluating these measurements in less
isolated samples. We characterize the HI profile asymmetries and search for
correlations between HI asymmetry and their environments, as well as their
optical and far infrared (FIR) properties. We use high signal-to-noise global
HI profiles for galaxies in the AMIGA project (http://amiga.iaa.csic.es). We
restrict our study to N=166 galaxies with accurate measures of the HI shape
properties. We quantify asymmetries using a flux ratio parameter. The asymmetry
parameter distribution of our isolated sample is well described by a Gaussian
model. The width of the distribution is sigma=0.13, and could be even smaller
(sigma=0.11) if instrumental errors are reduced. Only 2% of our carefully
vetted isolated galaxies sample show an asymmetry in excess of 3sigma. By using
this sample we minimize environmental effects as confirmed by the lack of
correlation between HI asymmetry and tidal force (one-on-one interactions) and
neighbor galaxy number density. On the other hand, field galaxy samples show
wider distributions and deviate from a Gaussian curve. As a result we find
higher asymmetry rates (~10-20%) in such samples. We find evidence that the
spiral arm strength is inversely correlated with the HI asymmetry. We also find
an excess of FIR luminous galaxies with larger HI asymmetries that may be
spirals associated with hidden accretion events. Our sample presents the
smallest fraction of asymmetric HI profiles compared with any other yet
studied. | Probing quasar lifetimes with proximate $21$-centimetre absorption in
the diffuse intergalactic medium at redshifts $z\geq 6$: Enhanced ionizing radiation in close proximity to redshift $z\gtrsim 6$
quasars creates short windows of intergalactic Ly$\alpha$ transmission blueward
of the quasar Ly$\alpha$ emission lines. The majority of these Ly$\alpha$
near-zones are consistent with quasars that have optically/UV bright lifetimes
of $t_{\rm Q}\sim 10^{5}-10^{7}\rm\,yr$. However, lifetimes as short as $t_{\rm
Q}\lesssim 10^{4}\rm\,yr$ appear to be required by the smallest Ly$\alpha$
near-zones. These short lifetimes present an apparent challenge for the growth
of $\sim 10^{9}\rm\,M_{\odot}$ black holes at $z\gtrsim 6$. Accretion over
longer timescales is only possible if black holes grow primarily in an obscured
phase, or if the quasars are variable on timescales comparable to the
equilibriation time for ionized hydrogen. Distinguishing between very young
quasars and older quasars that have experienced episodic accretion with
Ly$\alpha$ absorption alone is challenging, however. We therefore predict the
signature of proximate 21-cm absorption around $z\gtrsim 6$ radio-loud quasars.
For modest pre-heating of intergalactic hydrogen by the X-ray background, where
the spin temperature $T_{\rm S} \lesssim 10^{2}\rm\,K$ prior to any quasar
heating, we find proximate 21-cm absorption should be observable in the spectra
of radio-loud quasars. The extent of the proximate 21-cm absorption is
sensitive to the integrated lifetime of the quasar. Evidence for proximate
21-cm absorption from the diffuse intergalactic medium within $2-3\rm\,pMpc$ of
a (radio-loud) quasar would be consistent with a short quasar lifetime, $t_{\rm
Q}\lesssim 10^{5}\rm\,yr$, and would provide a complementary constraint on
models for high redshift black hole growth. |
Planck 2013 results. XXIX. The Planck catalogue of Sunyaev-Zeldovich
sources: Addendum: We update the all-sky Planck catalogue of 1227 clusters and cluster
candidates (PSZ1) published in March 2013, derived from Sunyaev-Zeldovich (SZ)
effect detections using the first 15.5 months of Planck satellite observations.
Addendum. We deliver an updated version of the PSZ1 catalogue, reporting the
further confirmation of 86 Planck-discovered clusters. In total, the PSZ1 now
contains 947 confirmed clusters, of which 214 were confirmed as newly
discovered clusters through follow-up observations undertaken by the Planck
Collaboration. The updated PSZ1 contains redshifts for 913 systems, of which
736 (~80.6%) are spectroscopic, and associated mass estimates derived from the
Y_z mass proxy. We also provide a new SZ quality flag, derived from a novel
artificial neural network classification of the SZ signal, for the remaining
280 candidates. Based on this assessment, the purity of the updated PSZ1
catalogue is estimated to be 94%. In this release, we provide the full updated
catalogue and an additional readme file with further information on the Planck
SZ detections. | Exploring the role of the halo mass function for inferring astrophysical
parameters during reionisation: The detection of the 21-cm signal at $z\gtrsim6$ will reveal insights into
the properties of the first galaxies responsible for driving reionisation. To
extract this information, we perform parameter inference which requires
embedding 3D simulations of the 21-cm signal within a Bayesian inference
pipeline. Presently, when performing inference we must choose which sources of
uncertainty to sample and which to hold fixed. Since the astrophysics of
galaxies are much more uncertain than those of the underlying halo-mass
function (HMF), we usually parameterise and model the former while fixing the
latter. However, in doing so we may bias our inference of the properties of
these first galaxies. In this work, we explore the consequences of assuming an
incorrect choice of HMF and quantify the relative biases in our inferred
astrophysical model parameters when considering the wrong HMF. We then relax
this assumption by constructing a generalised five parameter model for the HMF
and simultaneously recover these parameters along with our underlying
astrophysical model. For this analysis, we use 21cmFAST and perform
Simulation-Based Inference by applying marginal neural ratio estimation to
learn the likelihood-to-evidence ratio using Swyft. Using a mock 1000 hour
observation of the 21-cm power spectrum from the forthcoming Square Kilometre
Array, conservatively assuming foreground wedge avoidance, we find assuming the
incorrect HMF can bias the recovered astrophysical parameters by up to
$\sim3-4\sigma$ even when including independent information from observed
luminosity functions. When considering our generalised HMF model, we recover
constraints on our astrophysical parameters with a factor of $\sim2-4$ larger
marginalised uncertainties. Importantly, these constraints are unbiased,
agnostic to the underlying HMF and therefore more conservative. |
Potential scientific synergies in weak lensing studies between the CSST
and Euclid space probes: Aims. With the next generation of large surveys coming to the stage of
observational cosmology soon, it is important to explore their potential
synergies and to maximise their scientific outcomes. In this study, we aim to
investigate the complementarity of the two upcoming space missions Euclid and
the China Space Station Telescope (CSST), focusing on weak lensing (WL)
cosmology. In particular, we analyse the photometric redshifts (photo-zs) and
the galaxy blending effects. For Euclid, WL measurements suffer from chromatic
PSF effects. For this, CSST can provide valuable information for Euclid to
obtain more accurate PSF, and to calibrate the color and color-gradient biases
for WL measurements.
Methods. We create image simulations for different surveys, and quantify the
photo-z performance. For blending analyses, we employ high-resolution
HST/CANDELS data to mock Euclid, CSST, and an LSST-like survey. We analyse the
blending fraction for different cases, and the blending effects on galaxy
photometry. Furthermore, we demonstrate that CSST can provide a large enough
number of high SNR multi-band galaxy images to calibrate the color-gradient
biases for Euclid.
Results. The sky coverage of Euclid lies entirely within the CSST footprint.
The combination of Euclid with CSST data can be done more uniformly than with
the various ground-based data. Our studies show that by combining Euclid and
CSST, we can reach a photo-z precision of $\sigma_{\rm NMAD} \approx 0.04$, and
an outlier fraction of $\eta\approx 2.4\%$. Because of the similarly high
resolutions, the data combination of Euclid and CSST can be relatively
straightforward for photometry. To include ground-based data, however,
sophisticated deblending utilizing priors from high-resolution space data is
demanded. The color-gradient biases for Euclid can be well calibrated to the
level of 0.1% using galaxies from CSST deep survey. | Isotropy theorem for cosmological Yang-Mills theories: We consider homogeneous non-abelian vector fields with general potential
terms in an expanding universe. We find a mechanical analogy with a system of N
interacting particles (with N the dimension of the gauge group) moving in three
dimensions under the action of a central potential. In the case of bounded and
rapid evolution compared to the rate of expansion, we show by making use of a
generalization of the virial theorem that for arbitrary potential and
polarization pattern, the average energy-momentum tensor is always diagonal and
isotropic despite the intrinsic anisotropic evolution of the vector field. We
consider also the case in which a gauge-fixing term is introduced in the action
and show that the average equation of state does not depend on such a term.
Finally, we extend the results to arbitrary background geometries and show that
the average energy-momentum tensor of a rapidly evolving Yang-Mills fields is
always isotropic and has the perfect fluid form for any locally inertial
observer. |
Environmental Dependence of Local Luminous Infrared Galaxies: We study the environmental dependence of local luminous infrared galaxies
(LIRGs) and ultraluminous infrared galaxies (ULIRGs) found in the Sloan Digital
Sky Survey (SDSS) data. The LIRG and ULIRG samples are constructed by
cross-correlating spectroscopic catalogs of galaxies of the SDSS Data Release 7
and the Infrared Astronomical Satellite Faint Source Catalog. We examine the
effects of the large-scale background density (Sigma_5), galaxy clusters, and
the nearest neighbor galaxy on the properties of infrared galaxies (IRGs). We
find that the fraction of LIRGs plus ULIRGs among IRGs (f_(U)LIRGs) and the
infrared luminosity (L_IR) of IRGs strongly depend on the morphology of and the
distance to the nearest neighbor galaxy: the probability for an IRG to be a
(U)LIRG (f_(U)LIRGs) and its L_IR both increase as it approaches a late-type
galaxy, but decrease as it approaches an early-type galaxy (within half the
virial radius of its neighbor). We find no dependence of f_(U)LIRGs on the
background density (surface galaxy number density) at fixed stellar mass of
galaxies. The dependence of f_(U)LIRGs on the distance to galaxy clusters is
also found to be very weak, but in highest-density regions such as the center
of galaxy clusters, few (U)LIRGs are found. These environmental dependence of
LIRGs and ULIRGs and the evolution of star formation rate (SFR)-environment
relation from high redshifts to low redshifts seem to support the idea that
galaxy-galaxy interactions/merging play a critical role in triggering the star
formation activity of LIRGs and ULIRGs. | On Weak Lensing Response Functions: We introduce the response function (RFs) approach to model the weak lensing
statistics in the context of separate universe formalism. Numerical results for
the RFs are presented for various semi-analytical models that include
perturbative modelling and variants of halo models. These results extend the
recent studies of the Integrated Bispectrum (IB) and Trispectrum to arbitrary
order. We find that due to the line-of-sight (los) projection effects, the
expressions for RFs are not identical to the squeezed correlation functions of
the same order. We compute the RFs in three-dimensions (3D) using the spherical
Fourier-Bessel (sFB) formalism which provides a natural framework for
incorporating photometric redshifts, and relate these expressions to
tomographic and projected statistics. We generalise the concept of $k$-cut
power spectrum to $k$-cut response functions. In addition to the response
function for high-order spectra, we also define their counterparts in real
space, since they are easier to estimate from surveys with low sky-coverage and
non-trivial survey boundaries. |
Searching for AGN Outflows: Spatially Resolved Chandra HETG Spectroscopy
of the NLR Ionization Cone in NGC 1068: We present initial results from a new 440-ks Chandra HETG GTO observation of
the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together
with Chandra's superb spatial and spectral resolution, allow an unprecedented
view of its nucleus and circumnuclear NLR. We perform the first spatially
resolved high-resolution X-ray spectroscopy of the `ionization cone' in any
AGN, and use the sensitive line diagnostics offered by the HETG to measure the
ionization state, density, and temperature at discrete points along the ionized
NLR. We argue that the NLR takes the form of outflowing photoionized gas,
rather than gas that has been collisionally ionized by the small-scale radio
jet in NGC 1068. We investigate evidence for any velocity gradients in the
outflow, and describe our next steps in modeling the spatially resolved spectra
as a function of distance from the nucleus. | Thermal Instabilities and Shattering in the High-Redshift WHIM:
Convergence Criteria and Implications for Low-Metallicity Strong HI Absorbers: Using a novel suite of cosmological simulations zooming in on a Mpc-scale
intergalactic sheet or "pancake" at z~3-5, we conduct an in-depth study of the
thermal properties and HI content of the warm-hot intergalactic medium (WHIM)
at those redshifts. The simulations span nearly three orders of magnitude in
gas-cell mass, from ~(7.7x10^6-1.5x10^4)Msun, one of the highest resolution
simulations of such a large patch of the inter-galactic medium (IGM) to date.
