anchor
stringlengths 50
3.92k
| positive
stringlengths 55
6.16k
|
|---|---|
The nature of growing bulges within z < 1.3 galaxy disks in the GOODS-N
field: We analyze central surface brightness mu_0, nuclear and global colors of
intermediate redshift disk galaxies. On an apparent-diameter limited sample of
398 galaxies from ACS/HST Great Observatories Origins Deep Survey North
(GOODS-N), we find 131 galaxies with bulges and 214 without. Up to z ~ 0.8,
blue, star-forming nuclei are found in galaxies with low mu_0 only; all
high-mu_0 nuclei show red, passive colors, so that nuclear and global (U - B)
colors strongly correlate with central surface brightness, as found in the
local Universe. At 0.8 < z < 1.3, a fraction ~ 27% of the high-surface
brightness nuclei show blue colors, and positive nuclear color gradients. The
associated nuclear star formation must lead to bulge growth inside disks.
Population modeling suggests that such blue bulges evolve into local
pseudobulges rather than classical bulges. We do not find evidence for
rejuvenation of classical bulges at the sampled z. High luminosity AGNs become
common at 0.8 < z < 1.3, perhaps pointing to a role of AGN in the growth or
star formation truncation of bulges. | Swirling around filaments: are large-scale structure vortices spinning
up dark halos?: The kinematic analysis of dark matter and hydrodynamical simulations suggests
that the vorticity in large-scale structure is mostly confined to, and
predominantly aligned with their filaments, with an excess of probability of 20
per cent to have the angle between vorticity and filaments direction lower than
60 degrees relative to random orientations. The cross sections of these
filaments are typically partitioned into four quadrants with opposite vorticity
sign, arising from multiple flows, originating from neighbouring walls. The
spins of halos embedded within these filaments are consistently aligned with
this vorticity for any halo mass, with a stronger alignment for the most
massive structures up to an excess of probability of 165 per cent. On large
scales, adiabatic/cooling hydrodynamical simulations display the same vorticity
in the gas as in the dark matter. The global geometry of the flow within the
cosmic web is therefore qualitatively consistent with a spin acquisition for
smaller halos induced by this large-scale coherence, as argued in Codis et al.
(2012). In effect, secondary anisotropic infall (originating from the
vortex-rich filament within which these lower-mass halos form) dominates the
angular momentum budget of these halos. The transition mass from alignment to
orthogonality is related to the size of a given multi-flow region with a given
polarity. This transition may be reconciled with the standard tidal torque
theory if the latter is augmented so as to account for the larger scale
anisotropic environment of walls and filaments. |
Modeling the dust Spectral Energy Distribution of NGC 4214: We have carried out a detailed modeling of the dust Spectral Energy
Distribution (SED) of the nearby, starbursting dwarf galaxy NGC 4214. A key
point of our modeling is that we distinguish the emission from (i) HII regions
and their associated photodissociation regions (PDRs) and (ii) diffuse dust.
For both components we apply templates from the literature calculated with a
realistic geometry and including radiation transfer. The large amount of
existing data from the ultraviolet (UV) to the radio allows the direct
measurement of most of the input parameters of the models. We achieve a good
fit for the total dust SED of NGC 4214. In the present contribution we describe
the available data, the data reduction and the determination of the model
parameters, whereas a description of the general outline of our work is
presented in the contribution of Lisenfeld et al. in this volume. | Galaxy-Mass Correlations on 10 Mpc Scales in the Deep Lens Survey: We examine the projected correlation of galaxies with mass from small scales
(<few hundred kpc) where individual dark matter halos dominate, out to 15 Mpc
where correlated large-scale structure dominates. We investigate these profiles
as a function of galaxy luminosity and redshift. Selecting 0.8 million galaxies
in the Deep Lens Survey, we use photometric redshifts and stacked weak
gravitational lensing shear tomography out to radial scales of 1 degree from
the centers of foreground galaxies. We detect correlated mass density from
multiple halos and large-scale structure at radii larger than the virial
radius, and find the first observational evidence for growth in the galaxy-mass
correlation on 10 Mpc scales with decreasing redshift and fixed range of
luminosity. For a fixed range of redshift, we find a scaling of projected halo
mass with rest-frame luminosity similar to previous studies at lower redshift.
We control systematic errors in shape measurement and photometric redshift,
enforce volume completeness through absolute magnitude cuts, and explore
residual sample selection effects via simulations. |
Isocurvature perturbations in extra radiation: Recent cosmological observations, including measurements of the CMB
anisotropy and the primordial helium abundance, indicate the existence of an
extra radiation component in the Universe beyond the standard three neutrino
species. In this paper we explore the possibility that the extra radiation has
isocurvatrue fluctuations. A general formalism to evaluate isocurvature
perturbations in the extra radiation is provided in the mixed inflaton-curvaton
system, where the extra radiation is produced by the decay of both scalar
fields. We also derive constraints on the abundance of the extra radiation and
the amount of its isocurvature perturbation. Current observational data favors
the existence of an extra radiation component, but does not indicate its having
isocurvature perturbation. These constraints are applied to some particle
physics motivated models. If future observations detect isocurvature
perturbations in the extra radiation, it will give us a hint to the origin of
the extra radiation. | Central radio galaxies in galaxy clusters: Joint surveys by eROSITA and
ASKAP: The extended ROentgen Survey with an Imaging Telescope Array (eROSITA)
telescope onboard the Spectrum-Roentgen-Gamma (SRG) mission has finished the
first eROSITA All-Sky Survey (eRASS:1), and detected 10$^4$ galaxy clusters in
the western Galactic hemisphere. In the radio band, the Australian Square
Kilometre Array Pathfinder (ASKAP) telescope finished its pilot 1 phase of the
project 'Evolutionary Map of the Universe' (EMU) with 220.000 sources in a 270
deg$^2$ field overlapping with eRASS:1. These two surveys are used to study
radio-mode Active Galactic Nuclei (AGN) in clusters. In order to understand the
efficiency of radio-mode feedback at the centers of galaxy clusters, we relate
the radio properties of brightest cluster galaxies (BCG) to the X-ray
properties of the host clusters. We identify the central radio sources in
eRASS:1 clusters or calculate corresponding upper limits on the radio
luminosity. Then, we derive relations between the X-ray properties of the
clusters and the radio properties of the corresponding central radio source. We
also apply a mid-infrared color criterion using WISE colors to identify AGN. In
total we investigate a sample of 75 clusters. We find a statistically
significant correlation between the X-ray luminosity of the cluster and the 944
MHz radio luminosity of the corresponding central radio galaxy. There is also a
positive trend between the radio power and the largest linear size (LLS) of the
radio source. The density and the LLS do not show any correlation. We find that
in high luminosity clusters with L_X > $10^{43}$ erg s$^{-1}$ the kinetic
luminosity of the radio jets is not longer correlated with the X-ray luminosity
and discuss various reasons. We find an anti-correlation between the central
cooling time t_cool and the radio luminosity L_R indicating a need for more
powerful AGN in clusters with short central cooling times. |
Integral field spectroscopy of HII regions in M33: Integral field spectroscopy (IFS) is presented for star forming regions in
M33. A central area of 300 x 500 pc^2 and the external HII region IC 132, at a
galactocentric distance {\sim} 19arcmin (4.69 kpc) were observed with the
Potsdam Multi Aperture Spectrophotometer (PMAS) instrument at the 3.5 m
telescope of the Calar Alto Hispano- Alem\'an observatory (CAHA). The spectral
coverage goes from 3600 A to 1{\mu}m to include from [OII]{\lambda}3727 A to
the near infrared lines required for deriving sulphur electron temperature and
abundance diagnostics. Local conditions within individual HII regions are
presented in the form of emission line fluxes and physical conditions for each
spatial resolution element (spaxel) and for segments with similar H{\alpha}
surface brightness. A clear dichotomy is observed when comparing the central to
outer disc HII regions. While the external HII region has higher electron
temperature plus larger H{\beta} equivalent width, size and excitation, the
central region has higher extinction and metal content. The dichotomy extends
to the BPT diagnostic diagrams that show two orthogonal broad distributions of
points. By comparing with pseudo-3D photoionization models we conclude that the
bulk observed differences are probably related to a different ionization
parameter and metallicity. Wolf-Rayet features are detected in IC 132, and
resolved into two concentrations whose integrated spectra were used to estimate
the characteristic number of WR stars. No WR features were detected in the
central HII regions despite their higher metallicity. | Probing Dark Energy in The scope of Bianchi type I Spacetime: It is well known that flat FRW metric is a special case of Bianchi type I
spacetime. In this paper, we use 38 Hubble parameter, $H(z)$, measurements at
intermediate redshifts $0.07\leq z\leq 2.36$ and its joint combination with the
latest \textgravedbl joint light curves\textacutedbl (JLA) sample, comprised of
740 type Ia supernovae in the redshift range $z \epsilon [0.01, 1.30]$ to
constrain the parameters of Bianchi type I dark energy model. We also use the
same datasets to constrain flat $\Lambda$CDM Model. In both cases, we
specifically address the expansion rate $H_{0}$ as well as the transition
redshift $z_{t}$ determinations out of these measurements. In both Models we
found that using joint combination of datasets gives rise to lower values for
model parameters. Also to compare the considered cosmologies, we have made
Akaike information criterion (AIC) and Bayes factor ($\Psi$) tests. |
Improving three-dimensional mass mapping with weak gravitational lensing
using galaxy clustering: The weak gravitational lensing distortion of distant galaxy images (defined
as sources) probes the projected large-scale matter distribution in the
Universe. To improve quality in the 3D mass mapping using 3D-lensing, we
combine the lensing information with the spatial clustering of a population of
galaxies that trace the matter density with a known galaxy bias (defined as
tracers). For our minimum variance estimator, merely all the second-order bias
of the tracers has to be known, which can in principle be self-consistently
constrained in the data by lensing techniques. This synergy introduces a new
noise component because of the stochasticity in the matter-tracer density
relation. We give a description of the stochasticity noise in the Gaussian
regime, and we investigate the estimator characteristics analytically. We apply
the estimator to a mock survey based on the Millennium Simulation. The
estimator linearly mixes the individual lensing mass and tracer number density
maps into a combined smoothed mass map. The weighting in the mix depends on the
S/N of the individual maps and the correlation, $r$, between the matter and
galaxy density. The weight of the tracers can be reduced by hand. For moderate
mixing, the S/N in the mass map improves by a factor $\sim2-3$ for
$r\gtrsim0.4$; the systematic offset between a true and apparent mass peak
distance ($z$-shift bias) in a lensing-only map is eliminated, even for weak
correlations of $r\sim0.4$. If the second-order bias of tracer galaxies can be
determined, the synergy technique potentially provides an option to improve
redshift accuracy and completeness of the lensing 3D mass map. However,the
estimator's performance on sub-degree, non-Gaussian scales depends on all
details in the galaxy bias mechanism and, hence, its accuracy on the choice of
the tracer population.[abridged] | The Birth of a Galaxy. II. The Role of Radiation Pressure: Massive stars provide feedback that shapes the interstellar medium of
galaxies at all redshifts and their resulting stellar populations. Here we
present three adaptive mesh refinement radiation hydrodynamics simulations that
illustrate the impact of momentum transfer from ionising radiation to the
absorbing gas on star formation in high-redshift dwarf galaxies. Momentum
transfer is calculated by solving the radiative transfer equation with a ray
tracing algorithm that is adaptive in spatial and angular coordinates. We find
that momentum input partially affects star formation by increasing the
turbulent support to a three-dimensional rms velocity equal to the circular
velocity of early haloes. Compared to a calculation that neglects radiation
pressure, the star formation rate is decreased by a factor of five to 1.8 x
10^{-2} Msun/yr in a dwarf galaxy with a dark matter and stellar mass of 2.0 x
10^8 and 4.5 x 10^5 solar masses, respectively, when radiation pressure is
included. Its mean metallicity of 10^{-2.1} Z_sun is consistent with the
observed dwarf galaxy luminosity-metallicity relation. However, what one may
naively expect from the calculation without radiation pressure, the central
region of the galaxy overcools and produces a compact, metal-rich stellar
population with an average metallicity of 0.3 Z_sun, indicative of an incorrect
physical recipe. In addition to photo-heating in HII regions, radiation
pressure further drives dense gas from star forming regions, so supernovae
feedback occurs in a warmer and more diffuse medium, launching metal-rich
outflows. Capturing this aspect and a temporal separation between the start of
radiative and supernova feedback are numerically important in the modeling of
galaxies to avoid the "overcooling problem". We estimate that dust in early
low-mass galaxies is unlikely to aid in momentum transfer from radiation to the
gas. |
On the Velocity in the Effective Field Theory of Large Scale Structures: We compute the renormalized two-point functions of density, divergence and
vorticity of the velocity in the Effective Field Theory of Large Scale
Structures. Because of momentum and mass conservation, the corrections from
short scales to the large-scale power spectra of density, divergence and
vorticity must start at order $k^{4}$. For the vorticity this constitutes one
of the two leading terms. Exact (approximated) self-similarity of an
Einstein-de Sitter ($\Lambda$CDM) background fixes the time dependence so that
the vorticity power spectrum at leading order is determined by the symmetries
of the problem and the power spectrum around the non-linear scale. We show that
to cancel all divergences in the velocity correlators one needs new
counterterms. These fix the definition of velocity and do not represent new
properties of the system. For an Einstein-de Sitter universe, we show that all
three renormalized cross- and auto-correlation functions have the same
structure but different numerical coefficients, which we compute. We elucidate
the differences between using momentum and velocity. | Constraining cosmic curvature by using age of galaxies and gravitational
lenses: We use two model-independent methods to constrain the curvature of the
universe. In the first method, we study the evolution of the curvature
parameter ($\Omega_k^0$) with redshift by using the observations of the Hubble
parameter and transverse comoving distances obtained from the age of galaxies.
Secondly, we also use an indirect method based on the mean image separation
statistics of gravitationally lensed quasars. The basis of this methodology is
that the average image separation of lensed images will show a positive,
negative or zero correlation with the source redshift in a closed, open or flat
universe respectively. In order to smoothen the datasets used in both the
methods, we use a non-parametric method namely, Gaussian Process (GP). Finally
from first method we obtain $\Omega_k^0= 0.025\pm0.57$ for a presumed flat
universe while the cosmic curvature remains constant throughout the redshift
region $0<z<1.37$ which indicates that the universe may be homogeneous.
Moreover, the combined result from both the methods suggests that the universe
is marginally closed. However, a flat universe can be incorporated at $3\sigma$
level. |
Models of Accretion Disks: An accretion flow onto a supermassive black hole is the primary process
powering quasars. However, a geometry of this flow is not well constrained.
Both global MHD simulations and observations suggest that there are several
emission components present in the nucleus: an accretion disk, hot plasma
(corona or sphere) with electrons scattering the optical and UV photons, and an
outflow (wind/jet). The relative location and size of these emission
components, as well as their "interplay" affect the emerging quasar spectrum. I
review briefly standard accretion disk models and the recent progress, point
out discrepancies between the predicted and observed spectra and discuss some
issues in fitting these models to the broad-band spectral energy distribution
of quasars. I present examples of models fitted simultaneously to the
optical-UV-X-ray data and possible constraints on the parameters. | Strongest model-independent bound on the lifetime of Dark Matter: Dark Matter is essential for structure formation in the late Universe so it
must be stable on cosmological time scales. But how stable exactly? Only
assuming decays into relativistic particles, we report an otherwise model
independent bound on the lifetime of Dark Matter using current cosmological
data. Since these decays affect only the low-$\ell$ multipoles of the CMB, the
Dark Matter lifetime is expected to correlate with the tensor-to-scalar ratio
$r$ as well as curvature $\Omega_k$. We consider two models, including $r$ and
$r+\Omega_k$ respectively, versus data from Planck, WMAP, WiggleZ and Baryon
Acoustic Oscillations, with or without the BICEP2 data (if interpreted in terms
of primordial gravitational waves). This results in a lower bound on the
lifetime of CDM given by 160Gyr (without BICEP2) or 200Gyr (with BICEP2) at 95%
confidence level. |
Multi-messenger approaches to binary supermassive black holes in the
"continuous-wave" regime: Pulsar timing arrays are sensitive to gravitational waves from supermassive
black hole (SMBH) binaries at orbital separations of << 1pc. There is currently
an observational paucity of such systems, although they are central figures in
studies of galaxy evolution, merger dynamics, and active nucleus formation. We
review the prospects of detecting SMBH binaries through electromagnetic
radiative processes thought to be associated with galaxy mergers and late-stage
binary evolution. We then discuss the scientific goals of joint pulsar timing
and electromagnetic studies of these systems, including the facilitation of
binary parameter estimation, identifying galactic hosts of gravitational wave
emitters, and relevant studies of merger dynamics and cosmology. The use of
upcoming high-precision timing arrays with the International Pulsar Timing
Array and the Square Kilometre Array, combined with ongoing electromagnetic
observing campaigns to identify active SMBH binaries, provide generous
possibilities for multi-messenger astrophysics in the near future. | Weak lensing and dark energy: the impact of dark energy on nonlinear
dark matter clustering: We examine the influence of percent-level dark energy corrections to the
nonlinear matter power spectrum on constraints of the dark energy equation of
state from future weak lensing probes. We explicitly show that a poor
approximation (off by > 10%) to the nonlinear corrections causes a > 1 sigma
bias on the determination of the dark energy equation of state. Future weak
lensing surveys must therefore incorporate dark energy modifications to the
nonlinear matter power spectrum accurate to the percent-level, to avoid
introducing significant bias in their measurements. For the WMAP5 cosmology,
the more accurate power spectrum is more sensitive to dark energy properties,
resulting in a factor of two improvement in dark energy equation of state
constraints. We explore the complementary constraints on dark energy from
future weak lensing and supernova surveys. A space-based, JDEM-like survey
measures the equation of state in five independent redshift bins to ~10%, while
this improves to ~5% for a wide-field ground-based survey like LSST. These
constraints are contingent upon our ability to control weak lensing systematic
uncertainties to the sub-percent level. |
Host Galaxy Spectra and Consequences for SN Typing From The SDSS SN
Survey: We present the spectroscopy from 5254 galaxies that hosted supernovae (SNe)
or other transient events in the Sloan Digital Sky Survey II (SDSS-II).
Obtained during SDSS-I, SDSS-II, and the Baryon Oscillation Spectroscopic
Survey (BOSS), this sample represents the largest systematic, unbiased,
magnitude limited spectroscopic survey of supernova (SN) host galaxies. Using
the host galaxy redshifts, we test the impact of photometric SN classification
based on SDSS imaging data with and without using spectroscopic redshifts of
the host galaxies. Following our suggested scheme, there are a total of 1166
photometrically classified SNe Ia when using a flat redshift prior and 1126 SNe
Ia when the host spectroscopic redshift is assumed. For 1024 (87.8%) candidates
classified as likely SNe Ia without redshift information, we find that the
classification is unchanged when adding the host galaxy redshift. Using
photometry from SDSS imaging data and the host galaxy spectra, we also report
host galaxy properties for use in future nalysis of SN astrophysics. Finally,
we investigate the differences in the interpretation of the light curve
properties with and without knowledge of the redshift. When using the SALT2
light curve fitter, we find a 21% increase in the number of fits that converge
when using the spectroscopic redshift. Without host galaxy redshifts, we find
that SALT2 light curve fits are systematically biased towards lower photometric
redshift estimates and redder colors in the limit of low signal-to-noise data.
The general improvements in performance of the light curve fitter and the
increased diversity of the host galaxy sample highlights the importance of host
galaxy spectroscopy for current photometric SN surveys such as the Dark Energy
Survey and future surveys such as the Large Synoptic Survey Telescope. | Multiwavelength campaign on Mrk 509. III. The 600 ks RGS spectrum:
unravelling the inner region of an AGN: We present the results of our 600 ks RGS observation as part of the
multiwavelength campaign on Mrk 509. The very high quality of the spectrum
allows us to investigate the ionized outflow with an unprecedented accuracy due
to the long exposure and the use of the RGS multipointing mode. We detect
multiple absorption lines from the interstellar medium and from the ionized
absorber in Mrk 509. A number of emission components are also detected,
including broad emission lines consistent with an origin in the broad line
region, the narrow OVII forbidden emission line and also (narrow) radiative
recombination continua. The ionized absorber consists of two velocity
components (v = -13 \pm 11 km/s and v = -319 \pm 14 km/s), which both are
consistent with earlier results, including UV data. There is another tentative
component outflowing at high velocity, -770 \pm 109 km/s, which is only seen in
a few highly ionized absorption lines. The outflow shows discrete ionization
components, spanning four orders of magnitude in ionization parameter. Due to
the excellent statistics of our spectrum, we demonstrate for the first time
that the outflow in Mrk 509 in the important range of log xi between 1-3 cannot
be described by a smooth, continuous absorption measure distribution, but
instead shows two strong, discrete peaks. At the highest and lowest ionization
parameters we cannot differentiate smooth and discrete components. |
The joint statistics of mildly non-linear cosmological densities and
slopes in count-in-cells: In the context of count-in-cells statistics, the joint probability
distribution of the density in two concentric spherical shells is predicted
from first first principle for sigmas of the order of one. The agreement with
simulation is found to be excellent. This statistics allows us to deduce the
conditional one dimensional probability distribution function of the slope
within under dense (resp. overdense) regions, or of the density for positive or
negative slopes. The former conditional distribution is likely to be more
robust in constraining the cosmological parameters as the underlying dynamics
is less evolved in such regions. A fiducial dark energy experiment is
implemented on such counts derived from Lambda-CDM simulations. | Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps: Supermassive black hole binary systems (SMBHB) are standard sirens -- the
gravitational wave analogue of standard candles -- and if discovered by
gravitational wave detectors, they could be used as precise distance
indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB
signals, seriously degrading any distance measurements. Using a weak lensing
map of the SMBHB line of sight, we can estimate its magnification and thereby
remove some uncertainty in its distance, a procedure we call "delensing." We
find that delensing is significantly improved when galaxy shears are combined
with flexion measurements, which reduce small-scale noise in reconstructed
magnification maps. Under a Gaussian approximation, we estimate that delensing
with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce
distance errors by about 30-40% for a SMBHB at z=2. Including an additional
wide shear map from a space survey telescope could reduce distance errors by
50%. Such improvement would make SMBHBs considerably more valuable as
cosmological distance probes or as a fully independent check on existing
probes. |
New Bounds on Dark Energy Induced Fifth Forces: We consider the gravitational Wilsonian effective action at low energy when
all the particles of the standard model have decoupled. When the ${\cal R}^2$
terms dominate, the theory is equivalent to a scalar-tensor theory with the
universal coupling $\beta=1/\sqrt 6$ to matter for which we present strong
lower and upper bounds on the scalaron mass $m$ obtained by using results from
the E\"ot-Wash experiment on the modification of the inverse-square law, the
observations of the hot gas of galaxy clusters and the Planck satellite data on
the neutrino masses. In terms of the range of the scalar interaction mediated
over a distance of order $m^{-1}$, this leads to the small interval $4\,\mu m
\lesssim m^{-1} \lesssim 68\, \mu m$ within reach of future experimental tests
of deviations from Newton's gravitational inverse-square law. | Measurement of the Mass and Stellar Population Distribution in M82 with
the LBT: We present a K-band spectroscopic study of the stellar and gas kinematics,
mass distribution, and stellar populations of the archetypical starburst galaxy
M82. Our results are based on a single spectrum at a position angle of 67.5
degrees through the K-band nucleus. We used the CO stellar absorption band head
at 2.29 {\mu}m (CO_2.29) to measure the rotation curve out to nearly 4 kpc
radius on both the eastern and western sides of the galaxy. Our data show that
the rotation curve is flat from 1 - 4 kpc. This stands in sharp contrast to
some previous studies, which have interpreted H I and CO emission-line
position-velocity diagrams as evidence for a declining rotation curve. The
kinematics of the Br\gamma, H_2, and He I emission lines are consistent with,
although characterized by slightly higher velocities than, the stellar
kinematics. We derived M82's mass distribution from our stellar kinematic
measurements and estimate its total dynamical mass is ~10^10 Msun. We measured
the equivalent width of CO_2.29 (W_2.29) as a function of distance from the
center of the galaxy to investigate the spatial extent of the red supergiant
(RSG) population. The variation in W_2.29 with radius clearly shows that RSGs
dominate the light inside 500 pc radius. M82's superwind is likely launched
from this region, where we estimate the enclosed mass is <= 2 x 10^9 Msun. |
The Panchromatic Hubble Andromeda Treasury: The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going HST
Multicycle Treasury program to image ~1/3 of M31's star forming disk in 6
filters, from the UV to the NIR. The full survey will resolve the galaxy into
more than 100 million stars with projected radii from 0-20 kpc over a
contiguous 0.5 square degree area in 828 orbits, producing imaging in the F275W
and F336W filters with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and
F160W with WFC3/IR. The resulting wavelength coverage gives excellent
constraints on stellar temperature, bolometric luminosity, and extinction for
most spectral types. The photometry reaches SNR=4 at F275W=25.1, F336W=24.9,
F475W=27.9, F814W=27.1, F110W=25.5, and F160W=24.6 for single pointings in the
uncrowded outer disk; however, the optical and NIR data are crowding limited,
and the deepest reliable magnitudes are up to 5 magnitudes brighter in the
inner bulge. All pointings are dithered and produce Nyquist-sampled images in
F475W, F814W, and F160W. We describe the observing strategy, photometry,
astrometry, and data products, along with extensive tests of photometric
stability, crowding errors, spatially-dependent photometric biases, and
telescope pointing control. We report on initial fits to the structure of M31's
disk, derived from the density of RGB stars, in a way that is independent of
the assumed M/L and is robust to variations in dust extinction. These fits also
show that the 10 kpc ring is not just a region of enhanced recent star
formation, but is instead a dynamical structure containing a significant
overdensity of stars with ages >1 Gyr. (Abridged) | Peak statistics for the primordial black hole abundance: The primordial black hole (PBH) abundance evaluated by the conventional
Press-Schechter (PS) probability distribution is shown to be equivalent to the
high-peak limit of a special point-like peak statistics via unphysical
dimensionality reduction of the Bardeen-Bond-Kaiser-Szalay (BBKS) theory. The
fact that PBHs are formed at high peak values $\nu_c \gg 1$ leads to a
systematic bias proportional to $\nu_c^3$ between the predictions of the PS
method and the physical BBKS peak theory in a general three-dimensional spatial
configuration. As long as realistic PBHs are collapsed from three-dimensional
density peaks in space, the systematic bias led by $\nu_c^3$ implies a
significant underestimation of the PBH abundance reported by the PS method. For
the inflationary spectrum in the narrow-spike class, the underestimation in the
extended mass functions is further enlarged by at least a factor of $10^{2.5}$
in all mass range, indicating a severer constraint to models in the favor of
considering PBHs as all dark matter in a certain mass range. |
The pre-inflationary and inflationary fast-roll eras and their
signatures in the low CMB multipoles: We study the entire coupled evolution of the inflaton and the scale factor
for general initial conditions at a given initial time. The generic early
universe evolution has three stages: decelerated fast-roll followed by
inflationary fast roll and then inflationary slow-roll. This evolution is valid
for all regular inflaton potentials. In addition, we find a special (extreme)
slow-roll solution starting at t = -infty in which the fast-roll stages are
absent. At some time t = t_*, the generic evolution backwards in time reaches a
mathematical singu- larity where a(t) vanishes and Hubble becomes singular. We
find the general behaviour near the singularity. The classical inflaton
description is valid for t-t_* > 10 t_{Planck} well before the beginning of
inflation, quantum loop effects are negligible there. The singularity is never
reached in the validity region of the classical treatment and therefore it is
not a real physical phenomenon here. The whole evolution of the fluctuations is
computed. The Bunch-Davies initial conditions (BDic) are generalized for the
present case. The power spectrum gets dynamically modified by the effect of the
fast-roll eras and the BDic choice at a finite time through the transfer
function D(k) of initial conditions. D(0) = 0. D(k) presents a first peak for k
~ 2/eta_0 (eta_0 being the conformal initial time), then oscillates with
decreasing amplitude and vanishes asymptotically for k -> infty. The transfer
function D(k) affects the low CMB multipoles C_l: the change Delta C_l/C_l for
l=1-5 is computed as a function of the starting instant of the fluctuations
t_0. CMB quadrupole observations give large suppressions which are well
reproduced here(Abridged) | Cosmological parameter constraints using phenomenological symbolic
expressions: On the significance of symbolic expression complexity and
accuracy: Phenomenological models are widely used in cosmology in relation to
constraining different cosmological models, with two common examples being
cosmographic expansions and modeling the equation-of-state parameter of dark
energy. This work presents a study of how using different phenomenological
expressions for observables and physical quantities versus using physically
motivated, derived expressions affects cosmological parameter constraints. The
study includes the redshift-distance relation and Hubble parameter as
observables, and the dark energy equation-of-state parameter as a physical
quantity, and focuses on constraining the cosmological parameter
$\Omega_{\Lambda}$. The observables and equation-of-state parameter are all
modeled both using the physical, derived expressions and a variety of
phenomenological models with different levels of accuracy and complexity. The
results suggest that the complexity of phenomenological expressions only has
minor impact on the parameter constraints unless the complexity is very high.