At z~5, a strong accretion shock develops around the main pancake following a
collision between two smaller sheets. Gas in the post-shock region proceeds to
cool rapidly, triggering thermal instabilities and the formation of a
multiphase medium. We find neither the mass, nor the morphology, nor the
distribution of HI in the WHIM to be converged at our highest resolution.
Interestingly, the lack of convergence is more severe for the less dense, more
metal-poor, intra-pancake medium (IPM) in between filaments and far from any
star-forming galaxies. As the resolution increases, the IPM develops a
shattered structure, with ~kpc scale clouds containing most of the HI. From our
lowest to highest resolution, the covering fraction of metal-poor
(Z<10^{-3}Zsun) Lyman-limit systems (NHI>10^{17.2}/cm^2) in the IPM at z~4
increases from (3-15)%, while that of Damped Lyman-alpha Absorbers
(NHI>10^{20}/cm^2) with similar metallicity increases threefold, from
(0.2-0.6)%, with no sign of convergence. We find that a necessary condition for
the formation of a multiphase, shattered structure is resolving the cooling
length, lcool=cs*tcool, at T~10^5K. If this scale is unresolved, gas "piles up"
at these temperatures and cooling to lower temperatures becomes very
inefficient. We conclude that state-of-the-art cosmological simulations are
still unable to resolve the multi-phase structure of the low-density IGM, with
potentially far-reaching implications. |
The Formation of Spiral Galaxies: Adiabatic Compression with Young's
Algorithm and the Relation of Dark Matter Haloes to Their Primordial
Antecedents: We utilize Young's algorithm to model the adiabatic compression of the dark
matter haloes of galaxies in the THINGS survey to determine the relationship
between the halo fit to the rotation curve and the corresponding primordial
halo prior to compression. Young's algorithm conserves radial action and
angular momentum, resulting in less halo compression than more widely utilized
approximations. We find that estimates of the parameters of the NFW haloes fit
to the current dark matter distribution systematically overestimate the
concentration and underestimate the virial velocity of the corresponding
primordial halo. It is the latter that is predicted by dark matter simulations;
so accounting for compression is a necessary step for evaluating whether
massive galaxies are consistent with dark matter-only simulations. The inferred
primordial haloes broadly follow the c-V200 relation expected in a LCDM
cosmogony, but often scatter to lower concentrations. We are unable to obtain
fits at all for those galaxies whose current dark matter haloes are poorly
described by the NFW form. We thus find a mixed bag: some galaxies are
reasonably well described by adiabatic compression within a primordial NFW
halo, while others require additional mechanisms that reduce the density of
dark matter below the primordial initial condition. | Neutrino clustering in the Milky Way: The Cosmic Neutrino Background is a prediction of the standard cosmological
model, but it has been never observed directly. In the experiments with the aim
of detecting relic CNB neutrinos, currently under development, the expected
event rate depends on the local density of relic neutrinos. Since massive
neutrinos can be attracted by the gravitational potential of our galaxy and
cluster around it, a local overdensity of cosmic neutrinos should exist.
Considering the minimal masses guaranteed by neutrino oscillations, we review
the computation of the local density of relic neutrinos and we present
realistic prospects for a PTOLEMY-like experiment. |
The impact of ISM turbulence, clustered star formation and feedback on
galaxy mass assembly through cold flows and mergers: Two of the dominant channels for galaxy mass assembly are cold flows (cold
gas supplied via the filaments of the cosmic web) and mergers. How these
processes combine in a cosmological setting, at both low and high redshift, to
produce the whole zoo of galaxies we observe is largely unknown. Indeed there
is still much to understand about the detailed physics of each process in
isolation. While these formation channels have been studied using
hydrodynamical simulations, here we study their impact on gas properties and
star formation (SF) with some of the first simulations that capture the
multiphase, cloudy nature of the interstellar medium (ISM), by virtue of their
high spatial resolution (and corresponding low temperature threshold). In this
regime, we examine the competition between cold flows and a
supernovae(SNe)-driven outflow in a very high-redshift galaxy (z {\approx} 9)
and study the evolution of equal-mass galaxy mergers at low and high redshift,
focusing on the induced SF. We find that SNe-driven outflows cannot reduce the
cold accretion at z {\approx} 9 and that SF is actually enhanced due to the
ensuing metal enrichment. We demonstrate how several recent observational
results on galaxy populations (e.g. enhanced HCN/CO ratios in ULIRGs, a
separate Kennicutt Schmidt (KS) sequence for starbursts and the population of
compact early type galaxies (ETGs) at high redshift) can be explained with
mechanisms captured in galaxy merger simulations, provided that the multiphase
nature of the ISM is resolved. | Mid-Infrared Spectroscopy of Optically Faint Extragalactic 70 micron
Sources: We present mid-infrared spectra of sixteen optically faint sources with 70
micron fluxes in the range 19-38mJy. The sample spans a redshift range of
0.35<z<1.9, with most lying between 0.8<z<1.6, and has infrared luminosities of
10^{12} - 10^{13} solar luminosities. Ten of 16 objects show prominent
polycyclic aromatic hydrocarbon (PAH) emission features; four of 16 show weak
PAHs and strong silicate absorption, and two objects have no discernable
spectral features. Compared to samples with 24 micron fluxes >10mJy, the 70\um
sample has steeper IR continua and higher luminosities. The PAH dominated
sources are among the brightest starbursts seen at any redshift, and reside in
a redshift range where other selection methods turn up relatively few sources.
The absorbed sources are at higher redshifts and have higher luminosities than
the PAH dominated sources, and may show weaker luminosity evolution. We
conclude that a 70 micron selection extending to ~20mJy, in combination with
selections at mid-IR and far-IR wavelengths, is necessary to obtain a complete
picture of the evolution of IR-luminous galaxies over 0<z<2. |
Identifying frequency decorrelated dust residuals in B-mode maps by
exploiting the spectral capability of bolometric interferometry: Astrophysical polarized foregrounds represent the most critical challenge in
Cosmic Microwave Background (CMB) B-mode experiments. Multi-frequency
observations can be used to constrain astrophysical foregrounds to isolate the
CMB contribution. However, recent observations indicate that foreground
emission may be more complex than anticipated.
We investigate how the increased spectral resolution provided by band
splitting in Bolometric Interferometry (BI) through a technique called spectral
imaging can help control the foreground contamination in the case of
unaccounted Galactic dust frequency decorrelation along the line-of-sight.
We focus on the next generation ground-based CMB experiment CMB-S4, and
compare its anticipated sensitivities, frequency and sky coverage with a
hypothetical version of the same experiment based on BI. We perform a
Monte-Carlo analysis based on parametric component separation methods (FGBuster
and Commander) and compute the likelihood on the recovered tensor-to-scalar
ratio.
The main result of this analysis is that spectral imaging allows us to detect
systematic uncertainties on r from frequency decorrelation when this effect is
not accounted for in component separation. Conversely, an imager would detect a
biased value of r and would be unable to spot the presence of a systematic
effect. We find a similar result in the reconstruction of the dust spectral
index, where we show that with BI we can measure more precisely the dust
spectral index also when frequency decorrelation is present.