The results also indicate that statistically significantly different results
can be expected from parameter constraints using different phenomenological
models if the models do not have very similar accuracy. This suggests that a
good practice is to use multiple phenomenological models when possible, in
order to assess the model dependence of results. Straightforward examples of
this is that results obtained using cosmographic expansions should always be
checked against similar results obtained with expansions of other order, and
when using phenomenological models such as for the equation-of-state
parameters, robustness of results could be assessed using fitted models from
symbolic regression, similar to what is done in this study. |
Cosmological bounds on dark matter-photon coupling: We investigate an extension of the $\Lambda$CDM model where the dark matter
(DM) is coupled to photons, inducing a nonconservation of the numbers of
particles for both species, where the DM particles are allowed to dilute
throughout the cosmic history with a small deviation from the standard
evolution decaying into photons, while the associated scattering processes are
assumed to be negligible. In addition, we consider the presence of massive
neutrinos with the effective number of species $N_{\rm eff}$ as a free
parameter. The effects of the DM-photon coupling on the cosmic microwave
background (CMB) and matter power spectra are analyzed. We derive the
observational constraints on the model parameters by using the data from CMB,
baryonic acoustic oscillation (BAO) measurements, the recently measured new
local value of the Hubble constant from the Hubble Space Telescope, and large
scale structure (LSS) information from the abundance of galaxy clusters. The
DM-photon coupling parameter $\Gamma_{\gamma }$ is constrained to
$\Gamma_{\gamma } \leq 1.3 \times10^{-5}$ (at 95\% C.L.) from the joint
analysis carried out by using all the mentioned data sets. The neutrino mass
scale $\sum m_{\nu}$ upper bounds at 95\% C.L. are obtained as $\sum m_{\nu}
\sim 0.9$ eV and $\sum m_{\nu} \sim 0.4$ eV with and without the LSS data,
respectively. We observe that the DM-photon coupling cause significant changes
in the best fit value of $N_{\rm eff}$ but yields statistical ranges of $N_{\rm
eff}$ compatible with the standard predictions, and we do not find any evidence
of dark radiation. Due to nonconservation of photons in our model, we also
evaluate and analyze the effects on the BAO acoustic scale at the drag epoch.
The DM-photon coupling model yields high values of Hubble constant consistent
with the local measurement, and thus alleviates the tension on this parameter. | Variable Stars in the Fornax dSph Galaxy. III. The Globular Cluster
Fornax 5: We present a new study of the variable star population in globular cluster 5
of the Fornax dwarf spheroidal galaxy, based on B and V time series photometry
obtained with the MagIC camera of the 6.5 m Magellan Clay telescope and
complementary HST archive data. Light curves and accurate periodicities were
obtained for 30 RR Lyrae stars and 1 SX Phoenicis variable. The RR Lyrae sample
includes 15 fundamental-mode pulsators, 13 first-overtone pulsators, 1
candidate double-mode pulsator and one RR Lyrae star with uncertain type
classification.
The average and minimum periods of the ab-type RR Lyrae stars, <Pab>=0.590
days, P(ab,min)=0.53297 days, and the position in the horizontal branch
type--metallicity plane, indicate that the cluster has Oosterhoff-intermediate
properties, basically confirming previous indications by Mackey & Gilmore
(2003b), although with some differences both in the period and type
classification of individual variables.
The average apparent magnitude of the Fornax 5 RR Lyrae stars is
<V(RR)>=21.35 +/- 0.02 mag (sigma=0.07 mag, average on 14 stars more likely
belonging to the cluster, and having well sampled light curves). This value
leads to a true distance modulus of mu0=20.76 +/- 0.07 (d=141.9 (+4.6;-4.5)
kpc) if we adopt for the cluster the metal abundance by Buonanno et al. (1998;
[Fe/H]=-2.20 +/- 0.20), or mu0=20.66 +/- 0.07 (d=135.5 (+4.4;-4.3) kpc), if we
adopt Strader et al.'s (2003) metal abundance ([Fe/H]=-1.73 +/- 0.13). |
The Evolution of Dusty Star formation in Galaxy Clusters to z = 1:
Spitzer IR Observations of the First Red-Sequence Cluster Survey: We present an IR study of high-redshift galaxy clusters with the MIPS camera
on the Spitzer Space Telescope. Employing a sample of 42 clusters from the
RCS-1 over the redshift range 0.3 < z < 1.0 and spanning an approximate range
in mass of 10^{14-15} Msun, we show the number of IR-luminous galaxies in
clusters above a fixed IR luminosity of 2x10^{11} Msun per unit cluster mass
evolves as (1+z)^{5.1+/-1.9}. These results assume a single star forming galaxy
template; the presence of AGN, and an evolution in their relative contribution
to the mid-IR galaxy emission, will alter the overall number counts per cluster
and their rate of evolution. We infer the total SFR per unit cluster mass and
find T_SFR/M_c ~ (1+z)^{5.4+/-1.9}. This evolution can be attributed entirely
to the change in the in-falling field galaxy population. The T_SFR/M_c (binned
over all redshift) decreases with increasing cluster mass with a slope
(T_SFR/M_c ~ M_c^{-1.5+/-0.4}) consistent with the dependence of the
stellar-to-total mass per unit cluster mass seen locally. The inferred star
formation seen here could produce ~5-10% of the total stellar mass in massive
clusters at z = 0. Finally, we show a clear decrease in the number of IR-bright
galaxies per unit optical galaxy in the cluster cores, confirming star
formation continues to avoid the highest density regions of the universe at z ~
0.75 (the average redshift of the high-redshift clusters). While several
previous studies appear to show enhanced star formation in high-redshift
clusters relative to the field we note that these papers have not accounted for
the overall increase in galaxy or dark matter density at the location of
clusters. Once this is done, clusters at z ~ 0.75 have the same or less star
formation per unit mass or galaxy as the field. | Universal structure of dark matter haloes over a mass range of 20 orders
of magnitude: Cosmological models in which dark matter consists of cold elementary
particles predict that the dark halo population should extend to masses many
orders of magnitude below those at which galaxies can form. Here we report a
cosmological simulation of the formation of present-day haloes over the full
range of observed halo masses (20 orders of magnitude) when dark matter is
assumed to be in the form of weakly interacting massive particles of mass
approximately 100 gigaelectronvolts. The simulation has a full dynamic range of
30 orders of magnitude in mass and resolves the internal structure of hundreds
of Earth-mass haloes in as much detail as it does for hundreds of rich galaxy
clusters. We find that halo density profiles are universal over the entire mass
range and are well described by simple two-parameter fitting formulae. Halo
mass and concentration are tightly related in a way that depends on cosmology
and on the nature of the dark matter. For a fixed mass, the concentration is
independent of the local environment for haloes less massive than those of
typical galaxies. Haloes over the mass range of 10^3 to 10^11 solar masses
contribute about equally (per logarithmic interval) to the luminosity produced
by dark matter annihilation, which we find to be smaller than all previous
estimates by factors ranging up to one thousand. |
The Effective Field Theory of Large-Scale Structure and Multi-tracer: We study the performance of the perturbative bias expansion when combined
with the multi-tracer technique, and their impact on the extraction of
cosmological parameters. We consider two populations of tracers of large-scale
structure and perform a series of Markov chain Monte Carlo analysis for those
two tracers separately. The constraints in $\omega_{\rm cdm}$ and $h$ using
multi-tracer are less biased and approximately $60\%$ better than those
obtained for a single tracer. The multi-tracer approach also provides stronger
constraints on the bias expansion parameters, breaking degeneracies between
them and with their error being typically half of the single-tracer case.
Finally, we studied the impacts caused in parameter extraction when including a
correlation between the stochastic field of distinct tracers. We also include a
study with galaxies showing that multi-tracer still lead to substantial gains
in the cosmological parameters. | Gravitational lenses in hydrodynamical simulations: The gravitational lensing signal produced by a galaxy or a galaxy cluster is
determined by its total matter distribution, providing us with a way to
directly constrain their dark matter content. State-of-the-art numerical
simulations successfully reproduce many observed properties of galaxies and can
be used as a source of mock observations and predictions. Many gravitational
lensing studies aim at constraining the nature of dark matter, discriminating
between cold dark matter and alternative models. However, many past results are
based on the comparison to simulations that did not include baryonic physics.
Here we show that the presence of baryons can significantly alter the
predictions: we look at the structural properties (profiles and shapes) of
elliptical galaxies and at the inner density slope of subhaloes. Our results
demonstrate that future simulations must model the interplay between baryons
and alternative dark matter, to generate realistic predictions that could
significantly modify the current constraints. |
Expanded Search for z~10 Galaxies from HUDF09, ERS, and CANDELS Data:
Evidence for Accelerated Evolution at z>8?: We search for z~10 galaxies over ~160 arcmin^2 of WFC3/IR data in the Chandra
Deep Field South, using the public HUDF09, ERS, and CANDELS surveys, that reach
to 5sigma depths ranging from 26.9 to 29.4 in H_160 AB mag. z>~9.5 galaxy
candidates are identified via J_125-H_160>1.2 colors and non-detections in any
band blueward of J_125. Spitzer IRAC photometry is key for separating the
genuine high-z candidates from intermediate redshift (z~2-4) galaxies with
evolved or heavily dust obscured stellar populations. After removing 16 sources
of intermediate brightness (H_160~24-26 mag) with strong IRAC detections, we
only find one plausible z~10 galaxy candidate in the whole data set, previously
reported in Bouwens et al. (2011). The newer data cover a 3x larger area and
provide much stronger constraints on the evolution of the UV luminosity
function (LF). If the evolution of the z~4-8 LFs is extrapolated to z~10, six
z~10 galaxies are expected in our data. The detection of only one source
suggests that the UV LF evolves at an accelerated rate before z~8. The
luminosity density is found to increase by more than an order of magnitude in
only 170 Myr from z~10 to z~8. This increase is >=4x larger than expected from
the lower redshift extrapolation of the UV LF. We are thus likely witnessing
the first rapid build-up of galaxies in the heart of cosmic reionization.
Future deep HST WFC3/IR data, reaching to well beyond 29 mag, can enable a more
robust quantification of the accelerated evolution around z~10. | Ultra deep sub-kpc view of nearby massive compact galaxies: Using Gemini North telescope ultra deep and high resolution (sub-kpc) K-band
adaptive optics imaging of a sample of 4 nearby (z~0.15) massive
(~10^{11}M_sun) compact (R<1.5 kpc) galaxies, we have explored the structural
properties of these rare objects with an unprecedented detail. Our surface
brightness profiles expand over 12 magnitudes in range allowing us to explore
the presence of any faint extended envelope on these objects down to stellar
mass densities ~10^{6} M_sun/kpc^{2} at radial distances of ~15 kpc. We find no
evidence for any extended faint tail altering the compactness of these
galaxies. Our objects are elongated, resembling visually S0 galaxies, and have
a central stellar mass density well above the stellar mass densities of objects
with similar stellar mass but normal size in the present universe. If these
massive compact objects will eventually transform into normal size galaxies,
the processes driving this size growth will have to migrate around
2-3x10^{10}M_sun stellar mass from their inner (R<1.7 kpc) region towards their
outskirts. Nearby massive compact galaxies share with high-z compact massive
galaxies not only their stellar mass, size and velocity dispersion but also the
shape of their profiles and the mean age of their stellar populations. This
makes these singular galaxies unique laboratories to explore the early stages
of the formation of massive galaxies. |
Optimizing simulation parameters for weak lensing analyses involving
non-Gaussian observables: We performed a series of numerical experiments to quantify the sensitivity of
the predictions for weak lensing statistics obtained in raytracing DM-only
simulations, to two hyper-parameters that influence the accuracy as well as the
computational cost of the predictions: the thickness of the lens planes used to
build past light-cones and the mass resolution of the underlying DM simulation.