The in-band frequency resolution provided by BI allows us to identify dust
LOS frequency decorrelation residuals where an imager of similar performance
would fail. This opens the prospect to exploit this potential in the context of
future CMB polarization experiments that will be challenged by complex
foregrounds in their quest for B-modes detection. | Testing charge quantization with axion string-induced cosmic
birefringence: We demonstrate that the Peccei-Quinn-electromagnetic anomaly coefficient
$\mathcal A$ can be directly measured from axion string-induced cosmic
birefringence by applying scattering transform to the anisotropic polarization
rotation of the cosmic microwave background. This breaks the degeneracy between
$\mathcal A$ and the effective number of string loops in traditional inference
analyses that are solely based on the spatial power spectrum of polarization
rotation. Carrying out likelihood-based parameter inference on mock rotation
realizations generated according to phenomenological string network models, we
show that scattering transform is able to extract enough non-Gaussian
information to clearly distinguish a number of discrete $\mathcal A$ values,
for instance $\mathcal{A}=1/9,\,1/3,\,2/3$, in the ideal case of noise-free
rotation reconstruction, and, to a lesser but interesting degree, at
reconstruction noise levels comparable to that expected for the proposed CMB-HD
concept. In the event of a statistical detection of cosmic birefringence by
Stage III or IV CMB experiments, our technique can be applied to test the
stringy nature of the birefringence pattern and extract fundamental information
about the smallest unit of charge in theories beyond the Standard Model. |
Recoiled star clusters in the Milky Way halo: N-body simulations and a
candidate search through SDSS: During the formation of the Milky Way, > 100 central black holes (BHs) may
have been ejected from their small host galaxies as a result of asymmetric
gravitational wave emission. We previously showed that many of these BHs are
surrounded by a compact cluster of stars that remained bound to the BH during
the ejection process. In this paper, we perform long term N-body simulations of
these star clusters to determine the distribution of stars in these clusters
today. These numerical simulations, reconciled with our Fokker-Planck
simulations, show that stellar density profile follows a power-law with slope ~
-2.15, and show that large angle scattering and tidal disruptions remove 20 -
90% of the stars by ~10^10 yr. We then analyze the photometric and
spectroscopic properties of recoiled clusters accounting for the small number
of stars in the clusters. We use our results to perform a systematic search for
candidates in the Sloan Digital Sky Survey. We find no spectroscopic
candidates, in agreement with our expectations from the completeness of the
survey. Using generic photometric models of present day clusters we identify
~100 recoiling cluster candidates. Follow-up spectroscopy would be able to
determine the nature of these candidates. | Neutrinos in Non-linear Structure Formation - a Simple SPH Approach: We present a novel method for implementing massive neutrinos in N-body
simulations. Instead of sampling the neutrino velocity distribution by
individual point particles we take neutrino free-streaming into account by
treating it as an effective redshift dependent sound speed in a perfect
isothermal fluid, and assume a relation between the sound speed and velocity
dispersion of the neutrinos. Although the method fails to accurately model the
true neutrino power spectrum, it is able to calculate the total matter power
spectrum to the same accuracy as more complex hybrid neutrino methods, except
on very small scales. We also present an easy way to update the publicly
available Gadget-2 version with this neutrino approximation. |
{\em Herschel}-ATLAS/GAMA: The Environmental Density of Far-Infrared
Bright Galaxies at $z \leq 0.5$: We compare the environmental and star formation properties of far-infrared
detected and non--far-infrared detected galaxies out to $z \sim0.5$. Using
optical spectroscopy and photometry from the Galaxy And Mass Assembly (GAMA)
and Sloan Digital Sky Survey (SDSS), with far-infrared observations from the
{\em Herschel}-ATLAS Science Demonstration Phase (SDP), we apply the technique
of Voronoi Tessellations to analyse the environmental densities of individual
galaxies. Applying statistical analyses to colour, $r-$band magnitude and
redshift-matched samples, we show there to be a significant difference at the
3.5$\sigma$ level between the normalized environmental densities of these two
populations. This is such that infrared emission (a tracer of star formation
activity) favours underdense regions compared to those inhabited by exclusively
optically observed galaxies selected to be of the same $r-$band magnitude,
colour and redshift. Thus more highly star-forming galaxies are found to reside
in the most underdense environments, confirming previous studies that have
proposed such a correlation. However, the degeneracy between redshift and
far-infrared luminosity in our flux-density limited sample means that we are
unable to make a stronger statement in this respect. We then apply our method
to synthetic light cones generated from semi-analytic models, finding that over
the whole redshift distribution the same correlations between star-formation
rate and environmental density are found. | The radio-loud active nucleus in the "dark lens" galaxy J1218+2953: Context: There is a possibility that the optically unidentified radio source
J1218+2953 may act as a gravitational lens, producing an optical arc ~4" away
from the radio position. Until now, the nature of the lensing object has been
uncertain since it is not detected in any waveband other than the radio. The
estimated high mass-to-light ratio could even allow the total mass of this
galaxy to be primarily in the form of dark matter. In this case, J1218+2953
could be the first known example of a "dark lens".
Aims: We investigate the nature of J1218+2953 by means of high-resolution
radio imaging observations to determine whether there is a radio-loud active
galactic nucleus (AGN) in the position of the lensing object.
Methods: We report on Very Long Baseline Interferometry (VLBI) observations
with the European VLBI Network (EVN) at 1.6 and 5 GHz.
Results: Our images, having angular resolutions of ~1 to ~10 milli-arcseconds
(mas), reveal a rich and complex radio structure extending to almost 1". Based
on its radio spectrum and structure, J1218+2953 can be classified as a compact
steep-spectrum (CSS) source, and as a medium-size symmetric object (MSO). The
object harbours an AGN. It is also found as an X-ray source in the XMM-Newton
EPIC (European Photon Imaging Cameras) instrument serendipitous source
catalogue.
Conclusions: Rather than being a dark lens, J1218+2953 is most likely a
massive, heavily obscured galaxy in which the nuclear activity is currently in
an early evolutionary stage. |
Using quasar and gamma-ray burst measurements to constrain cosmological
dark energy models: Observational evidence for the accelerated expansion of the universe requires
dark energy for its explanation if general relativity is an accurate model of
gravity. However, dark energy is a mysterious quantity and we do not know much
about its nature so understanding dark energy is an exciting scientific
challenge. Cosmological dark energy models are fairly well tested in the low
and high redshift parts of the universe. The highest of the low redshift,
$z\sim2.3$, region is probed by baryon acoustic oscillation (BAO) measurements
and the only high redshift probe is the cosmic microwave background anisotropy
which probes the $z\sim1100$ part of redshift space. In the intermediate
redshift range $2.3 < z < 1100$ there are only a handful of observational
probes and cosmological models are poorly tested in this region.
In this thesis we constrain three pairs of general relativistic cosmological
dark energy models using observational data which reach beyond the current BAO
limit. We use quasar X-ray and UV flux measurements, the current version of
these data span $0.009 \leq z \leq 7.5413$. We have discovered that most of
these data cannot be standardized using the proposed method. However, the lower
redshift part, $z \lesssim 1.5-1.7$, of these data are standardizable and can
be used to derive lower-$z$ cosmological constraints. Another data set we use
are gamma-ray burst measurements which span $0.3399 \leq z \leq 8.2$.
Cosmological constraints derived from these data are significantly weaker than,
but consistent with, those obtained from better-established cosmological
probes. We also study and standardize 78 reverberation-measured Mg II time-lag
quasars in the redshift range $0.0033 \leq z \leq 1.89$ by using their
radius-luminosity relation. We also study 118 reverberation-measured H$\beta$
time-lag quasars which span $0.0023 \leq z \leq 0.89$. | High Redshift Radio Galaxies: Laboratories for Massive Galaxy and
Cluster Formation in the early Universe: High redshift radio galaxies are among the largest, most luminous, most
massive, and most beautiful objects in the Universe. They are generally
identified from their radio emission, thought to be powered by accretion of
matter onto supermassive black holes in the nuclei of their host galaxies.
Observations show that they are energetic sources of radiation throughout most
of the electromagnetic spectrum, including relativistic plasma, gas and dust,
stars and the active galactic nuclei (AGN). 1 HzRGs are inferred to be
extremely massive, including old stars (up to $\sim$ 10$^{12}$ M$_{\odot}$),
hot gas (up to $\sim$ 10$^{12}$ M$_{\odot}$) and molecular gas (up to $\sim$
10$^{11}$ M$_{\odot}$).Because they are highly luminous and (unlike quasars)
spatially resolvable from the ground, most components of HzRGs provide
important diagnostic information about the spatial distributions of processes
within HzRGs and their environment. The fact that the different constituents
are present in the same objects and that the {\bf {\it interrelationships and
interactions between them}} can be studied make distant radio galaxies unique
laboratories for probing massive galaxy and cluster formation in the early
Universe. |
The Foundation Supernova Survey: Measuring Cosmological Parameters with
Supernovae from a Single Telescope: Measurements of the dark energy equation-of-state parameter, $w$, have been
limited by uncertainty in the selection effects and photometric calibration of
$z<0.1$ Type Ia supernovae (SNe Ia). The Foundation Supernova Survey is
designed to lower these uncertainties by creating a new sample of $z<0.1$ SNe
Ia observed on the Pan-STARRS system. Here, we combine the Foundation sample
with SNe from the Pan-STARRS Medium Deep Survey and measure cosmological
parameters with 1,338 SNe from a single telescope and a single, well-calibrated
photometric system. For the first time, both the low-$z$ and high-$z$ data are
predominantly discovered by surveys that do not target pre-selected galaxies,
reducing selection bias uncertainties. The $z>0.1$ data include 875 SNe without
spectroscopic classifications and we show that we can robustly marginalize over
CC SN contamination. We measure Foundation Hubble residuals to be fainter than
the pre-existing low-$z$ Hubble residuals by $0.046 \pm 0.027$ mag (stat+sys).
By combining the SN Ia data with cosmic microwave background constraints, we
find $w=-0.938 \pm 0.053$, consistent with $\Lambda$CDM. With 463
spectroscopically classified SNe Ia alone, we measure $w=-0.933\pm0.061$. Using
the more homogeneous and better-characterized Foundation sample gives a 55%
reduction in the systematic uncertainty attributed to SN Ia sample selection
biases. Although use of just a single photometric system at low and high
redshift increases the impact of photometric calibration uncertainties in this
analysis, previous low-$z$ samples may have correlated calibration
uncertainties that were neglected in past studies. The full Foundation sample
will observe up to 800 SNe to anchor the LSST and WFIRST Hubble diagrams. | The Rising Star-Formation Histories of Distant Galaxies and Implications
for Gas Accretion with Time: Distant galaxies show correlations between their current star-formation rates
(SFRs) and stellar masses, implying that their star-formation histories (SFHs)
are highly similar. Moreover, observations show that the UV luminosities and
stellar masses grow from z=8 to 3, implying that the SFRs increase with time.