The statistics considered are the power spectrum and a series of non-Gaussian
observables, including the one-point probability density function, lensing
peaks, and Minkowski functionals. Counter-intuitively, we find that using thin
lens planes ($< 60~h^{-1}$Mpc on a $240~h^{-1}$Mpc simulation box) suppresses
the power spectrum over a broad range of scales beyond what would be acceptable
for an LSST-type survey. A mass resolution of $7.2\times
10^{11}~h^{-1}\,M_{\odot}$ per DM particle (or 256$^3$ particles in a
($240~h^{-1}$Mpc)$^3$ box) is sufficient to extract information using the power
spectrum and non-Gaussian statistics from weak lensing data at angular scales
down to 1 arcmin with LSST-like levels of shape noise. | Stochastic Gravitational Wave Background from Neutron Star r-mode
Instability Revisited: We revisit the possibility and detectability of a stochastic gravitational
wave background (SGWB) produced by a cosmological population of newborn neutron
stars (NSs) with r-mode instabilities. We show that the resultant SGWB is
insensitive to the choice of CSFR models, but depends strongly on the evolving
behavior of CSFR at low redshifts. Our results show that the dimensionless
energy density $\Omega_{\rm{GW}}$ could have a peak amplitude of $\simeq
(1-3.5) \times10^{-8}$ in the frequency range $(200-1000)$~Hz. However, such a
high mode amplitude is unrealistic as it is known that the maximum value is
much smaller and at most $10^{-2}$. A realistic estimate of $\Omega_{\rm{GW}}$
should be at least 4 orders of magnitude lower ($\sim 10^{-12}$), which leads
to a pessimistic outlook for the detection of r-mode background. We consider
different pairs of terrestrial interferometers (IFOs) and compare two
approaches to combine multiple IFOs in order to evaluate the detectability of
this GW background. Constraints on the total emitted GW energy associated with
this mechanism to produce a detectable stochastic background are $\sim 10^{-3}
M_{\odot} c^2$ for two co-located advanced LIGO detectors, and $2 \times
10^{-5} M_{\odot} c^2$ for two Einstein Telescopes. These constraints may also
be applicable to alternative GW emission mechanisms related to oscillations or
instabilities in NSs depending on the frequency band where most GWs are
emitted. |
Neural physical engines for inferring the halo mass distribution
function: An ambitious goal in cosmology is to forward-model the observed distribution
of galaxies in the nearby Universe today from the initial conditions of
large-scale structures. For practical reasons, the spatial resolution at which
this can be done is necessarily limited. Consequently, one needs a mapping
between the density of dark matter averaged over ~Mpc scales, and the
distribution of dark matter halos (used as a proxy for galaxies) in the same
region. Here we demonstrate a method for determining the halo mass distribution
function by learning the tracer bias between density fields and halo catalogues
using a neural bias model. The method is based on the Bayesian analysis of
simple, physically motivated, neural network-like architectures, which we
denote as neural physical engines, and neural density estimation. As a result,
we are able to sample the initial phases of the dark matter density field
whilst inferring the parameters describing the halo mass distribution function,
providing a fully Bayesian interpretation of both the initial dark matter
density distribution and the neural bias model. We successfully run an upgraded
BORG inference using our new likelihood and neural bias model with halo
catalogues derived from full N-body simulations. We notice orders of magnitude
improvement in modelling compared to classical biasing techniques. | Inflation (2023): This is a review of the current status of studies of cosmological inflation,
extracted from Chapter 23 of the 2023 edition of the `Review of Particle
Physics': R.L. Workman et al. (Particle Data Group), Prog. Theor. Exp. Phys.,
2022, 083C01 (2022) and 2023 update. |
X-ray Temperatures, Luminosities, and Masses From XMM-Newton Follow-up
of the First Shear-selected Galaxy Cluster Sample: We continue the study of the first sample of shear-selected clusters (Wittman
et al. 2006) from the initial 8.6 square degrees of the Deep Lens Survey (DLS,
Wittman et al. 2002); a sample with well-defined selection criteria
corresponding to the highest ranked shear peaks in the survey area. We aim to
characterize the weak lensing selection by examining the sample's X-ray
properties. There are multiple X-ray clusters associated with nearly all the
shear peaks: 14 X-ray clusters corresponding to seven DLS shear peaks. An
additional three X-ray clusters cannot be definitively associated with shear
peaks, mainly due to large positional offsets between the X-ray centroid and
the shear peak. Here we report on the X-ray properties of the 17 X-ray
clusters. The X-ray clusters display a wide range of luminosities and
temperatures; the Lx-Tx relation we determine for the shear-associated X-ray
clusters is consistent with X-ray cluster samples selected without regard to
dynamical state, while it is inconsistent with self-similarity. For a subset of
the sample, we measure X-ray masses using temperature as a proxy, and compare
to weak lensing masses determined by the DLS team (Abate et al. 2009; Wittman
et al. 2014). The resulting mass comparison is consistent with equality. The
X-ray and weak lensing masses show considerable intrinsic scatter (~48%), which
is consistent with X-ray selected samples when their X-ray and weak lensing
masses are independently determined. | Micromegas micro-TPC for direct Dark Matter search with MIMAC: The MIMAC project is a multi-chamber detector for Dark Matter search, aiming
at measuring both track and ionization with a matrix of micromegas micro-TPC
filled with He3 and CF4. Recent experimental results on the first measurements
of the Helium quenching factor at low energy (1 keV recoil) are presented,
together with the first simulation of the track reconstruction. Recontruction
of track of alpha from Radon impurities is shown as a first proof of concept. |
Growth index of matter perturbations in running vacuum models: We derive for the first time the growth index of matter perturbations of the
FLRW flat cosmological models in which the vacuum energy depends on redshift. A
particularly well motivated model of this type is the so-called quantum field
vacuum, in which apart from a leading constant term $\Lambda_0$ there is also a
$H^{2}$-dependence in the functional form of vacuum, namely
$\Lambda(H)=\Lambda_{0}+3\nu (H^{2}-H^{2}_{0})$. Since $|\nu|\ll1$ this form
endows the vacuum energy of a mild dynamics which affects the evolution of the
main cosmological observables at the background and perturbation levels.
Specifically, at the perturbation level we find that the growth index of the
running vacuum cosmological model is $\gamma_{\Lambda_{H}} \approx
\frac{6+3\nu}{11-12\nu}$ and thus it nicely extends analytically the result of
the $\Lambda$CDM model, $\gamma_{\Lambda}\approx 6/11$. | Using measurements of the cosmic bulk flow to constrain $f(R)$ Gravity: As an alternative explanation for the cosmic acceleration, $f(R)$ theories of
gravity can predict an almost identical expansion history to standard
$\Lambda$CDM, yet make very different predictions for the growth of
cosmological structures. Measurements of the cosmic bulk flow provides a method
for determining the strength of gravity over the history of structure
formation. We use the modified gravity N-body code ECOSMOG to simulate dark
matter particles and make predictions for the bulk flow magnitude in both
$\Lambda$CDM and $f(R)$ gravity. With the peculiar velocities output by ECOSMOG
we determine the bulk flow at depths ranging from $20h^{-1}$Mpc to
$50h^{-1}$Mpc, following the redshift and sky distribution of the 2MASS
Tully-Fisher survey (2MTF). At each depth, we find that the $\Lambda$CDM and
$f_{R0} = 10^{-5}$ simulations produce bulk flow measurements that are
consistent with $\Lambda$CDM predictions and the 2MTF survey at a $1\sigma$
level. We also find that adopting an $f(R)$ strength of $f_{R0} = 10^{-3}$
predict a much larger value for the bulk flow, which disagree with $\Lambda$CDM
predictions at all depths considered. We conclude that $f_{R0}$ must be
constrained to a level no greater than $10^{-4}$ to agree with bulk flow
measurements. |
Validating Synthetic Galaxy Catalogs for Dark Energy Science in the LSST
Era: Large simulation efforts are required to provide synthetic galaxy catalogs
for ongoing and upcoming cosmology surveys. These extragalactic catalogs are
being used for many diverse purposes covering a wide range of scientific
topics. In order to be useful, they must offer realistically complex
information about the galaxies they contain. Hence, it is critical to implement
a rigorous validation procedure that ensures that the simulated galaxy
properties faithfully capture observations and delivers an assessment of the
level of realism attained by the catalog. We present here a suite of validation
tests that have been developed by the Rubin Observatory Legacy Survey of Space
and Time (LSST) Dark Energy Science Collaboration (DESC). We discuss how the
inclusion of each test is driven by the scientific targets for static
ground-based dark energy science and by the availability of suitable validation
data. The validation criteria that are used to assess the performance of a
catalog are flexible and depend on the science goals. We illustrate the utility
of this suite by showing examples for the validation of cosmoDC2, the
extragalactic catalog recently released for the LSST DESC second Data
Challenge. | Decay of multiple dark matter particles to dark radiation in different
epochs does not alleviate the Hubble tension: Decaying cold dark matter (CDM) has been considered as a mechanism to tackle
the tensions in the Hubble expansion rate and the clustering of matter.
However, polarization measurements of the cosmic microwave background (CMB)
severely constrain the fraction of dark matter decaying before recombination,
and lensing of the CMB anisotropies by large-scale structure set strong
constraints on dark matter decaying after recombination. Together, these
constraints make an explanation of the Hubble tension in terms of decaying dark
matter unlikely. In response to this situation, we investigate whether a dark
matter ensemble with CDM particles decaying into free streaming dark radiation
in different epochs can alleviate the problem. We find that it does not. |
Euclid preparation. XXVII. Covariance model validation for the 2-point
correlation function of galaxy clusters: Aims. We validate a semi-analytical model for the covariance of real-space
2-point correlation function of galaxy clusters. Methods. Using 1000 PINOCCHIO
light cones mimicking the expected Euclid sample of galaxy clusters, we
calibrate a simple model to accurately describe the clustering covariance.
Then, we use such a model to quantify the likelihood analysis response to
variations of the covariance, and investigate the impact of a
cosmology-dependent matrix at the level of statistics expected for the Euclid
survey of galaxy clusters. Results. We find that a Gaussian model with
Poissonian shot-noise does not correctly predict the covariance of the 2-point
correlation function of galaxy clusters. By introducing few additional
parameters fitted from simulations, the proposed model reproduces the numerical
covariance with 10 per cent accuracy, with differences of about 5 per cent on
the figure of merit of the cosmological parameters $\Omega_{\rm m}$ and
$\sigma_8$. Also, we find that the cosmology-dependence of the covariance adds
valuable information that is not contained in the mean value, significantly
improving the constraining power of cluster clustering. Finally, we find that
the cosmological figure of merit can be further improved by taking mass binning
into account. Our results have significant implications for the derivation of
cosmological constraints from the 2-point clustering statistics of the Euclid
survey of galaxy clusters. | Particle dark matter searches outside the Local Group: If dark matter (DM) is composed by particles which are non-gravitationally
coupled to ordinary matter, their annihilations or decays in cosmic structures
can result in detectable radiation. We show that the most powerful technique to
detect a particle DM signal outside the Local Group is to study the angular
cross-correlation of non-gravitational signals with low-redshift gravitational
probes. This method allows to enhance signal-to-noise from the regions of the
Universe where the DM-induced emission is preferentially generated. We
demonstrate the power of this approach by focusing on GeV-TeV DM and on the
recent cross-correlation analysis between the 2MASS galaxy catalogue and the
Fermi-LAT gamma-ray maps. We show that this technique is more sensitive than
other extragalactic gamma-ray probes, such as the energy spectrum and angular
autocorrelation of the extragalactic background, and emission from clusters of
galaxies. Intriguingly, we find that the measured cross-correlation can be well
fitted by a DM component, with thermal annihilation cross section and mass
between 10 and 100 GeV, depending on the small-scale DM properties and
gamma-ray production mechanism. This solicits further data collection and
dedicated analyses. |
The Cepheids of Centaurus A (NGC 5128) and Implications for H0: An analysis based on new OGLE observations reaffirms Ferrarese et al.
discovery of 5 Type II Cepheids in NGC 5128. The distance to that comparatively
unreddened population is d=3.8+-0.4(se) Mpc. The classical Cepheids in NGC 5128
are the most obscured in the extragalactic sample (n=30) surveyed, whereas
groups of Cepheids tied to several SNe host galaxies feature negative
reddenings. Adopting an anomalous extinction law for Cepheids in NGC 5128 owing
to observations of SN 1986G (Rv~2.4) is not favoured, granted SNe Ia may follow
small Rv. The distances to classical Cepheids in NGC 5128 exhibit a dependence
on colour and CCD chip, which may arise in part from photometric contamination.
Applying a colour cut to mitigate contamination yields d~3.5 Mpc (V-I<1.3),
while the entire sample's mean is d~3.1 Mpc. The distance was established via
the latest VI Galactic Wesenheit functions that include the 10 HST calibrators,
and which imply a shorter distance scale than Sandage et al.2004 by ~>10% at
P~25d. HST monitored classical Cepheids in NGC 5128, and the SNe hosts NGC 3021
& NGC 1309, follow a shallower VI Wesenheit slope than ground-based
calibrations of the Milky Way, LMC, NGC 6822, SMC, and IC 1613. The discrepancy
is unrelated to metallicity since the latter group share a common slope over a
sizeable abundance baseline (a=-3.34+-0.08,d[Fe/H]~1). A negligible distance
offset between OGLE Cepheids and RR Lyr variables in the LMC, SMC, and IC 1613
bolsters assertions that VI-based Wesenheit functions are relatively
insensitive to chemical abundance. In sum, a metallicity effect (VI) is not the
chief source of uncertainty associated with the Cepheid distance to NGC 5128 or
the establishment of Hubble's constant, but rather it may be the admittedly
challenging task of obtaining precise, commonly standardized, multiepoch,
multiband, comparatively uncontaminated extragalactic Cepheid photometry. | Creation of cosmic structure in the complex galaxy cluster merger Abell
2744: We present a detailed strong lensing, weak lensing and X-ray analysis of
Abell 2744 (z = 0.308), one of the most actively merging galaxy clusters known.
It appears to have unleashed `dark', `ghost', `bullet' and `stripped'
substructures, each ~10^14 solar masses. The phenomenology is complex and will
present a challenge for numerical simulations to reproduce. With new, multiband
HST imaging, we identify 34 strongly-lensed images of 11 galaxies around the
massive Southern `core'. Combining this with weak lensing data from HST, VLT
and Subaru, we produce the most detailed mass map of this cluster to date. We
also perform an independent analysis of archival Chandra X-ray imaging. Our
analyses support a recent claim that the Southern core and Northwestern
substructure are post-merger and exhibit morphology similar to the Bullet
Cluster viewed from an angle. From the separation between X-ray emitting gas
and lensing mass in the Southern core, we derive a new and independent
constraint on the self-interaction cross section of dark matter particles
sigma/m <~ 3 \pm 1 cm^2 g^-1. In the Northwestern substructure, the gas, dark
matter, and galaxy components have become separated by much larger distances.
Most curiously, the `ghost' clump (primarily gas) leads the `dark' clump
(primarily dark matter) by more than 150 kpc. We propose an enhanced
`ram-pressure slingshot' scenario which may have yielded this reversal of
components with such a large separation, but needs further confirmation by
follow-up observations and numerical simulations. A secondary merger involves a
second `bullet' clump in the North and an extremely `stripped' clump to the
West. The latter appears to exhibit the largest separation between dark matter
and X-ray emitting baryons detected to date in our sky. |
Segregation Effects According to the Evolutionary Stage of Galaxy Groups: We study segregation phenomena in 57 groups selected from the 2PIGG catalog
of galaxy groups. The sample corresponds to those systems located in areas of
at least 80% redshift coverage out to 10 times the radius of the groups. The
dynamical state of the galaxy systems was determined after studying their
velocity distributions. We have used the Anderson-Darling test to distinguish
relaxed and non-relaxed systems. This analysis indicates that 84% of groups
have galaxy velocities consistent with the normal distribution, while 16% of
them have more complex underlying distributions. Properties of the member
galaxies are investigated taking into account this classification. Our results
indicate that galaxies in Gaussian groups are significantly more evolved than
galaxies in non-relaxed systems out to distances of about 4R200, presenting
signficantly redder (B-R) color. We also find evidence that galaxies with M_R <
-21.5 in Gaussian groups are closer to the condition of energy equipartition. | Dark Energy: Dark energy is one of the mysteries of modern science. It is unlike any known
form of matter or energy and has been detected so far only by its gravitational
effect of repulsion. Owing to its effects being discernible only at very very
large distance scales, dark energy was only detected at the turn of the last
century when technology had advanced enough to observe a greater part of the
universe in finer detail. The aim of the report is to gain a better
understanding of the mysterious dark energy. To this end, both theoretical
methods and observational evidence are studied. Three lines of evidence,
namely, the redshift data of type Ia supernovae, estimates of the age of the
universe by various methods, and the anisotropies in the cosmic background
radiation, build the case for existence of dark energy. The supernova data
indicate that the expansion of the universe is accelerating. The ages of the
oldest star clusters in the universe indicate that the universe is older than
previously thought to be. The anisotropies in the cosmic microwave background
radiation suggest that the universe is globally spatially flat. If one agrees
that the dynamics of the geometry of the universe is dictated by its
energy-momentum content through Einstein's general theory of relativity, then
all these independent observations lead to the amazing conclusion that the
amount of energy in the universe that is presently accounted for by matter and
radiation is not enough to explain these phenomena. One of the best and
simplest explanations for dark energy is the cosmological constant. While it
does not answer all questions, it certainly does manage to explain the
observations. The following report examines in some detail the dark energy
problem and the candidacy of the cosmological constant as the right theory of
dark energy. |
Internal delensing of Planck CMB temperature and polarization: We present a first internal delensing of CMB maps, both in temperature and
polarization, using the public foreground-cleaned (SMICA) Planck 2015 maps.
After forming quadratic estimates of the lensing potential, we use the
corresponding displacement field to undo the lensing on the same data. We build
differences of the delensed spectra to the original data spectra specifically
to look for delensing signatures. After taking into account reconstruction
noise biases in the delensed spectra, we find an expected sharpening of the
power spectrum acoustic peaks with a delensing efficiency of $29\,\%$ ($TT$)
$25\,\%$ ($TE$) and $22\,\%$ ($EE$). The detection significance of the
delensing effects is very high in all spectra: $12\,\sigma$ in $EE$
polarization; $18\,\sigma$ in $TE$; and $20\,\sigma$ in $TT$. The null
hypothesis of no lensing in the maps is rejected at $26\,\sigma$. While direct
detection of the power in lensing $B$-modes themselves is not possible at high
significance at Planck noise levels, we do detect (at $4.5\,\sigma$ under the
null hypothesis) delensing effects in the $B$-mode map, with $7\,\%$ reduction
in lensing power. Our results provide a first demonstration of polarization
delensing, and generally of internal CMB delensing, and stand in agreement with
the baseline $\Lambda$CDM Planck 2015 cosmology expectations. | Probing clustering features around Cl 0024+17: I present a spatial analysis of the galaxy distribution around the cluster Cl
0024+17. The basic aim is to find the scales where galaxies present a
significant deviation from an inhomogeneous Poisson statistical process. Using
the generalization of the Ripley, Besag, and the pair correlation functions for
non-stationary point patterns, I estimate these transition scales for a set of
1,000 Monte Carlo realizations of the Cl 0024+17 field, corrected for
completeness up to the outskirts. The results point out the presence of at
least two physical scales in this field at 31.4 and 112.9 arcseconds. The
second one is statistically consistent with the dark matter ring radius (about
75 arcseconds) previously identified by Jee et al. (2007). However, morphology
and anisotropy tests point out that a clump at about 120 arcseconds NW from the
cluster center could be the responsible for the second transition scale. These
results do not indicate the existence of a galaxy counterpart of the dark
matter ring, but the methodology developed to study the galaxy field as a
spatial point pattern provides a good statistical evaluation of the physical
scales around the cluster. I briefly discuss the usefulness of this approach to
probe features in galaxy distribution and N-body dark matter simulation data. |
Limits on Primordial Black Holes from M87: Primordial black holes in the solar mass range are a possibly significant
component of dark matter. We show how an argument relating the deflection of
light by such black holes in the density spike likely to exist around the M87
supermassive black hole, combined with the high resolution observations of the
EHT collaboration, can lead to a strong limits on the primordial black hole
mass fraction in an astrophysically relevant mass range. The results depend on
the model assumed for the dark matter spike and suggest the interest of further
understanding of such spikes as well as further high resolution observations on
supermassive black holes. | Hubble tensions: a historical statistical analysis: Statistical analyses of the measurements of the Hubble-Lema\^itre constant
$H_0$ (163 measurements between 1976 and 2019) show that the statistical error
bars associated with the observed parameter measurements have been
underestimated -- or the systematic errors were not properly taken into account
-- in at least 15-20\% of the measurements. The fact that the underestimation
of error bars for $H_0$ is so common might explain the apparent discrepancy of
values, which is formally known today as the Hubble tension. Here we have
carried out a recalibration of the probabilities with this sample of
measurements. We find that $x\sigma $ deviation is indeed equivalent in a
normal distribution to $x_{\rm eq.}\sigma $s deviation in the frequency of
values, where $x_{\rm eq.}=0.83x^{0.62}$. Hence, a tension of 4.4$\sigma $,
estimated between the local Cepheid-supernova distance ladder and cosmic
microwave background (CMB) data, is indeed a 2.1$\sigma $ tension in equivalent
terms of a normal distribution of frequencies, with an associated probability
$P(>x_{\rm eq.})=0.036$ (1 in 28). This can be increased up to a equivalent
tension of 2.5$\sigma $ in the worst of the cases of claimed 6$\sigma $
tension, which may anyway happen as a random statistical fluctuation. |
Mirror magnetic field and its impact on dark matter distribution in
galaxies: We obtain the value of the mirror magnetic field during different stages of
cosmological evolution. We consider the magnetic field generation in the
radiation-dominated era and the post-recombination epoch. We also estimate its
galactic low-scale value in the process of dynamo amplification. We discuss a
possible effect of the mirror magnetic field on the mirror matter distribution
in a galaxy. The model can be generalized by assuming the existence of kinetic
mixing between ordinary and mirror particles. | A mature cluster with X-ray emission at z=2.07: We report evidence of a fully established galaxy cluster at z=2.07,
consisting of a ~20sigma overdensity of red, compact spheroidal galaxies
spatially coinciding with extended X-ray emission detected with XMM-Newton. We
use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to
estimate the redshift of the structure from a prominent z=2.07 spectroscopic
redshift spike of emission-line galaxies, concordant with the accurate 12-band
photometric redshifts of the red galaxies. Using NICMOS and Keck AO
observations, we find that the red galaxies have elliptical morphologies and
compact cores. While they do not form a tight red sequence, their colours are
consistent with that of a >1.3$~Gyr population observed at z~2.1. From an X-ray
luminosity of .2*10^43 erg s^-1 and the stellar mass content of the red galaxy
population, we estimate a halo mass of 5.3-8*10^13 Msun, comparable to the
nearby Virgo cluster. These properties imply that this structure could be the
most distant, mature cluster known to date and that X-ray luminous,
elliptical-dominated clusters are already forming at substantially earlier
epochs than previously known. |
Cosmological Constraints on DGP Braneworld Gravity with Brane Tension: We perform a Markov Chain Monte Carlo analysis of the self-accelerating and
normal branch of Dvali-Gabadadze-Porrati braneworld gravity. By adopting a
parameterized post-Friedmann description of gravity, we utilize all of the
cosmic microwave background data, including the largest scales, and its
correlation with galaxies in addition to the geometrical constraints from
supernovae distances and the Hubble constant. We find that on both branches
brane tension or a cosmological constant is required at high significance with
no evidence for the unique Dvali-Gabadadze-Porrati modifications. The
cross-over scale must therefore be substantially greater than the Hubble scale
H_0 r_c > 3 and 3.5 at the 95% CL with and without uncertainties from spatial
curvature. With spatial curvature, the limit from the normal branch is
substantially assisted by the galaxy cross-correlation which highlights its
importance in constraining infrared modifications to gravity. | Magnification Bias in Gravitational Arc Statistics: The statistics of gravitational arcs in galaxy clusters is a powerful probe
of cluster structure and may provide complementary cosmological constraints.
Despite recent progresses, discrepancies still remain among modelling and
observations of arc abundance, specially regarding the redshift distribution of
strong lensing clusters. Besides, fast "semi-analytic" methods still have to
incorporate the success obtained with simulations. In this paper we discuss the
contribution of the magnification in gravitational arc statistics. Although
lensing conserves surface brightness, the magnification increases the
signal-to-noise ratio of the arcs, enhancing their detectability. We present an
approach to include this and other observational effects in semi-analytic
calculations for arc statistics. The cross section for arc formation ({\sigma})
is computed through a semi-analytic method based on the ratio of the
eigenvalues of the magnification tensor. Using this approach we obtained the
scaling of {\sigma} with respect to the magnification, and other parameters,
allowing for a fast computation of the cross section. We apply this method to
evaluate the expected number of arcs per cluster using an elliptical
Navarro--Frenk--White matter distribution. Our results show that the
magnification has a strong effect on the arc abundance, enhancing the fraction
of arcs, moving the peak of the arc fraction to higher redshifts, and softening
its decrease at high redshifts. We argue that the effect of magnification
should be included in arc statistics modelling and that it could help to
reconcile arcs statistics predictions with the observational data. |
A Study of Gravitational Lens Chromaticity using Ground-based Narrow
Band Photometry: We present observations of wavelength-dependent flux ratios for four
gravitational lens systems (SDSS~J1650+4251, HE~0435$-$1223, FBQ 0951+2635, and
Q~0142$-$100) obtained with the Nordic Optical Telescope. The use of narrowband
photometry, as well as the excellent seeing conditions during the observations,
allows us to study their chromatic behavior. For SDSS~J1650+4251, we determine
the extinction curve of the dust in the $z_L=0.58$ lens galaxy and find that
the 2175 \AA \ feature is absent. In the case of HE~0435$-$1223, we clearly
detect chromatic microlensing. This allows us to estimate the
wavelength-dependent size of the accretion disk. We find an R-band disk size of
$r^{R}_s=13\pm5$ light days for a linear prior on $r^{R}_s$ and $r^{R}_s=7\pm6$
light days for a logarithmic prior. For a power-law size-wavelength scaling of
$r_s\propto\lambda^{p}$, we were able to constrain the value of the exponent to
$p=1.3\pm0.3$ for both $r^{R}_s$ priors, which is in agreement with the
temperature profiles of simple thin disk models ($p=4/3$). | Precision calculations of the cosmic shear power spectrum projection: We compute the spherical-sky weak-lensing power spectrum of the shear and
convergence. We discuss various approximations, such as flat-sky, and first-
and second- order Limber equations for the projection. We find that the impact
of adopting these approximations is negligible when constraining cosmological
parameters from current weak lensing surveys. This is demonstrated using data
from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). We find that
the reported tension with Planck Cosmic Microwave Background (CMB) temperature
anisotropy results cannot be alleviated.