We compare the cosmologically averaged evolution in galaxies at 3 < z < 8 at
constant comoving number density, n = 2 x 10^-4 Mpc^-3. This allows us to study
the evolution of stellar mass and star formation in the galaxy predecessors and
descendants in ways not possible using galaxies selected at constant stellar
mass or SFR, quantities that evolve strongly in time. We show that the average
SFH of these galaxies increase smoothly from z=8 to 3 as SFR ~ t^alpha with
alpha = 1.7 +/- 0.2. This conflicts with assumptions that the SFR is either
constant or declines exponentially in time. We show that the stellar mass
growth in these galaxies is consistent with this derived SFH. This provides
evidence that the slope of the high-mass end of the IMF is approximately
Salpeter unless the duty cycle of star formation is much less than unity. We
argue that these relations follow from gas accretion (either through accretion
or delivered by mergers) coupled with galaxy disk growth under the assumption
that the SFR depends on the local gas surface density. This predicts that gas
fractions decrease from z=8 to 3 on average as f_gas ~ (1+z)^0.9 for galaxies
with this number density. The implied galaxy gas accretion rates at z > 4 are
as fast and may even exceed the SFR: this is the "gas accretion epoch". At z <
4 the SFR overtakes the implied gas accretion rate, indicating a period where
galaxies consume gas faster than it is acquired. At z < 3, galaxies with this
number density depart from these relations implying that star formation and gas
accretion are slowed at later times. |
Towards a panchromatic picture of galaxy evolution during the
reionization epoch: There are thousands of confirmed detections of star forming galaxies at high
redshift (z > 4). These observations rely primarily on the detection of the
spectral Lyman Break and the Lyman-alpha emission line. Theoretical modelling
of these sources helps to interpret the observations in the framework of the
standard cosmological paradigm. We present results from the High-z MareNostrum
Project, aimed at constructing a panchromatic picture of the high redshift
galaxy evolution that will improve our understanding of young star forming
galaxies. Our simulation successfully reproduces the observational constraints
from Lyman Break Galaxies and Lyman-alpha emitters at 5 < z < 7 . Based on this
model we make predictions on the expected Far Infrared (FIR) emission that
should be observed for LAEs. These predictions will help to settle down the
question on the dust content of massive high-z galaxies, an issue that will be
feasible to probe observationally with the Atacama Large Millimetre Array
(ALMA). | Spectroscopic Study of Globular Clusters in the Halo of M31 with
Xinglong 2.16m Telescope: We present the spectroscopic observations for 11 confirmed globular clusters
of M31 with the OMR spectrograph on 2.16m telescope at Xinglong site of
National Astronomical Observatories, Chinese Academy of Sciences. Nine of our
sample clusters are located in the halo of M31 and the most remote one is out
to a projected radius of 78.75 kpc from the galactic center. For all our sample
clusters, we measured the Lick absorption-line indices and the radial
velocities. It is noted that most GCs of our sample are distinct from the HI
rotation curve of M31 galaxy, especially for B514, MCGC5, H12 and B517,
suggesting that most of our sample clusters do not have kinematic association
with the star forming young disk of the galaxy. We fitted the absorption line
indices with the updated stellar population model Thomas et al. (2010) with two
different tracks of Cassisi and Padova, separately, by applying the
$\chi^2-$minimization method. The fitting results show that all our sample
clusters are older than 10 Gyr, and metal-poor ($-0.91 \le $ [Fe/H] $\le -2.38$
dex). After merging the spectroscopic metallicity of our work with the
previously published ones, we extended the cluster sample out to a projected
radius of 117 kpc from the galaxy's center. We found the metallicity gradient
for all the confirmed clusters exists with a slope of $-0.028\pm0.001$ dex
kpc$^{-1}$. However, the slope turns to be $-0.018\pm0.001$ dex kpc$^{-1}$ for
all the halo clusters, which is much shallower. If we only consider the outer
halo clusters with $r_{\rm p}>25$ kpc, the slope becomes $-0.010\pm0.002$ dex
kpc$^{-1}$ and if one cluster G001 is excluded from the outer halo sample, the
slope is $-0.004\pm0.002$ dex kpc$^{-1}$. Thus we conclude that metallicity
gradient for M31 outer halo clusters is not significant, which agrees well with
the previous findings. |
Dust Emission in Early-Type Galaxies with the Herschel Virgo Cluster
Survey: We have searched for dust in an optical sample of 910 Early-Type Galaxies
(ETG) in the Virgo cluster (447 of which are optically complete at m_pg <=
18.0), extending also to the dwarf ETG, using Herschel images at 100, 160, 250,
350 and 500 microns. Dust was found in 52 ETG (46 are in the optically complete
sample), including M87 and another 3 ETG with strong synchrotron emisssion.
Dust is detected in 17% of ellipticals, 41% of lenticulars, and in about 4% of
dwarf ETG. The dust-to-stars mass ratio increases with decreasing optical
luminosity, and for some dwarf ETG reaches values similar to those of the dusty
late-type galaxies. Slowly rotating ETG are more likely to contain dust than
fast rotating ones. Only 8 ETG have both dust and HI, while 39 have only dust
and 8 have only HI, surprisingly showing that only rarely dust and HI survive
together. ETG with dust appear to be concentrated in the densest regions of the
cluster, while those with HI tend to be at the periphery. ETG with an X-ray
active SMBH are more likely to have dust and vice versa the dusty ETG are more
likely to have an active SMBH. | The maximum mass of dark matter existing in compact stars based on the
self-interacting fermionic model: By assuming that only gravitation acts between dark matter (DM) and normal
matter (NM), we studied DM admixed neutron stars (DANSs) using the two-fluid
TOV equations. The NM and DM of compact stars are simulated by the relativistic
mean field (RMF) theory and non-self-annihilating self-interacting fermionic
model, respectively. The effects of the particle mass of fermionic DM $m_f$ and
the interaction strength parameter $y$ on the properties of DANSs are
investigated in detail. $m_f$ and $y$ are considered as the free parameters due
to the lack of information about the particle nature of DM so far. For a DANS,
we suggest a simple universal relationship $M_D^{\max}=(0.267 y
+0.627-3.21\frac{M_N}{\M_{\odot}})( \frac{1\GeV}{{m_f}})^2 \M_{\odot}$ for
$y>100$, where $M_D^{\max}$ is the maximum mass of DM existing in DANSs and
$M_N$ is the mass of the neutron star without DM. For free fermion DM model
($y$=0), the relationship becomes $
M_D^{\max}=(0.627-0.027\frac{M_N^2}{\M_{\odot}^2}) ( \frac{1\GeV}{{m_f}})^2
\M_{\odot}$. The radius of DM $R_D$ shows a linear relationship with
$M_D^{\max}$ in DANSs, namely $R_D=(7.02 \frac{M_D^{\max}}{
\M_{\odot}}+1.36)$~km. These conclusions are independent of the different NM
EOSs from RMF theory. Such a kind of universal relationship connecting the
nature of DM particle and mass of stars might shed light on the constraining
the nature of the DM by indirect method. |
Forecasting isocurvature models with CMB lensing information: axion and
curvaton scenarios: Some inflationary models predict the existence of isocurvature primordial
fluctuations, in addition to the well known adiabatic perturbation. Such mixed
models are not yet ruled out by available data sets. In this paper we explore
the possibility of obtaining better constraints on the isocurva- ture
contribution from future astronomical data. We consider the axion and curvaton
inflationary scenarios, and use Planck satellite experimental specifications
together with SDSS galaxy survey to forecast for the best parameter error
estimation by means of the Fisher information matrix formal- ism. In
particular, we consider how CMB lensing information can improve this forecast.
We found substantial improvements for all the considered cosmological
parameters. In the case of isocurvature amplitude this improvement is strongly
model dependent, varying between less than 1% and above 20% around its fiducial
value. Furthermore, CMB lensing enables the degeneracy break between the
isocurvature amplitude and correlation phase in one of the models. In this
sense, CMB lensing information will be crucial in the analysis of future data. | Dark matter powered stars: Constraints from the extragalactic background
light: The existence of predominantly cold non-baryonic dark matter is unambiguously
demonstrated by several observations (e.g., structure formation, big bang
nucleosynthesis, gravitational lensing, and rotational curves of spiral
galaxies). A candidate well motivated by particle physics is a weakly
interacting massive particle (WIMP). Self-annihilating WIMPs would affect the
stellar evolution especially in the early universe. Stars powered by
self-annihilating WIMP dark matter should possess different properties compared
with standard stars. While a direct detection of such dark matter powered stars
seems very challenging, their cumulative emission might leave an imprint in the
diffuse metagalactic radiation fields, in particular in the mid-infrared part
of the electromagnetic spectrum. In this work the possible contributions of
dark matter powered stars (dark stars; DSs) to the extragalactic background
light (EBL) are calculated. It is shown that existing data and limits of the
EBL intensity can already be used to rule out some DS parameter sets. |
Cosmic equation of state from combined angular diameter distances: Does
the tension with luminosity distances exist?: Using a relatively complete observational data concerning four angular
diameter distance (ADD) measurements and %synthetic combined SN+GRB
observations representing current luminosity distance (LD) data, this paper
investigates the %tension between compatibility of these two cosmological
distances considering three classes of dark energy equation of state (EoS)
reconstruction. In particular, we use strongly gravitationally lensed systems
from various large systematic gravitational lens surveys and galaxy clusters,
which yield the Hubble constant independent ratio between two angular diameter
distances $D_{ls}/D_s$ data. Our results demonstrate that, with more general
categories of standard ruler data, ADD and LD data are compatible at $1\sigma$
level. Secondly, we note that consistency between ADD and LD data %are blind is
maintained irrespective of the EoS parameterizations: there is a good match
between the universally explored CPL model and other formulations of cosmic
equation of state. Especially for the truncated GEoS model with $\beta=-2$, the
conclusions obtained with ADD and LD are almost the same. Finally, statistical
analysis of generalized dark energy equation of state performed on four classes
of ADD data provides stringent constraints on the EoS parameters $w_0$,
$w_{\beta}$ and $\beta$, which suggest that dark energy was a subdominant
component at early times. Moreover, the GEoS parametrization with $\beta\simeq
1$ seems to be a more favorable two-parameter model to characterize the cosmic
equation of state, because the combined angular diameter distance data
(SGL+CBF+BAO+WMAP9) provide the best-fit value $\beta=0.751^{+0.465}_{-0.480}$. | Substructure in the lens HE 0435-1223: We investigate the properties of dark matter substructure in the
gravitational lens HE 0435-1223 (z_l=0.455) via its effects on the positions
and flux ratios of the quadruply-imaged background quasar (z_s=1.689). We start
with a smooth mass model, add individual, truncated isothermal clumps near the
lensed images, and use the Bayesian evidence to compare the quality of
different models. Compared with smooth models, models with at least one clump
near image A are strongly favored. The mass of this clump within its Einstein
radius is log(Mein/Msun) = 7.65 +0.87/-0.84. The Bayesian evidence provides
weaker support for a second clump near image B, with log(Mein/Msun) = 6.55
+1.01/-1.51. We also examine models with a full population of substructure, and
find the mass fraction in substructure at the Einstein radius to be f_sub >
0.00077, assuming the total clump masses follow a mass function dN/dM
proportional to M^(-1.9) over the range M = 10^7-10^10 Msun. Few-clump and
population models produce similar Bayesian evidence values, so neither type of
model is objectively favored. |
Weak-lensing mass calibration of the Sunyaev-Zel'dovich effect using
APEX-SZ galaxy clusters: The use of galaxy clusters as precision cosmological probes relies on an
accurate determination of their masses. However, inferring the relationship
between cluster mass and observables from direct observations is difficult and
prone to sample selection biases. In this work, we use weak lensing as the best
possible proxy for cluster mass to calibrate the Sunyaev-Zel'dovich (SZ) effect
measurements from the APEX-SZ experiment. For a well-defined (ROSAT) X-ray
complete cluster sample, we calibrate the integrated Comptonization parameter,
$Y_{\rm SZ}$, to the weak-lensing derived total cluster mass, $M_{500}$. We
employ a novel Bayesian approach to account for the selection effects by
jointly fitting both the SZ Comptonization, $Y_{\rm SZ}\text{--}M_{500}$, and
the X-ray luminosity, $L_{\rm x}\text{--}M_{500}$, scaling relations. We also
account for a possible correlation between the intrinsic (log-normal) scatter
of $L_{\rm x}$ and $Y_{\rm SZ}$ at fixed mass. We find the corresponding
correlation coefficient to be $r= 0.47_{-0.35}^{+0.24}$, and at the current
precision level our constraints on the scaling relations are consistent with
previous works. For our APEX-SZ sample, we find that ignoring the covariance
between the SZ and X-ray observables biases the normalization of the $Y_{\rm
SZ}\text{--}M_{500}$ scaling high by $1\text{--}2\sigma$ and the slope low by
$\sim 1\sigma$, even when the SZ effect plays no role in the sample selection.