For future large-scale surveys with unprecedented precision, we show that the
spherical second-order Limber approximation will provide sufficient accuracy.
In this case, the cosmic-shear power spectrum is shown to be in agreement with
the full projection at the sub-percent level for l > 3, with the corresponding
errors an order of magnitude below cosmic variance for all l. When computing
the two-point shear correlation function, we show that the flat-sky fast Hankel
transformation results in errors below two percent compared to the full
spherical transformation. In the spirit of reproducible research, our numerical
implementation of all approximations and the full projection are publicly
available within the package nicaea at
http://www.cosmostat.org/software/nicaea. |
CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields: The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble
Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy
clusters. CLASH observations are carried out in 16 bands from UV to NIR to
derive accurate and reliable estimates of photometric redshifts. We present the
CLASH photometric redshifts and study the photometric redshift accuracy of the
arcs in more detail for the case of MACS1206.2-0847. We use the publicly
available Le Phare and BPZ photometric redshift codes on 17 CLASH galaxy
clusters. Using Le Phare code for objects with StoN>=10, we reach a precision
of 3%(1+z) for the strong lensing arcs, which is reduced to 2.4%(1+z) after
removing outliers. For galaxies in the cluster field the corresponding values
are 4%(1+z) and 3%(1+z). Using mock galaxy catalogues, we show that 3%(1+z)
precision is what one would expect from the CLASH photometry when taking into
account extinction from dust, emission lines and the finite range of SEDs
included in the photo-z template library. We study photo-z results for
different aperture photometry and find that the SExtractor isophotal photometry
works best. Le Phare and BPZ give similar photo-z results for the strong
lensing arcs as well as galaxies of the cluster field. Results are improved
when optimizing the photometric aperture shape showing an optimal aperture size
around 1" radius giving results which are equivalent to isophotal photometry.
Tailored photometry of the arcs improve the photo-z results. | Signatures of non-gaussianity in the isocurvature modes of primordial
black hole dark matter: Primordial black holes (PBHs) are black holes which may have formed very
early on during the radiation dominated era in the early universe. We present
here a method by which the large scale perturbations in the density of
primordial black holes may be used to place tight constraints on
non-gaussianity if PBHs account for dark matter (DM). The presence of
local-type non-gaussianity is known to have a significant effect on the
abundance of primordial black holes, and modal coupling from the observed CMB
scale modes can significantly alter the number density of PBHs that form within
different regions of the universe, which appear as DM isocurvature modes. Using
the recent \emph{Planck} constraints on isocurvature perturbations, we show
that PBHs are excluded as DM candidates for even very small local-type
non-gaussianity, $|f_{NL}|\approx0.001$ and remarkably the constraint on
$g_{NL}$ is almost as strong. Even small non-gaussianity is excluded if DM is
composed of PBHs. If local non-Gaussianity is ever detected on CMB scales, the
constraints on the fraction of the universe collapsing into PBHs (which are
massive enough to have not yet evaporated) will become much tighter. |
A Refined Measurement of the Mean Transmitted Flux in the Ly-alpha
Forest over 2 < z < 5 Using Composite Quasar Spectra: We present new measurements of the mean transmitted flux in the Ly-alpha
forest over 2 < z < 5 made using 6065 quasar spectra from the Sloan Digital Sky
Survey DR7. We exploit the general lack of evolution in the mean quasar
continuum to avoid the bias introduced by continuum fitting over the Ly-alpha
forest at high redshifts, which has been the primary systematic uncertainty in
previous measurements of the mean Ly-alpha transmission. The individual spectra
are first combined into twenty-six composites with mean redshifts spanning 2.25
< z_comp < 5.08. The flux ratios of separate composites at the same rest
wavelength are then used, without continuum fitting, to infer the mean
transmitted flux, F(z), as a fraction of its value at z~2. Absolute values for
F(z) are found by scaling our relative values to measurements made from
high-resolution data by Faucher-Giguere et al. (2008) at z < 2.5, where
continuum uncertainties are minimal. We find that F(z) evolves smoothly with
redshift, with no evidence of a previously reported feature at z~3.2. This
trend is consistent with a gradual evolution of the ionization and thermal
state of the intergalactic medium over 2 < z < 5. Our results generally agree
with the most careful measurements to date made from high-resolution data, but
offer much greater precision and extend to higher redshifts. This work also
improves upon previous efforts using SDSS spectra by significantly reducing the
level of systematic error. | The Redshift-Space Cluster-Galaxy Cross-Correlation Function: I.
Modeling Galaxy Infall onto Millennium Simulation Clusters and SDSS Groups: The large scale infall of galaxies around massive clusters provides a
potentially powerful diagnostic of structure growth, dark energy, and
cosmological deviations from General Relativity. We develop and test a method
to recover galaxy infall kinematics (GIK) from measurements of the
redshift-space cluster-galaxy cross-correlation function \xi_{cg}(r_p,r_\pi).
Using galaxy and halo samples from the Millennium simulation, we calibrate an
analytic model of the galaxy kinematic profiles comprised of a virialized
component with an isotropic Gaussian velocity distribution and an infall
component described by a skewed 2D t-distribution with a characteristic infall
velocity v_r and separate radial and tangential dispersions. We show that
convolving the real-space cross-correlation function with this velocity
distribution accurately predicts the redshift-space \xi_{cg}, and we show that
measurements of \xi_{cg} can be inverted to recover the four distinct elements
of the GIK profiles. These in turn provide diagnostics of cluster mass
profiles, and we expect the characteristic infall velocity v_r(r) in particular
to be insensitive to galaxy formation physics that can affect velocity
dispersions within halos. As a proof of concept we measure \xi_{cg} for rich
galaxy groups in the Sloan Digital Sky Survey and recover GIK profiles for
groups in two bins of central galaxy stellar mass. The higher mass bin has a
v_r(r) curve very similar to that of 10^{14} Msun halos in the Millennium
simulation, and the recovered kinematics follow the expected trends with mass.
GIK modeling of cluster-galaxy cross-correlations can be a valuable complement
to stacked weak lensing analyses, allowing novel tests of modified gravity
theories that seek to explain cosmic acceleration. |
Fold Lens Flux Anomalies: A Geometric Approach: We develop a new approach for studying flux anomalies in quadruply-imaged
fold lens systems. We show that in the absence of substructure, microlensing,
or differential absorption, the expected flux ratios of a fold pair can be
tightly constrained using only geometric arguments. We apply this technique to
11 known quadruple lens systems in the radio and infrared, and compare our
estimates to the Monte Carlo based results of Keeton, Gaudi, and Petters. We
show that a robust estimate for a flux ratio from a smoothly varying potential
can be found, and at long wavelengths those lenses deviating from from this
ratio almost certainly contain significant substructure. | Chemical abundances in the polar disk of NGC4650A: implications for cold
accretion scenario: The aim of the present study is to test whether the cold accretion of gas
through a "cosmic filament" Macci\`o et al. 2006 is a possible formation
scenario for the polar disk galaxy NGC 4650A. If polar disks form from cold
accretion of gas, the abundances of the HII regions may be similar to those of
very late-type spiral galaxies, regardless of the presence of a bright central
stellar spheroid, with total luminosity of few 10^9 Lsun. We use deep long slit
spectra obtained with the FORS2 spectrograph at the VLT in the optical and
near-infrared wavelength ranges for the brightest HII regions in the disk polar
disk of NGC 4650A. The strongest emission lines ([OII] Hbeta, [OIII], Halpha)
were used to derived oxygen abundances, metallicities and the global star
formation rates for the disk. The deep spectra available allowed us to measure
the Oxygen abundances (12 + log (O/H)) using the "Empirical method" based on
intensities of the strongest emission lines, and the "Direct method", based on
the determination of the electron temperature from the detection of weak
auroral lines, as the [OIII] at 4363 Angstrom. The Oxygen abundance measured
for the polar disk is then compared with those measured for different galaxy
types of similar total luminosities, and then compared against the predictions
of different polar ring formation scenarios. The average metallicity values for
the polar disk in NGC 4650A is Z=0.2 Zsun, and it is lower that the values
measured for ordinary spirals of similar luminosity. Moreover the gradient of
the metallicity is flat along the polar disk major axis, which implies none or
negligible metal enrichment from the stars in the older central spheroid. The
low metallicity value in the polar disk NGC 4650A and the flat metallicity
gradient are both consistent with a later infall of metal-poor gas, as expected
in the cold accretion processes. |
Predicting the Sufficient-Statistics Power Spectrum for Galaxy Surveys:
A Recipe for $P_{A*}(k)$: Future galaxy surveys hope to realize significantly tighter constraints on
various cosmological parameters. The higher number densities achieved by these
surveys will allow them to probe the smaller scales affected by non-linear
clustering. However, in these regimes, the standard power spectrum can extract
only a portion of such surveys' cosmological information. In contrast, the
alternate statistic $A^*$ has the potential to double these surveys'
information return, provided one can predict the $A^*$-power spectrum for a
given cosmology. Thus, in this work we provide a prescription for this power
spectrum $P_{A^*}(k)$, finding that the prescription is typically accurate to
about 5 per cent for near-concordance cosmologies. This prescription will thus
allow us to multiply the information gained from surveys such as Euclid and
WFIRST. | Precision cosmology with voids: definition, methods, dynamics: We propose a new definition of cosmic voids based on methods of Lagrangian
orbit reconstruction as well as an algorithm to find them in actual data called
DIVA. Our technique is intended to yield results which can be modeled
sufficiently accurately to create a new probe of precision cosmology. We then
develop an analytical model of the ellipticity of voids found by our method
based on Zel'dovich approximation. We measure in N-body simulation that this
model is precise at the 0.1% level for the mean ellipticity of voids of size
greater than ~4 Mpc/h. We estimate that at this scale, we are able to predict
the ellipticity with an accuracy of 0.02. Finally, we compare the distribution
of void shapes in N-body simulation for two different equations of state w of
the dark energy. We conclude that our method is far more accurate than Eulerian
methods and is therefore promising as a precision probe of dark energy
phenomenology. |
Massive starburst galaxies in a z=2.16 proto-cluster unveiled by
panoramic H-alpha mapping: We present a panoramic narrow-band study of H-alpha emitters in the field of
the z=2.16 proto-cluster around PKS1138-262 using MOIRCS on the Subaru
Telescope. We find 83 H-alpha emitters down to a SFR(Ha)~10Msun/yr across a
~7'x7' region centered on the radio galaxy, and identify ~10-Mpc scale
filaments of emitters running across this region. By examining the properties
of H-alpha emitters within the large-scale structure, we find that galaxies in
the higher-density environments at z=2.16 tend to have redder colours and
higher stellar masses compared to galaxies in more underdense regions. We also
find a population of H-alpha emitters with red colours ((J-Ks)>1), which are
much more frequent in the denser environments and which have apparently very
high stellar masses with M*>~10^11Msun, implying that these cluster galaxies
have already formed a large part of their stellar mass before z~2. Spitzer
Space Telescope 24-micron data suggests that many of these red H-alpha emitters
are bright, dusty starbursts (rather than quiescent sources). We also find that
the proto-cluster galaxies follow the same correlation between SFR and M* (the
"main sequence") of z~2 field star-forming galaxies, but with an excess of
massive galaxies. These very massive star-forming galaxies are not seen in our
similar, previous study of z~1 clusters, suggesting that their star-formation
activity has been shut off at 1<~z<~2. We infer that the massive red (but
active) galaxies in this rich proto-cluster are likely to be the products of
environmental effects, and they represent the accelerated galaxy formation and
evolution in a biased high density region in the early Universe. | Analyzing clustering of astrophysical gravitational-wave sources:
Luminosity-distance space distortions: We present a formulation of observed number density fluctuations of
gravitational-wave (GW) sources in a three dimensional space. In GW
observations, redshift identification for each GW source is a challenging
issue, in particular, for high redshift sources. The use of observed luminosity
distance as a distance indicator will be a simple yet optimal way for measuring
the clustering signal. We derive the density fluctuations of GW sources
estimated from observed luminosity distance and sky position of each source.
The density fluctuations are distorted as similar to the so-called redshift
space distortions in galaxy surveys but with several differences. We then show
the two-point correlation function and multipole power spectrum in the presence
of the distortion effect. We find that the line-of-sight derivative of the
lensing convergence, which does not appear in the redshift-space distortions,
leads to significant distortions in the observed correlation function. In
addition, the lensing effect affects higher-order multipole power spectra and
its signal-to-noise at high redshifts. |
On the Possible Enhancement of the Global $21$-cm Signal at Reionization
from the Decay of Cosmic String Cusps: We consider cosmic string cusp annihilations as a possible source of
enhancement to the global background radiation temperature in $21$-cm photons
at reionization. A soft photon spectrum is induced via the Bremsstrahlung and
Synchrotron emission of electrons borne out of QCD jets formed off the cusp.