We conclude that for higher-precision data and larger cluster samples, as
anticipated from on-going and near-future cluster cosmology experiments,
similar biases (due to intrinsic covariances of cluster observables) in the
scaling relations will dominate the cosmological error budget if not accounted
for correctly. | Slow Galaxy Growth within Rapidly Growing Dark Matter Halos: In cold dark matter cosmologies, the most massive dark matter halos undergo
rapid growth between a redshift of z=1 and z=0, corresponding to the past 7
billion years of cosmic time. There is thus an expectation that the stellar
masses of the most massive galaxies will also rapidly grow via merging over
this redshift range. While there are examples of massive merging galaxies at
low redshift, recent observations show that the stellar masses of massive
galaxies have grown by only 30% since z=1. Some of the literature claims that
the slow growth of massive galaxies is contrary to the CDM paradigm, although
this is not necessarily the case. To determine why massive galaxies are not
growing rapidly, we have modeled how galaxies populate dark matter halos. To do
this, we have measured the space density and spatial clustering of redshift z<1
galaxies in the Bootes field of the NOAO Deep Wide-Field Survey. We have then
modeled the observations using the halo occupation distribution (HOD)
formalism. We find that the stellar masses of the largest galaxies are
proportional to dark matter halo mass to the power of a third. In the most
massive dark matter halos, we also find that the stellar mass is distributed
mostly among "satellite" galaxies. As a consequence, the stellar masses of
large galaxies are expected to increase relatively slowly, even though they
reside within rapidly growing dark matter halos. |
A statistical standard siren measurement of the Hubble constant from the
LIGO/Virgo gravitational wave compact object merger GW190814 and Dark Energy
Survey galaxies: We present a measurement of the Hubble constant $H_0$ using the gravitational
wave (GW) event GW190814, which resulted from the coalescence of a 23 $M_\odot$
black hole with a 2.6 $M_\odot$ compact object, as a standard siren. No
compelling electromagnetic counterpart has been identified for this event, thus
our analysis accounts for thousands of potential host galaxies within a
statistical framework. The redshift information is obtained from the
photometric redshift (photo-$z$) catalog from the Dark Energy Survey. The
luminosity distance is provided by the LIGO/Virgo gravitational wave sky map.
Since this GW event has the second-smallest localization volume after GW170817,
GW190814 is likely to provide the best constraint on cosmology from a single
standard siren without identifying an electromagnetic counterpart. Our analysis
uses photo-$z$ probability distribution functions and corrects for photo-$z$
biases. We also reanalyze the binary-black hole GW170814 within this updated
framework. We explore how our findings impact the $H_0$ constraints from
GW170817, the only GW merger associated with a unique host galaxy. From a
combination of GW190814, GW170814 and GW170817, our analysis yields $H_0 =
72.0^{+ 12}_{- 8.2 }~{\rm km~s^{-1}~Mpc^{-1}}$ (68\% Highest Density Interval,
HDI) for a prior in $H_0$ uniform between $[20,140]~{\rm km~s^{-1}~Mpc^{-1}}$.
The addition of GW190814 and GW170814 to GW170817 improves the 68\% HDI from
GW170817 alone by $\sim 18\%$, showing how well-localized mergers without
counterparts can provide a significant contribution to standard siren
measurements, provided that a complete galaxy catalog is available at the
location of the event. | Galaxy and Mass Assembly (GAMA): Selection of the Most Massive Clusters: We have developed a galaxy cluster finding technique based on the Delaunay
Tessellation Field Estimator (DTFE) combined with caustic analysis. Our method
allows us to recover clusters of galaxies within the mass range of 10^12 to
10^16 Msun. We have found a total of 113 galaxy clusters in the Galaxy and Mass
Assembly survey (GAMA). In the corresponding mass range, the density of
clusters found in this work is comparable to the density traced by clusters
selected by the thermal Sunyaev Zel'dovich Effect; however, we are able to
cover a wider mass range. We present the analysis of the two-point correlation
function for our cluster sample. |
The Lifetimes of Spiral Patterns in Disc Galaxies: The rate of internally-driven evolution of galaxy discs is strongly affected
by the lifetimes of the spiral patterns they support. Evolution is much faster
if the spiral patterns are recurrent short-lived transients rather than
long-lived, quasi-steady features. As rival theories are still advocated based
on these two distinct hypotheses, I review the evidence that bears on the
question of the lifetimes of spiral patterns in galaxies. Observational
evidence from external galaxies is frustratingly inconclusive, but the velocity
distribution in the solar neighbourhood is more consistent with the transient
picture. I present simulations of galaxy models that have been proposed to
support quasi-steady, two-arm spiral modes that in fact evolve quickly due to
multi-arm instabilities. I also show that all simulations to date manifest
short-lived patterns, despite claims to the contrary. Thus the transient
hypothesis is favoured by both numerical results and the velocity distribution
in the solar neighbourhood. | Quasi-isotropic expansion for a two-fluid cosmological model containing
radiation and string gas: The quasi-isotropic expansion for a simple two-fluid cosmological model,
including radiation and string gas is constructed. The first non-trivial order
expressions for the metric coefficients, energy densities and velocities are
explicitly written down. Their small and large time asymptotics are studied. It
is found that the large time asymptotic for the anisotropic component of the
metric coefficients grows faster than that of the isotropic
(trace-proportional) component. |
Can Effects of Dark Matter be Explained by the Turbulent Flow of
Spacetime?: For the past forty years the search for dark matter has been one of the
primary foci of astrophysics, although there has yet to be any direct evidence
for its existence (Porter et al. 2011). Indirect evidence for the existence of
dark matter is largely rooted in the rotational speeds of stars within their
host galaxies, where, instead of having a ~ r^1/2 radial dependence, stars
appear to have orbital speeds independent of their distance from the galactic
center, which led to proposed existence of dark matter (Porter et al. 2011;
Peebles 1993). We propose an alternate explanation for the observed stellar
motions within galaxies, combining the standard treatment of a fluid-like
spacetime with the possibility of a "bulk flow" of mass through the Universe.
The differential "flow" of spacetime could generate vorticies capable of
providing the "perceived" rotational speeds in excess of those predicted by
Newtonian mechanics. Although a more detailed analysis of our theory is
forthcoming, we find a crude "order of magnitude" calculation can explain this
phenomena. We also find that this can be used to explain the graviational
lensing observed around globular clusters like "Bullet Cluster". | Constraining jet production scenarios by studies of
Narrow-Line-Radio-Galaxies: We study a large sample of narrow-line radio galaxies (NLRGs) with extended
radio structures. Using 1.4 GHz radio luminosities, $L_{1.4}$, narrow optical
emission line luminosities, $L_{\oiii}$ and $L_{H_{\alpha}}$, as well as black
hole masses $M_{BH}$ derived from stellar velocity dispersions measured from
the optical spectra obtained with the Sloan Digital Sky Survey, we find that:
(i) NLRGs cover about 4 decades of the Eddington ratio, $\lambda \equiv
L_{bol}/L_{Edd} \propto L_{line}/M_{BH}$; (ii) $L_{1.4}/M_{BH}$ strongly
correlates with $\lambda$; (iii) radio-loudness, ${\cal R} \equiv
L_{1.4}/L_{line}$, strongly anti-correlates with $\lambda$. A very broad range
of the Eddington ratio indicates that the parent population of NLRGs includes
both radio-loud quasars (RLQs) and broad-line radio galaxies (BLRGs). The
correlations they obey and their high jet production efficiencies favor a jet
production model which involves the so-called 'magnetically choked' accretion
scenario. In this model, production of the jet is dominated by the
Blandford-Znajek mechanism, and the magnetic fields in the vicinity of the
central black hole are confined by the ram pressure of the accretion flow.
Since large net magnetic flux accumulated in central regions of the accretion
flow required by the model can take place only via geometrically thick
accretion, we speculate that the massive, 'cold' accretion events associated
with luminous emission-line AGN can be accompanied by an efficient jet
production only if preceded by a hot, very sub-Eddington accretion phase. |
Producing the Deuteron in Stars: Anthropic Limits on Fundamental
Constants: Stellar nucleosynthesis proceeds via the deuteron (D), but only a small
change in the fundamental constants of nature is required to unbind it. Here,
we investigate the effect of altering the binding energy of the deuteron on
proton burning in stars. We find that the most definitive boundary in parameter
space that divides probably life-permitting universes from probably
life-prohibiting ones is between a bound and unbound deuteron. Due to neutrino
losses, a ball of gas will undergo rapid cooling or stabilization by electron
degeneracy pressure before it can form a stable, nuclear reaction-sustaining
star. We also consider a less-bound deuteron, which changes the energetics of
the $pp$ and $pep$ reactions. The transition to endothermic $pp$ and $pep$
reactions, and the resulting beta-decay instability of the deuteron, do not
seem to present catastrophic problems for life. | The COS-Halos Survey: An Empirical Description of the Metal-Line
Absorption in the Low-Redshift Circumgalactic Medium: We present the equivalent width and column density measurements for low and
intermediate ionization states of the circumgalactic medium (CGM) surrounding
44 low-z, L ~ L* galaxies drawn from the COS-Halos survey. These measurements
are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra
of background quasars within an impact parameter R < 160 kpc to the targeted
galaxies. The data show significant metal-line absorption for 33 of the 44
galaxies, including quiescent systems, revealing the common occurance of a cool
(T ~ 10^{4 - 5} K), metal-enriched CGM. The detection rates and column
densities derived for these metal lines decrease with increasing impact
parameter, a trend we interpret as a declining metal surface density profile
for the CGM. A comparison of the relative column densities of adjacent
ionization states indicates the gas is predominantly ionized. The large surface
density in metals demands a large reservoir of metals and gas in the cool CGM
(very conservatively, M_ CGMcool > 10^9 MSun), which likely traces a distinct
density and/or temperature regime from the highly-ionized CGM traced by OVI
absorption. The large dispersion in absorption strengths (including
non-detections) suggests the cool CGM traces a wide range of densities or a mix
of local ionizing conditions. Lastly, the kinematics inferred from the
metal-line profiles are consistent with the cool CGM being bound to the dark
matters halos hosting the galaxies; this gas may serve as fuel for future
star-formation. Future work will leverage this dataset to provide estimates on
the mass, metallicity, dynamics, and origin of the cool CGM in low-z, L*
galaxies. |
Lensing convergence and anisotropic dark energy in galaxy redshift
surveys: Analyses of upcoming galaxy surveys will require careful modelling of
relevant observables such as the power spectrum of galaxy counts in harmonic
space $C_\ell(z,z')$. We investigate the impact of disregarding relevant
relativistic effects by considering a model of dark energy including constant
sound speed $c_{\rm eff}^2$, constant equation of state $w$, and anisotropic
stress sourced by matter perturbations $\pi$. Cosmological constraints were
computed using cosmic microwave background anisotropies, baryon acoustic
oscillations, supernovae type Ia, and redshift space distortions. Our results
are consistent with $w=-1$, $c_{\rm eff}^2=1$, and $\pi=0$. Then, a forecast
for the performance of an Euclid-like galaxy survey was carried out also adding
information from other probes. Here we show that, regardless of the galaxy
survey configuration, neglecting the effect of lensing convergence will lead to
substantial shifts in the galaxy bias $b_0$ and the neutrino mass $\sum m_\nu$.
Shifts in the dark energy sound speed and anisotropic stress also appear, but
they depend on the survey configuration and hence lack robustness. While
neglecting lensing convergence also leads to a Hubble constant $H_0$ moving
downwards, the significance of the shift is not big enough to play a relevant
part in the current $H_0$ tension. | Massive black hole seeds born via direct gas collapse in galaxy mergers:
their properties, statistics and environment: We study the statistics and cosmic evolution of massive black hole seeds
formed during major mergers of gas-rich late-type galaxies. Generalizing the
results of the hydro-simulations from Mayer et al. 2010, we envision a scenario
in which a supermassive star can form at the center of galaxies that just
experienced a major merger owing to a multi-scale powerful gas inflow, provided
that such galaxies live in haloes with masses above 10^{11} Msun, are gas-rich
and disc-dominated, and do not already host a massive black hole. We assume
that the ultimate collapse of the supermassive star leads to the rapid
formation of a black hole of 10^5 Msun following a quasi-star stage. Using a
model for galaxy formation applied to the outputs of the Millennium Simulation,
we show that the conditions required for this massive black hole formation
route to take place in the concordance LambdaCDM model are actually common at
high redshift, and can be realized even at low redshift. Most major mergers
above z~4 in haloes with mass > 10^{11} Msun can lead to the formation of a
massive seed and, at z~2, the fraction of favourable mergers decreases to about
half. Interestingly, we find that even in the local universe a fraction (~20%)
of major mergers in massive haloes still satisfy the conditions for our massive
black hole formation route. Those late events take place in galaxies with a
markedly low clustering amplitude, that have lived in isolation for most of
their life, and that are experiencing a major merger for the first time. We
predict that massive black hole seeds from galaxy mergers can dominate the
massive end of the mass function at high (z>4) and intermediate (z~2) redshifts
relative to lighter seeds formed at higher redshift, for example, by the
collapse of Pop III stars. Finally, a fraction of these massive seeds could
lie, soon after formation, above the MBH-MBulge relation. |
Curvature perturbation from velocity modulation: We propose a new variant model of the modulated reheating. If particles have
large scale fluctuations on their velocities, or equivalently their Lorentz
factors, the decay rate also fluctuates and the curvature perturbation is
induced via their decay processes in analogy with modulated reheating. For
example, if they are produced nonthermally by the decay of another field with
its mass fluctuating on large scales, such a situation is realized. We
explicitly calculate the resulting curvature perturbation and non-linearity
parameters and show that the effect of velocity-modulation is not negligible if
the particles are semi-relativistic at the decay. | Growth history and quasar bias evolution at z < 3 from Quaia: We make use of the Gaia-Unwise quasar catalogue, Quaia, to constrain the
growth history out to high redshifts from the clustering of quasars and their
cross-correlation with maps of the Cosmic Microwave Background (CMB) lensing
convergence. Considering three tomographic bins, centered at redshifts
$\bar{z}_i = [0.69, 1.59, 2.72]$, we reconstruct the evolution of the amplitude
of matter fluctuations $\sigma_8(z)$ over the last $\sim12$ billion years of
cosmic history. In particular, we make one of the highest-redshift measurements
of $\sigma_8$ ($\sigma_8(z=2.72)=0.22\pm 0.06$), finding it to be in good
agreement (at the $\sim1\sigma$ level) with the value predicted by $\Lambda$CDM
using CMB data from Planck. We also used the data to study the evolution of the
linear quasar bias for this sample, finding values similar to those of other
quasar samples, although with a less steep evolution at high redshifts.
Finally, we study the potential impact of foreground contamination in the CMB
lensing maps and, although we find evidence of contamination in
cross-correlations at $z\sim1.7$ we are not able to clearly pinpoint its origin
as being Galactic or extragalactic. Nevertheless, we determine that the impact
of this contamination on our results is negligible. |
Velocity bias in the distribution of dark matter halos: The standard formalism for the co-evolution of halos and dark matter predicts
that any initial halo velocity bias rapidly decays to zero. We argue that, when
the purpose is to compute statistics like power spectra etc., the coupling in
the momentum conservation equation for the biased tracers must be modified. Our
new formulation predicts the constancy in time of any statistical halo velocity
bias present in the initial conditions, in agreement with peak theory. We test
this prediction by studying the evolution of a conserved halo population in
N-body simulations. We establish that the initial simulated halo density and
velocity statistics show distinct features of the peak model and, thus, deviate
from the simple local Lagrangian bias. We demonstrate, for the first time, that
the time evolution of their velocity is in tension with the rapid decay
expected in the standard approach. | Evolution of primordial planets in relation to the cosmological origin
of life: We explore the conditions prevailing in primordial planets in the framework
of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of
condensation of planet-mass H-4He gas clouds in trillion-planet clumps is set
at 300,000 yr (0.3My) following the onset of plasma instabilities when ambient
temperatures were >1000K. Eventual collapse of the planet-cloud into a solid
structure takes place against the background of an expanding universe with
declining ambient temperatures. Stars form from planet mergers within the
clumps and die by supernovae on overeating of planets. For planets produced by
stars, isothermal free fall collapse occurs initially via quasi equilibrium
polytropes until opacity sets in due to molecule and dust formation. The
contracting cooling cloud is a venue for molecule formation and the sequential
condensation of solid particles, starting from mineral grains at high
temperatures to ice particles at lower temperatures, water-ice becomes
thermodynamically stable between 7 and 15 My after the initial onset of
collapse, and contraction to form a solid icy core begins shortly thereafter.
Primordial-clump-planets are separated by ~ 1000 AU, reflecting the high
density of the universe at 30,000 yr. Exchanges of materials, organic molecules
and evolving templates readily occur, providing optimal conditions for an
initial origin of life in hot primordial gas planet water cores when adequately
fertilized by stardust. The condensation of solid molecular hydrogen as an
extended outer crust takes place much later in the collapse history of the
protoplanet. When the object has shrunk to several times the radius of Jupiter,
the hydrogen partial pressure exceeds the saturation vapour pressure of solid
hydrogen at the ambient temperature and condensation occurs. |
Hubble/COS Observations of the Quasar HE 2347-4342: Probing the Epoch of
He II Patchy Reionization at Redshifts z = 2.4-2.9: We report ultraviolet spectra of the high-redshift (z_em = 2.9) quasar, HE
2347-4342, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space
Telescope (HST). Spectra in the G130M (medium-resolution, 1135-1440 A) and
G140L (low-resolution, 1030-2000 A) gratings exhibit patchy Gunn-Peterson
absorption in the 303.78 A (Ly-alpha) line of He II between z = 2.39-2.87
(G140L) and z = 2.74-2.90 (G130M). With COS, we obtain better spectral
resolution, higher-S/N, and better determined backgrounds than previous
studies, with sensitivity to abundance fractions x_HeII = 0.01 in filaments of
the cosmic web. The He II optical depths from COS are higher than those with
the Far Ultraviolet Spectroscopic Explorer (FUSE) and range from tau_HeII <
0.02 to tau_HeII > 5, with a slow recovery in mean optical depth, tau < 2 at z
< 2.7. The He II/H I optical-depth ratio varies (eta = 10-100 for 2.4 < z <
2.73 and eta = 5-500 for 2.75 < z < 2.89) on scales Delta z < 0.01 (10.8 Mpc in
comoving radial distance at z = 2.8), with numerous flux-transmission windows
between 1135-1186 A. The He II absorption extends to 1186.26 A (z = 2.905),
including associated absorbers with z_abs ~ z_QSO and minimal "proximity
effect" of flux transmission at the He II edge. We propose a QSO systemic
redshift z_QSO = 2.904 +/- 0.002, some Delta z = 0.019 higher than that derived
from O I (1302 A) emission. Three long troughs (4-10 A or 25-60 Mpc comoving
distance) of strong He II absorption between z = 2.75-2.90 are uncharacteristic
of the intergalactic medium if He II reionized at z_r ~ 3. Contrary to recent
indirect estimates (z_r = 3.2 +/- 0.2) from H I optical depths, the epoch of
HeII reionization may extend to z ~ 2.7. | Radiative Efficiency of Disk Accretion in Individual SDSS QSOs: We estimate the radiative efficiency (epsilon) of individual type 1 SDSS QSOs
by using their bolometric luminosities (L_{bol}) and accretion rates
(\dot{M}_{\bullet,acc}), which may be related to the assembly histories and
spins of the central massive black holes (MBHs). We estimate L_{bol} by using
the empirical spectral energy distributions of QSOs and \dot{M}_{\bullet,acc}
by fitting the observed optical luminosity(/-ies) with the thin accretion disk
model, assuming the MBH masses given by the virial mass estimator(s)
(M_{\bullet,vir}). We find an apparent correlation between epsilon and
M_{\bullet,vir}, which is strong at redshift z \la 1.8, weak at z \ga 2, and
consistent with that found by Davis & Laor (2011) for 80 PG QSOs at z \leq 0.5.