The maximal energy density background comes from synchrotron induced photons
with a string tension of $G\mu \sim 10^{-18}$. In this instance, the radiation
background at reionization is heated up by $5\cdot 10^{-3} \,\, K$. We find
that the depth of the absorption trough ($\delta T_b$) in $21$-cm at
reionization is altered by one part in $10^4$ from the strings, requiring high
precision measurements to be detectable. This mechanism cannot explain the
$\delta T_b$ observed by the EDGES experiment. | Measuring cavity powers of active galactic nuclei in clusters using a
hybrid X-ray-radio method -- A new window on feedback opened by subarcsecond
LOFAR-VLBI observations: Measurements of the quantity of radio-mode feedback injected by an active
galactic nucleus into the cluster environment have mostly relied on X-ray
observations, which reveal cavities in the intracluster medium excavated by the
radio lobes. However, the sensitivity required to accurately constrain the
dimensions of these cavities has proven to be a major limiting factor and is
the main bottleneck on high-redshift measurements. We describe a hybrid method
based on a combination of X-ray and radio observations, which aims to enhance
our ability to study radio-mode feedback. In this paper, we present one of the
first samples of galaxy clusters observed with the International LOFAR
Telescope (ILT) at 144 MHz and use this sample to test the hybrid method at
lower frequencies than before. By comparing our measurements with results found
in literature based on the traditional method using only X-ray observations, we
find that the hybrid method provides consistent results to the traditional
method. In addition, we find that the correlation between the traditional
method and the hybrid method improves as the X-ray cavities are more clearly
defined. This suggests that using radio lobes as proxies for cavities may help
to circumvent systematic uncertainties in the cavity volume measurements.
Encouraged by the high volume of unique ILT observations successfully
processed, this hybrid method enables radio-mode feedback to be studied at high
redshifts for the first time even for large samples of clusters. |
An Interacting Galaxy System Along a Filament in a Void: Cosmological voids provide a unique environment for the study of galaxy
formation and evolution. The galaxy population in their interior have
significantly different properties than average field galaxies. As part of our
Void Galaxy Survey (VGS), we have found a system of three interacting galaxies
(VGS_31) inside a large void. VGS_31 is a small elongated group whose members
are embedded in a common HI envelope. The HI picture suggests a filamentary
structure with accretion of intergalactic cold gas from the filament onto the
galaxies. We present deep optical and narrow band H_alpha data, optical
spectroscopy, near-UV and far-UV GALEX and CO(1-0) data. We find that one of
the galaxies, a Markarian object, has a ring-like structure and a tail evident
both in optical and HI. While all three galaxies form stars in their central
parts, the tail and the ring of the Markarian object are devoid of star
formation. We discuss these findings in terms of a gravitational interaction
and ongoing growth of galaxies out of a filament. VGS_31 is one of the first
observed examples of a filamentary structure in a void. It is an important
prototype for understanding the formation of substructure in a void. This
system also shows that the galaxy evolution in voids can be as dynamic as in
high density environments. | Generalised Fisher Matrices: The Fisher Information Matrix formalism is extended to cases where the data
is divided into two parts (X,Y), where the expectation value of Y depends on X
according to some theoretical model, and X and Y both have errors with
arbitrary covariance. In the simplest case, (X,Y) represent data pairs of
abscissa and ordinate, in which case the analysis deals with the case of data
pairs with errors in both coordinates, but X can be any measured quantities on
which Y depends. The analysis applies for arbitrary covariance, provided all
errors are gaussian, and provided the errors in X are small, both in comparison
with the scale over which the expected signal Y changes, and with the width of
the prior distribution. This generalises the Fisher Matrix approach, which
normally only considers errors in the `ordinate' Y. In this work, we include
errors in X by marginalising over latent variables, effectively employing a
Bayesian hierarchical model, and deriving the Fisher Matrix for this more
general case. The methods here also extend to likelihood surfaces which are not
gaussian in the parameter space, and so techniques such as DALI (Derivative
Approximation for Likelihoods) can be generalised straightforwardly to include
arbitrary gaussian data error covariances. For simple mock data and theoretical
models, we compare to Markov Chain Monte Carlo experiments, illustrating the
method with cosmological supernova data. We also include the new method in the
Fisher4Cast software. |
On the Probability Distributions of Ellipticity: In this paper we derive an exact full expression for the 2D probability
distribution of the ellipticity of an object measured from data, only assuming
Gaussian noise in pixel values. This is a generalisation of the probability
distribution for the ratio of single random variables, that is well-known, to
the multivariate case. This expression is derived within the context of the
measurement of weak gravitational lensing from noisy galaxy images. We find
that the third flattening, or epsilon-ellipticity, has a biased maximum
likelihood but an unbiased mean; and that the third eccentricity, or normalised
polarisation chi, has both a biased maximum likelihood and a biased mean. The
very fact that the bias in the ellipticity is itself a function of the
ellipticity requires an accurate knowledge of the intrinsic ellipticity
distribution of the galaxies in order to properly calibrate shear measurements.
We use this expression to explore strategies for calibration of biases caused
by measurement processes in weak gravitational lensing. We find that upcoming
weak lensing surveys like KiDS or DES require calibration fields of order of
several square degrees and 1.2 magnitude deeper than the wide survey in order
to correct for the noise bias. Future surveys like Euclid will require
calibration fields of order 40 square degree and several magnitude deeper than
the wide survey. We also investigate the use of the Stokes parameters to
estimate the shear as an alternative to the ellipticity. We find that they can
provide unbiased shear estimates at the cost of a very large variance in the
measurement. The python code used to compute the distributions presented in the
paper and to perform the numerical calculations are available on request. | Primordial non-Gaussianity from the large scale structure: Primordial non-Gaussianity is a potentially powerful discriminant of the
physical mechanisms that generated the cosmological fluctuations observed
today. Any detection of non-Gaussianity would have profound implications for
our understanding of cosmic structure formation. In this paper, we review past
and current efforts in the search for primordial non-Gaussianity in the large
scale structure of the Universe. |
Universal Profiles of the Intracluster Medium from Suzaku X-Ray and
Subaru Weak Lensing Obesrvations: We conduct a joint X-ray and weak-lensing study of four relaxed galaxy
clusters (Hydra A, A478, A1689 and A1835) observed by both Suzaku and Subaru
out to virial radii, with an aim to understand recently-discovered unexpected
feature of the ICM in cluster outskirts. We show that the average
hydrostatic-to-lensing total mass ratio for the four clusters decreases from
\sim 70% to \sim 40% as the overdensity contrast decreases from 500 to the
virial value.The average gas mass fraction from lensing total mass estimates
increases with cluster radius and agrees with the cosmic mean baryon fraction
within the virial radius, whereas the X-ray-based gas fraction considerably
exceeds the cosmic values due to underestimation of the hydrostatic mass. We
also develop a new advanced method for determining normalized cluster radial
profiles for multiple X-ray observables by simultaneously taking into account
both their radial dependence and multivariate scaling relations with
weak-lensing masses. Although the four clusters span a range of halo mass,
concentration, X-ray luminosity and redshift, we find that the gas entropy,
pressure, temperature and density profiles are all remarkably self-similar when
scaled with the lensing M_200 mass and r_200 radius.The entropy monotonically
increases out to \sim 0.5r_200 following the accretion shock heating model
K(r)\propto r^1.1, and flattens at \simgt 0.5r_200.The universality of the
scaled entropy profiles indicates that the thermalization mechanism over the
entire cluster region (>0.1r_200) is controlled by gravitation in a common to
all clusters, although the heating efficiency in the outskirts needs to be
modified from the standard law.The bivariate scaling functions of the gas
density and temperature reveal that the flattening of the outskirts entropy
profile is caused by the steepening of the temperature, rather than the
flattening of the gas density. | Large Scale Anisotropic Bias from Primordial non-Gaussianity: In this work we study the large scale structure bias in models of anisotropic
inflation. We use the Peak Background Splitting method in Excursion Set Theory
to find the scale-dependent bias. We show that the amplitude of the bias is
modified by a direction- dependent factor. In the specific anisotropic
inflation model which we study, the scale- dependent bias vanishes at leading
order when the long wavelength mode in squeezed limit is aligned with the
anisotropic direction in the sky. We also extend the scale-dependent bias
formulation to the general situations with primordial anisotropy. We find some
selection rules indicating that some specific parts of a generic anisotropic
bispectrum is picked up by the bias parameter. We argue that the anisotropic
bias is mainly sourced by the angle between the anisotropic direction and the
long wavelength mode in the squeezed limit. |
On the possibility of Baryon Acoustic Oscillation measurements at
redshift $z>7.6$ with the Roman Space Telescope: The Nancy Grace Roman Space Telescope (RST), with its field of view and high
sensitivity will make surveys of cosmological large-scale structure possible at
high redshifts. We investigate the possibility of detecting Baryon Acoustic
Oscillations (BAO) at redshifts $z>7.6$ for use as a standard ruler. We use
data from the hydrodynamic simulation \textsc{BlueTides} in conjunction with
the gigaparsec-scale Outer Rim simulation and a model for patchy reionization
to create mock RST High Latitude Survey grism data for Lyman-alpha emission
line selected galaxies at redshifts $z=7.4$ to $z=10$, covering 2280 square
degrees. We measure the monopoles of galaxies in the mock catalogues and fit
the BAO features. We find that for a line flux of $L = 7\times 10^{-17} \ {\rm
erg/s/cm}^{2}$, the $5 \sigma$ detection limit for the current design, the BAO
feature is partially detectable (measured in three out of four survey quadrants
analysed independently). The resulting root mean square error on the angular
diameter distance to $z=7.7$ is 7.9$\%$. If we improve the detection
sensitivity by a factor of two (i.e. $L = 3.5\times 10^{-17} \ {\rm
erg/s/cm}^{2}$), the distance error reduces to $1.4\%$. We caution that many
more factors are yet to be modelled, including dust obscuration, the damping
wing due to the intergalactic medium, and low redshift interlopers. If these
issues do not strongly affect the results, or different observational
techniques (such as use of multiple lines) can mitigate them, RST or similar
instruments may be able to constrain the angular diameter distance to the high
redshift Universe. | Australia Telescope Compact Array observations of Fermi unassociated
sources: We report results of the first phase of observations with the Australia
Telescope Compact Array (ATCA) at 5 and 9 GHz of the fields around 411
gamma-ray sources with declinations < +10 deg detected by Fermi but marked as
unassociated in the 2FGL catalogue. We have detected 424 sources with flux
densities in a range of 2 mJy to 6 Jy that lie within the 99 per cent
localisation uncertainty of 283 gamma-ray sources. Of these, 146 objects were
detected in both the 5 and 9 GHz bands. We found 84 sources in our sample with
a spectral index flatter than -0.5. The majority of detected sources are weaker
than 100 mJy and for this reason were not found in previous surveys.
Approximately 1/3 of our sample, 128 objects, have the probability of being
associated by more than 10 times than the probability of being a background
source found in the vicinity of a gamma-ray object by chance. We present the
catalogue of positions of these sources, estimates of their flux densities and
spectral indices where available. |
Submillimeter Array Identification of the Millimeter-Selected Galaxy
SSA22-AzTEC1: A Protoquasar in a Protocluster?: We present results from Submillimeter Array (SMA) 860-micron sub-arcsec
astrometry and multiwavelength observations of the brightest millimeter
(S_1.1mm = 8.4 mJy) source, SSA22-AzTEC1, found near the core of the SSA22
protocluster that is traced by Ly\alpha emitting galaxies at z = 3.09. We
identify a 860-micron counterpart with a flux density of S_860um = 12.2 +/- 2.3
mJy and absolute positional accuracy that is better than 0.3". At the SMA
position, we find radio to mid-infrared counterparts, whilst no object is found
in Subaru optical and near-infrared deep images at wavelengths \le 1 micron (J
> 25.4 in AB, 2\sigma). The photometric redshift estimate, using flux densities
at \ge 24 microns, indicates z_phot = 3.19^{+0.26}_{-0.35}, consistent with the
protocluster redshift. We then model the near-to-mid-infrared spectral energy
distribution (SED) of SSA22-AzTEC1, and find that the SED modeling requires a
large extinction (A_V \approx 3.4 mag) of starlight from a stellar component
with M_star ~ 10^{10.9} M_sun, assuming z = 3.1. Additionally, we find a
significant X-ray counterpart with a very hard spectrum (Gamma_eff = -0.34
^{+0.57}_{-0.61}), strongly suggesting that SSA22-AzTEC1 harbors a luminous AGN
(L_X ~ 3*10^{44} ergs s^{-1}) behind a large hydrogen column (N_H ~ 10^{24}
cm^{-2}). The AGN, however, is responsible for only ~10% of the bolometric
luminosity of the host galaxy, and therefore the star-formation activity likely
dominates the submillimeter emission. It is possible that SSA22-AzTEC1 is the
first example of a protoquasar growing at the bottom of the gravitational
potential underlying the SSA22 protocluster. | Uncorrelated Compensated Isocurvature Perturbations from kSZ Tomography: Compensated isocurvature perturbations (CIPs) are relative density
perturbations in which a baryon-density fluctuation is accompanied by a dark
matter density fluctuation such that the total-matter density is unperturbed.