To investigate whether this correlation is intrinsic or not, we construct a
mock sample of QSOs according to the true MBH mass and Eddington ratio
distributions given in Kelly & Shen (2013). By comparing the results obtained
from the mock sample with that from the SDSS sample, we demonstrate that the
apparent epsilon-M_{\bullet,vir} correlation can be produced by and mainly due
to the selection effects of the SDSS sample and the bias induced by the usage
of M_{\bullet,vir} as the true MBH mass. The mean values of epsilon of those
SDSS QSOs are consistent with being a constant \simeq 0.11-0.16 over the
redshift range of 0.3 \la z \la 4. We conclude that the current SDSS QSO data
is consistent with no strong intrinsic correlation between radiative efficiency
and true MBH mass and no significant redshift evolution of radiative
efficiencies. |
Gamma Ray Constraints on Flavor Violating Asymmetric Dark Matter: We show how cosmic gamma rays can be used to constrain models of asymmetric
Dark Matter decaying into lepton pairs by violating flavor. First of all we
require the models to explain the anomalies in the charged cosmic rays measured
by PAMELA, FERMI and HESS; performing combined fits we determine the allowed
values of the Dark Matter mass and lifetime. For these models, we then
determine the constraints coming from the measurement of the isotropic
gamma-ray background by FERMI for a complete set of lepton flavor violating
primary modes and over a range of DM masses from 100 GeV to 10 TeV. We find
that the FERMI constraints rule out the flavor violating asymmetric Dark Matter
interpretation of the charged cosmic ray anomalies. | The contribution of massive haloes to the matter power spectrum in the
presence of AGN feedback: The clustering of matter, as measured by the matter power spectrum, informs
us about dark matter and cosmology, as well as baryonic effects on the
distribution of matter in the universe. Using cosmological hydrodynamical
simulations from the cosmo-OWLS and BAHAMAS simulation projects, we investigate
the contribution of power in haloes with various masses, defined by particles
within some overdensity region, to the full power spectrum, as well as the
power ratio between baryonic and dark matter only (DMO) simulations for a
matched (between simulations) and an unmatched set of haloes. We find that the
presence of AGN feedback suppresses the power on all scales for haloes of all
masses examined ($10^{11.25}\leq M_{500,\mathrm{crit}}\leq
10^{14.75}\,\mathrm{M_\odot}/h$), by ejecting matter from within
$r_{500,\mathrm{c}}$ to $r_{200,\mathrm{m}}$ and potentially beyond in massive
haloes ($M_{500,\mathrm{crit}}\gtrsim 10^{13}\,\mathrm{M_\odot}/h$), and likely
impeding the growth of lower-mass haloes as a consequence. A lower AGN feedback
temperature drastically changes the behaviour of high-mass haloes
($M_{500,\mathrm{crit}}\geq 10^{13.25}\,\mathrm{M_\odot}/h$), damping the
effects of AGN feedback at small scales, $k\,\gtrsim\,4\,h\mathrm{\,Mpc^{-1}}$.
For $k\,\lesssim\,3\,h\mathrm{\,Mpc^{-1}}$, group-sized haloes
($10^{14\pm0.25}\, \mathrm{M_\odot}/h$) dominate the power spectrum, while on
smaller scales the combined contributions of lower-mass haloes to the full
power spectrum rise above that of the group-sized haloes. Finally, we present a
model for the power suppression due to feedback, which combines observed mean
halo baryon fractions with halo mass fractions and halo-matter cross-spectra
extracted from dark matter only simulations to predict the power suppression to
percent-level accuracy down to $k\,\approx\,10\,h\mathrm{\,Mpc^{-1}}$ without
any free parameters. |
The Nature of Sub-millimetre Galaxies in Cosmological Hydrodynamic
Simulations: We study the nature of rapidly star-forming galaxies at z=2 in cosmological
hydrodynamic simulations, and compare their properties to observations of
sub-millimetre galaxies (SMGs). We identify simulated SMGs as the most rapidly
star-forming systems that match the observed number density of SMGs. In our
models, SMGs are massive galaxies sitting at the centres of large potential
wells, being fed by smooth infall and gas-rich satellites at rates comparable
to their star formation rates (SFR). They are not typically undergoing major
mergers that significantly boost their quiescent SFR, but they still often show
complex gas morphologies and kinematics. Our simulated SMGs have stellar masses
of log M*/Mo~11-11.7, SFRs of ~180-500 Mo/yr, a clustering length of 10 Mpc/h,
and solar metallicities. The SFRs are lower than those inferred from far-IR
data by a factor of 3, which we suggest may owe to one or more systematic
effects in the SFR calibrations. SMGs at z=2 live in ~10^13 Mo halos, and by
z=0 they mostly end up as brightest group galaxies in ~10^14 Mo halos. We
predict that higher-M* SMGs should have on average lower specific SFRs, less
disturbed morphologies, and higher clustering. We also predict that deeper
far-IR surveys will smoothly join SMGs onto the massive end of the SFR-M*
relationship defined by lower-mass z=2 galaxies. Overall, our simulated rapid
star-formers provide as good a match to available SMG data as merger-based
scenarios, offering an alternative scenario that emerges naturally from
cosmological simulations. | Superdense massive galaxies in the ESO Distant Cluster Survey (EDisCS): We find a significant number of massive and compact galaxies in clusters from
the ESO Distant Clusters Survey (EDisCS) at 0.4<z<1. They have similar stellar
masses, ages, sizes and axial ratios to local z~0.04 compact galaxies in WINGS
clusters, and to z=1.4-2 massive and passive galaxies found in the general
field. If non-BCG cluster galaxies of all densities, morphologies and spectral
types are considered, the median size of EDisCS galaxies is only a factor 1.18
smaller than in WINGS. We show that for morphologically selected samples, the
morphological evolution taking place in a significant fraction of galaxies
during the last Gyrs may introduce an apparent, spurious evolution of size with
redshift, which is actually due to intrinsic differences in the selected
samples. We conclude that the median mass-size relation of cluster galaxies
does not evolve significantly from z~0.7 to z~0.04. In contrast, the masses and
sizes of BCGs and galaxies with M*>4x10^11 Msun have significantly increased by
a factor of 2 and 4, respectively, confirming the results of a number of recent
works on the subject. Our findings show that progenitor bias effects play an
important role in the size-growth paradigm of massive and passive galaxies. |
Cosmic opacity: cosmological-model-independent tests and their impacts
on cosmic acceleration: With assumptions that the violation of the distance-duality (DD) relation
entirely arises from non-conservation of the photon number and the absorption
is frequency independent in the observed frequency range, we perform
cosmological-model-independent tests for the cosmic opacity. The observational
data include the largest Union2.1 SN Ia sample, which is taken for observed
$D_\mathrm{L}$, and galaxy cluster samples compiled by De Filippis {\it et al.}
and Bonamente {\it et al.}, which are responsible for providing observed
$D_\mathrm{A}$. Two parameterizations, $\tau(z)=2\epsilon z$ and
$\tau(z)=(1+z)^{2\epsilon}-1$ are adopted for the optical depth associated to
the cosmic absorption. We find that, an almost transparent universe is favored
by Filippis {\it et al.} sample but it is only marginally accommodated by
Bonomente {\it et al.} samples at 95.4% confidence level (C. L.) (even at 99.7%
C. L. when the $r<100 \mathrm{kpc}$-cut spherical $\beta$ model is considered).
Taking the possible cosmic absorption (in 68.3% C. L. range) constrained from
the model-independent tests into consideration, we correct the distance modulus
of SNe Ia and then use them to study their cosmological implications. The
constraints on the $\Lambda$CDM show that a decelerating expanding universe
with $\Omega_\Lambda=0$ is only allowed at 99.7% C. L. by observations when the
Bonamente {\it et al.} sample is considered. Therefore, our analysis suggests
that an accelerated cosmic expansion is still needed to account for the dimming
of SNe and the standard cosmological scenario remains to be supported by
current observations. | The Evolution of Radio Galaxies and X-ray Point Sources in Coma Cluster
Progenitors Since z~1.2: Using Chandra imaging spectroscopy and Very Large Array (VLA) L-band radio
maps, we have identified radio sources at P_{1.4GHz} >=5x10^{23} W Hz^{-1} and
X-ray point sources (XPSs) at L_{0.3-8keV}>=5x10^{42} erg s^{-1} in L>L*
galaxies in 12 high-redshift (0.4<z<1.2) clusters of galaxies. The radio
galaxies and XPSs in this cluster sample, chosen to be consistent with Coma
Cluster progenitors at these redshifts, are compared to those found at low-z
analyzed in Hart et al. (2009). Within a projected radius of 1 Mpc of the
cluster cores, we find 17 cluster radio galaxies (11 with secure redshifts,
including one luminous FR II radio source at z=0.826, and 6 more with host
galaxy colors similar to cluster ellipticals). The radio luminosity function
(RLF) of the cluster radio galaxies as a fraction of the cluster red sequence
(CRS) galaxies reveals significant evolution of this population from high-z to
low-z, with higher power radio galaxies situated in lower temperature clusters
at earlier epochs. Additionally, there is some evidence that cluster radio
galaxies become more centrally concentrated than CRS galaxies with cosmic time.
Within this same projected radius, we identify 7 spectroscopically-confirmed
cluster XPSs, all with CRS host galaxy colors. Consistent with the results from
Martini et al. (2009), we estimate a minimum X-ray active fraction of
1.4+/-0.8% for CRS galaxies in high-z clusters, corresponding to an approximate
10-fold increase from 0.15+/-0.15% at low-z. Although complete redshift
information is lacking for several XPSs in z>0.4 cluster fields, the increased
numbers and luminosities of the CRS radio galaxies and XPSs suggest a
substantial (9-10 fold) increase in the heat injected into high redshift
clusters by AGN compared to the present epoch. |
The Swift X-ray Telescope Cluster Survey III: Cluster Catalog from
2005-2012 Archival Data: We present the Swift X-ray Cluster Survey (SWXCS) catalog obtained using
archival data from the X-ray telescope (XRT) on board the Swift satellite
acquired from 2005 to 2012, extending the first release of the SWXCS. The
catalog provides positions, soft fluxes, and, when possible, optical
counterparts for a flux-limited sample of X-ray group and cluster candidates.
We consider the fields with Galactic latitude |b| > 20 degree to avoid high HI
column densities. We discard all of the observations targeted at groups or
clusters of galaxies, as well as particular extragalactic fields not suitable
to search for faint extended sources. We finally select ~3000 useful fields
covering a total solid angle of ~400 degree^2. We identify extended source
candidates in the soft-band (0.5-2keV) images of these fields using the
software EXSdetect, which is specifically calibrated for the XRT data.
Extensive simulations are used to evaluate contamination and completeness as a
function of the source signal, allowing us to minimize the number of spurious
detections and to robustly assess the selection function. Our catalog includes
263 candidate galaxy clusters and groups down to a flux limit of 7E-15
erg/cm^2/s in the soft band, and the logN-logS is in very good agreement with
previous deep X-ray surveys. The final list of sources is cross-correlated with
published optical, X-ray, and SZ catalogs of clusters. We find that 137 sources
have been previously identified as clusters, while 126 are new detections.
Currently, we have collected redshift information for 158 sources (60% of the
entire sample). Once the optical follow-up and the X-ray spectral analysis of
the sources are complete, the SWXCS will provide a large and well-defined
catalog of groups and clusters of galaxies to perform statistical studies of
cluster properties and tests of cosmological models. | The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole
Masses from Reverberation Mapping of Hbeta: We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission. We present here the light curves for the objects in this sample
and the subsequent Hbeta time lags for the nine objects where these
measurements were possible. The Hbeta lag time is directly related to the size
of the broad-line region, and by combining the lag time with the measured width
of the Hbeta emission line in the variable part of the spectrum, we determine
the virial mass of the central supermassive black hole in these nine AGNs. The
absolute calibration of the black hole masses is based on the normalization
derived by Onken et al. We also examine the time lag response as a function of
velocity across the Hbeta line profile for six of the AGNs. The analysis of
four leads to ambiguous results with relatively flat time lags as a function of
velocity. However, SBS 1116+583A exhibits a symmetric time lag response around
the line center reminiscent of simple models for circularly orbiting broad-line
region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most
easily explained by a simple gravitational infall model. Further investigation
will be necessary to fully understand the constraints placed on physical models
of the BLR by the velocity-resolved response in these objects. |
Validating a novel angular power spectrum estimator using simulated low
frequency radio-interferometric data: The "Tapered Gridded Estimator" (TGE) is a novel way to directly estimate the
angular power spectrum from radio-interferometric visibility data that reduces
the computation by efficiently gridding the data, consistently removes the
noise bias, and suppresses the foreground contamination to a large extent by
tapering the primary beam response through an appropriate convolution in the
visibility domain. Here we demonstrate the effectiveness of TGE in recovering
the diffuse emission power spectrum through numerical simulations. We present
details of the simulation used to generate low frequency visibility data for
sky model with extragalactic compact radio sources and diffuse Galactic
synchrotron emission. We then use different imaging strategies to identify the
most effective option of point source subtraction and to study the underlying
diffuse emission. Finally, we apply TGE to the residual data to measure the
angular power spectrum, and assess the impact of incomplete point source
subtraction in recovering the input power spectrum $C_{\ell}$ of the
synchrotron emission. This estimator is found to successfully recovers the
$C_{\ell}$ of input model from the residual visibility data. These results are
relevant for measuring the diffuse emission like the Galactic synchrotron
emission. It is also an important step towards characterizing and removing both
diffuse and compact foreground emission in order to detect the redshifted $21\,
{\rm cm}$ signal from the Epoch of Reionization. | Global environmental effects versus galaxy interactions: We explore properties of close galaxy pairs and merging systems selected from
the SDSS-DR4 in different environments with the aim to assess the relative
importance of the role of interactions over global environmental processes. For
this purpose, we perform a comparative study of galaxies with and without close
companions as a function of local density and host-halo mass, carefully
removing sources of possible biases. We find that at low and high local density
environments, colours and morphologies of close galaxy pairs are very similar
to those of isolated galaxies. At intermediate densities, we detect significant
differences, indicating that close pairs could have experienced a more rapid
transition onto the red sequence than isolated galaxies. The presence of a
correlation between colours and morphologies indicates that the physical
mechanism responsible for the colour transformation also operates changing
galaxy morphologies. Regardless of dark matter halo mass, we show that the
percentage of red galaxies in close pairs and in the control sample are
comparable at low and high local density environments. However, at intermediate
local densities, the gap in the red fraction between close pairs and the
control galaxies increases from ~10% in low mass haloes up to ~50% in the most
massive ones. Our findings suggest that in intermediate density environments
galaxies are efficiently pre-processed by close encounters and mergers before
entering higher local density regions. (Abridge) |
PBH in single field inflation: the effect of shape dispersion and
non-Gaussianities: Primordial black holes (PBHs) may result from high peaks in a random field of
cosmological perturbations. In single field inflationary models, such
perturbations can be seeded as the inflaton overshoots a small barrier on its
way down the potential. PBHs are then produced through two distinct mechanisms,
during the radiation era. The first one is the familiar collapse of large
adiabatic overdensities. The second one is the collapse induced by relic
bubbles where the inflaton field is trapped in a false vacuum, due to large
backward fluctuations which prevented horizon sized regions from overshooting
the barrier. We consider (numerically and analytically) the effect of
non-Gaussianities on the threshold for overdensities to collapse into a PBH.
Since typical high peaks have some dispersion in their shape or profile, we
also consider the effect of such dispersion on the corresponding threshold for
collapse. With these results we estimate the most likely channel for PBH
production as a function of the non-Gaussianity parameter $f_{\rm NL}$. We also
compare the threshold for collapse coming from the perturbative versus the non
perturbative template for the non-Gaussianity arising in this model. We show
that i) for $f_{\rm NL}\gtrsim 3.5$, the population of PBH coming from false
vacuum regions dominates over that which comes from the collapse of large
adiabatic overdensities, ii) the non-perturbative template of the
non-Gaussianities is important to get accurate results. iii) the effect of the
dispersion is small in determining the threshold for the compaction function,
although it can be appreciable in determining the threshold amplitude for the
curvature perturbation at low $f_{\rm NL}$. We also confirm that the volume
averaged compaction function provides a very accurate universal estimator for
the threshold. | Why Are AGN and Host Galaxies Misaligned?: It is well-established observationally that the characteristic angular
momentum axis on small scales around AGN, traced by radio jets and the putative
torus, is not well-correlated with the large-scale angular momentum axis of the
host galaxy. In this paper, we show that such misalignments arise naturally in
high-resolution simulations in which we follow angular momentum transport and
inflows from galaxy to sub-pc scales near AGN, triggered either during galaxy
mergers or by instabilities in isolated disks. Sudden misalignments can
sometimes be caused by single massive clumps falling into the center slightly
off-axis, but more generally, they arise even when the gas inflows are smooth
and trace only global gravitational instabilities. When several nested,
self-gravitating modes are present, the inner ones can precess and tumble in
the potential of the outer modes. Resonant angular momentum exchange can flip
or re-align the spin of an inner mode on a short timescale, even without the
presence of massive clumps. We therefore do not expect that AGN and their host
galaxies will be preferentially aligned, nor should the relative alignment be
an indicator of the AGN fueling mechanism. We discuss implications of this
conclusion for AGN feedback and BH spin evolution. The misalignments may mean
that even BHs accreting from smooth large-scale disks will not be spun up to
maximal rotation, and so have more modest radiative efficiencies and
inefficient jet formation. Even more random orientations are possible if there
is further, un-resolved clumpiness in the gas, and more ordered accretion may
occur if the inflow is slower and not self-gravitating. |
(Nearly) Model-Independent Constraints on the Neutral Hydrogen Fraction
in the Intergalactic Medium at $z\sim 5-7$ Using Dark Pixel Fractions in
Ly$α$ and Ly$β$ Forests: Cosmic reionization was the last major phase transition of hydrogen from
neutral to highly ionized in the intergalactic medium (IGM). Current
observations show that the IGM is significantly neutral at $z>7$, and largely
ionized by $z\sim5.5$. However, most methods to measure the IGM neutral
fraction are highly model-dependent, and are limited to when the
volume-averaged neutral fraction of the IGM is either relatively low
($\bar{x}_{\rm HI} \lesssim 10^{-3}$) or close to unity ($\bar{x}_{\rm HI}\sim
1$). In particular, the neutral fraction evolution of the IGM at the critical
redshift range of $z=6-7$ is poorly constrained. We present new constraints on
$\bar{x}_{\rm HI}$ at $z\sim5.1-6.8$, by analyzing deep optical spectra of $53$
quasars at $5.73<z<7.09$. We derive model-independent upper limits on the
neutral hydrogen fraction based on the fraction of "dark" pixels identified in
the Lyman $\alpha$ (Ly$\alpha$) and Lyman $\beta$ (Ly$\beta$) forests, without
any assumptions on the IGM model or the intrinsic shape of the quasar
continuum. They are the first model-independent constraints on the IGM neutral
hydrogen fraction at $z\sim6.2-6.8$ using quasar absorption measurements. Our
results give upper limits of $\bar{x}_{\rm HI}(z=6.3) < 0.79\pm0.04$
(1$\sigma$), $\bar{x}_{\rm HI} (z=6.5) < 0.87\pm0.03$ (1$\sigma$), and
$\bar{x}_{\rm HI} (z=6.7) < 0.94^{+0.06}_{-0.09}$ (1$\sigma$). The dark pixel
fractions at $z>6.1$ are consistent with the redshift evolution of the neutral
fraction of the IGM derived from the Planck 2018. | Isotropy in the two-point angular correlation function of the CMB: We study the directional dependence of the angular two-point correlation
function in maps of the cosmic microwave background (CMB). We propose two new
statistics, one which measures the correlation of each point in the sky with a
ring of points separated angle theta away, and a second that measures the
missing angular correlation above 60 degrees as a function of direction. Using
these statistics, we find that most of the low power in cut-sky maps measured
by the WMAP experiment comes from unusually low contributions from the
directions of the lobes of the quadrupole and the octupole. These findings may
aid a future explanation of why the CMB exhibits low power at large angular
scales. |
Neutrino Oscillations form Cosmic Sources: a Nu Window to Cosmology: In this essay we extend the standard discussion of neutrino oscillations to
astrophysical neutrinos propagating through expanding space. This extension
introduces a new cosmological parameter $I$ into the oscillation phase. The new
parameter records cosmic history in much the same manner as the redshift z or
the apparent luminosity D_L. Measuring $I$ through neutrino oscillations could
help determine cosmological parameters and discriminate among different
cosmologies. | Photometric properties of Ly alpha emitters at z=4.86 in the COSMOS 2
square degree field: We present results of a survey for Ly alpha emitters at z=4.86 based on
optical narrowband (lambda_c=7126 angstrom, Delta lambda=73 angstrom) and
broadband (B, V, r', i', and z') observations of the Cosmic Evolution Survey
(COSMOS) field using Suprime-Cam on the Subaru Telescope. We find 79 LAE
candidates at z=4.86 over a contiguous survey area of 1.83 deg^2, down to the
Ly alpha line flux of 1.47 x 10^-17 ergs s^-1 cm^-2. We obtain the Ly alpha
luminosity function with a best-fit Schechter parameters of log
L^*=42.9^+0.5_-0.3 ergs s^-1 and phi^* = 1.2^+8.0_-1.1 x 10^-4 Mpc^-3 for
alpha=-1.5 (fixed). The two-point correlation function for our LAE sample is
xi(r) = (r/4.4^+5.7_-2.9 Mpc)^-1.90+/-0.22. In order to investigate the
field-to-field variations of the properties of Ly alpha emitters, we divide the
survey area into nine tiles of 0.5^circ x 0.5^circ each. We find that the
number density varies with a factor of ~ 2 from field to field with high
statistical significance. However, we find no significant field-to-field
variance when we divide the field into four tiles with 0.7^circ x 0.7^circ
each. We conclude that at least 0.5 deg^2 survey area is required to derive
averaged properties of LAEs at z~5, and our survey field is wide enough to
overcome the cosmic variance. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.