These fluctuations can be produced primordially if multiple fields are present
during inflation, and therefore they can be used to differentiate between
different models for the early Universe. Kinetic Sunyaev-Zeldovich (kSZ)
tomography allows for the reconstruction of the radial-velocity field of matter
as a function of redshift. This technique can be used to reconstruct the
total-matter-overdensity field, independent of the galaxy-density field
obtained from large-scale galaxy surveys. We leverage the ability to measure
the galaxy- and matter-overdensity fields independently to construct a
minimum-variance estimator for the primordial CIP amplitude, based on a
mode-by-mode comparison of the two measurements. We forecast that a
configuration corresponding to CMB-S4 and VRO will be able to detect (at
$2\sigma$) a CIP amplitude $A$ (for a scale-invariant power spectrum) as small
as $A\simeq 5\times 10^{-9}$. Similarly, a configuration corresponding to SO
and DESI will be sensitive to a CIP amplitude $A\simeq 1\times 10^{-7}$. These
values are to be compared to current constraints $A \leq {\cal O}(0.01)$. |
SUBARU Spectroscopy of the Globular Clusters in the Virgo Giant
Elliptical Galaxy M86: We present the first spectroscopic study of the globular clusters (GCs) in
the giant elliptical galaxy (gE) M86 in the Virgo cluster. Using spectra
obtained in the Multi-Object Spectroscopy (MOS) mode of the Faint Object Camera
and Spectrograph (FOCAS) on the Subaru telescope, we measure the radial
velocities for 25 GCs in M86. The mean velocity of the GCs is derived to be vp
= -354+81 -79 km/s, which is different from the velocity of the M86 nucleus
(vgal = -234\pm41 km/s). We estimate the velocity dispersion of the GCs,
{\sigma}p = 292+32-32 km/s, and find a hint of rotation of the M86 GC system. A
comparison of the observed velocity dispersion profiles of the GCs and stars
with a prediction based on the stellar mass profile strongly suggests the
existence of an extended dark matter halo in M86. We also estimate the
metallicities and ages for 16 and 8 GCs, respectively. The metallicities of M86
GCs are in the range -2.0 < [Fe/H] < -0.2 with a mean value of -1.13\pm0.47.
These GCs show a wide age distribution from 4 to 15 Gyr. | The optical variability of flat-spectrum radio quasars in the SDSS
stripe 82 region: Context. Although a bluer-when-brighter trend is commonly observed in
blazars, the opposite trend of redder-when-brighter has also been found in some
blazars. Aims. We investigate the frequency of the redder-when-brighter trend
in flat-spectrum radio quasars (FSRQs). Methods. We investigate the optical
variability of 29 FSRQs in the SDSS Stripe 82 region using SDSS DR7 released
multi-epoch data covering about nine years. We determined the spectral index by
fitting a powerlaw to SDSS ugriz photometric data, and explored the
relationship between the spectral index and source brightness. Results. For all
FSRQs studied, we detect variations in r band flux of overall amplitude between
0.24 mag and 3.46 mag in different sources. Fourteen of 29 FSRQs display a
bluer-when-brighter trend. However, only one source exhibits a
redder-when-brighter trend, which implies that this behavior is rare in our
FSRQ sample. In this source, the thermal emission from the accretion disk may
be responsible for the redder-when-brighter trend. |
The Excursion set approach: Stratonovich approximation and Cholesky
decomposition: The excursion set approach is a framework for estimating how the number
density of nonlinear structures in the cosmic web depends on the expansion
history of the universe and the nature of gravity. A key part of the approach
is the estimation of the first crossing distribution of a suitably chosen
barrier by random walks having correlated steps: The shape of the barrier is
determined by the physics of nonlinear collapse, and the correlations between
steps by the nature of the initial density fluctuation field. We describe
analytic and numerical methods for calculating such first up-crossing
distributions. While the exact solution can be written formally as an infinite
series, we show how to approximate it efficiently using the Stratonovich
approximation. We demonstrate its accuracy using Monte-Carlo realizations of
the walks, which we generate using a novel Cholesky-decomposition based
algorithm, which is significantly faster than the algorithm that is currently
in the literature. | A simple parametrisation for coupled dark energy: As an alternative to the popular parametrisations of the dark energy equation
of state, we construct a quintessence model where the scalar field has a linear
dependence on the number of e-folds. Constraints on more complex models are
typically limited by the degeneracies that increase with the number of
parameters. The proposed parametrisation conveniently constrains the evolution
of the dark energy equation of state as it allows for a wide variety of time
evolutions. We also consider a non-minimal coupling to cold dark matter. We fit
the model with Planck and KiDS observational data. The CMB favours a
non-vanishing coupling with energy transfer from dark energy to dark matter.
Conversely, gravitational weak lensing measurements slightly favour energy
transfer from dark matter to dark energy, with a substantial departure of the
dark energy equation of state from -1. |
Primordial Black Holes Place the Universe in Stasis: A variety of scenarios for early-universe cosmology give rise to a population
of primordial black holes (PBHs) with a broad spectrum of masses. The
evaporation of PBHs in such scenarios has the potential to place the universe
into an extended period of "stasis" during which the abundances of matter and
radiation remain absolutely constant despite cosmological expansion. This
surprising phenomenon can give rise to new possibilities for early-universe
dynamics and lead to distinctive signatures of the evaporation of such PBHs. In
this paper, we discuss how this stasis epoch arises and explore a number of its
phenomenological consequences, including implications for inflationary
observables, the stochastic gravitational-wave background, baryogenesis, and
the production of dark matter and dark radiation. | A Note on the Abundance of Primordial Black Holes: Use and Misuse of the
Metric Curvature Perturbation: The formation of Primordial Black Holes (PBHs) through the collapse of large
fluctuations in the early universe is a rare event. This manifests itself, for
instance, through the non-Gaussian tail of the formation probability. To
compute such probability and the abundance of PBHs, the curvature perturbation
is frequently adopted. In this note we emphasize that its use does not provide
the correct PBH formation probability. Through a path-integral approach we show
that the exact calculation of the PBH abundance demands the knowledge of
multivariate joint probabilities of the curvature perturbation or,
equivalently, of all the corresponding connected correlators. |
Dynamics of the galactic component of Abell S1063 and MACS
J1206.2$-$0847: The galactic component in clusters is commonly thought to be generally
nonrotating and in a dynamical state different from that of a collisionally
relaxed system. In practice, a test of such a picture is often not available.
We consider the member galaxies of two clusters, Abell S1063 and MACS
J1206.2$-$0847, and study the possible presence of mean rotation and some
properties of their distribution in phase space. We look for empirical evidence
of factors normally found in collisionally relaxed systems and others
characteristic of violently-relaxed collisionless systems. Starting from the
CLASH-VLT data, we obtain positions, stellar masses, and individual
line-of-sight velocities for a large number of galaxies (N_{AS1063}=1200 and
N_{M1206}=650) extending out to 1.6 (Abell) and 2.5 (MACS) times the radius
r_{200}. We study the spatial distribution of the galaxy velocities and the
properties of the available galaxy sets when divided in stellar mass bins. To
test the presence of velocity dispersion anisotropy we compare the results
based on the Jeans equations with those obtained by assuming a specific form of
the galaxy distribution function incorporating the picture of violent
relaxation, where the total gravitational potential is imposed as set by the
available gravitational lensing observations. We find evidence of systematic
rotation in both clusters, with significant rotation in each core (within 0.5'
from the center) and no signatures of rotation at large radii. While no signs
are found of energy equipartition, there is a clear indication of (stellar)
mass segregation. Velocity dispersion anisotropy is present and qualitatively
similar to that found in violently relaxed collisionless systems; this last
conclusion is strengthened by the overall success in matching the observations
with the predictions of the physically justified distribution function. | The environmental dependence of the red galaxy sequence: The dependence of the sequence of red galaxies (RS) with the environment is
investigated using field, group, and cluster galaxies drawn from the SDSS. Our
work focuses in studying the mean colour ($\mu_R$) and the scatter ($\sigma_R$)
of the RS as a function absolute magnitude in different environments
characterised either by the mass of the system in which the galaxies are
located or by the distance to the system's centre. The same analysis is carried
out using red early type galaxies. For a given luminosity, $\mu_R$ of field
galaxies is bluer and $\sigma_R$ is larger than their group and cluster
counterparts irrespective of mass and position within the systems. Among
systems of galaxies, high mass groups and clusters have the reddest $\mu_R$ and
the smallest $\sigma_R$. These differences almost disappear when red early type
galaxies alone are considered. Galaxies in the core and in the outskirts of
groups have similar $\mu_R$, whereas galaxies in clusters show a strong
dependence on cluster centric distance. Red early type galaxies in the
outskirts of clusters have $\sigma_R$ values as large as field galaxies', while
galaxies in the inner regions of clusters have lower values. We find that
bright red early type galaxies have reached nearly the same evolutionary stage
in all environments. Our results suggest that the cluster environment is not
necessary to populate the RS. We propose a scenario in which the RS in massive
systems is populated by two different star formation history galaxies: red
early type galaxies that formed the bulk of their stars during the early stages
of massive halo assembly, and red galaxies that passed most of their lives
inhabiting poor groups or the field and fell into massive systems at lower
redshifts. |
Evidence for Environmentally Dependent Cluster Disruption in M83: Using multi-wavelength imaging from the Wide Field Camera 3 on the Hubble
Space Telescope we study the stellar cluster populations of two adjacent fields
in the nearby face-on spiral galaxy, M83. The observations cover the galactic
centre and reach out to ~6 kpc, thereby spanning a large range of environmental
conditions, ideal for testing empirical laws of cluster disruption. The
clusters are selected by visual inspection to be centrally concentrated,
symmetric, and resolved on the images. We find that a large fraction of objects
detected by automated algorithms (e.g. SExtractor or Daofind) are not clusters,
but rather are associations. These are likely to disperse into the field on
timescales of tens of Myr due to their lower stellar densities and not due to
gas expulsion (i.e. they were never gravitationally bound). We split the sample
into two discrete fields (inner and outer regions of the galaxy) and search for
evidence of environmentally dependent cluster disruption. Colour-colour
diagrams of the clusters, when compared to simple stellar population models,
already indicate that a much larger fraction of the clusters in the outer field
are older by tens of Myr than in the inner field. This impression is quantified
by estimating each cluster's properties (age, mass, and extinction) and
comparing the age/mass distributions between the two fields. Our results are
inconsistent with "universal" age and mass distributions of clusters, and
instead show that the ambient environment strongly affects the observed
populations. | A Soliton Solution for the Central Dark Masses in 47- Tuc Globular
Cluster and Implications for the Axiverse: We offer a standing wave explanation for the rising proper motions of stars
at the center of the globular cluster 47-Tucanae, amounting to $\simeq 0.44\%$
of the total mass. We show this can be explained as a solitonic core of dark
matter composed of light bosons, $ m \geq 10^{-18} eV $, corresponding to $
\leq 0.27 pc$, as an alternative to a single black hole (BH) or a concentration
of stellar BH remnants proposed recently. This is particularly important as
having a concentrated stellar BH remnant with the above radii is very
challenging without the heavy core since the three body encounters would
prevent the BHs to be that concentrated. We propose this core develops from
dark matter captured in the deep gravitational potential of this globular
cluster as it orbits the dark halo of our galaxy. This boson may be evidence
for a second light axion, additional to a lighter boson of $10^{-22} eV$,
favored for the dominant dark matter implied by the large dark cores of dwarf
spheroidal galaxies. The identification of two such light bosonic mass scales
favors the generic string theory prediction of a wide, discrete mass spectrum
of axionic scalar fields. |
Constraining Dwarf Spheroidal Dark Matter Halos With The Galactic Center
Excess: If the gamma-ray excess from the galactic center reported by Fermi-LAT is a
signal from annihilating dark matter, one must question why a similar excess
has not been observed in dwarf spheroidal galaxies. We use this observation to
place constraints on the density profile of dwarf spheroidal galaxies under the
assumption that the galactic center excess is in fact a signal from
annihilating dark matter. We place constraints on the generalized NFW parameter
$\gamma$ and the Einasto profile parameter $\alpha$ which control the
logarithmic slope of the inner regions of the halo's density profile. We
determine that under these assumptions the galactic center excess is
inconsistent with the standard NFW profile (and other `cuspy' profiles) for
dwarf spheroidal galaxies , but is consistent with observations of cored dwarf
galaxy profiles. Specifically, we find that dwarf spheroidal profiles must be
less cuspy than that of the Milky Way. Models of dark matter which
self-interacts through a light mediator can achieve this. | Inflationary vs. Reionization Features from Planck 2015 Data: Features during inflation and reionization leave corresponding features in
the temperature and polarization power spectra that could potentially explain
anomalies in the Planck 2015 data but require a joint analysis to disentangle.
We study the interplay between these two effects using a model-independent
parametrization of the inflationary power spectrum and the ionization history.
Preference for a sharp suppression of large scale power is driven by a feature
in the temperature power spectrum at multipoles $\ell \sim 20$, whereas
preference for a component of high redshift ionization is driven by a sharp
excess of polarization power at $\ell \sim 10$ when compared with the lowest
multipoles. Marginalizing inflationary freedom does not weaken the preference
for $z \gtrsim 10$ ionization, whereas marginalizing reionization freedom
slightly enhances the preference for an inflationary feature but can also mask
its direct signature in polarization. The inflation and reionization
interpretation of these features makes predictions for the polarization
spectrum which can be tested in future precision measurements especially at
$10\lesssim \ell \lesssim 40$. |
A Hydro-Particle-Mesh Code for Efficient and Rapid Simulations of the
Intracluster Medium: We introduce the cosmological HYPER code based on an innovative
hydro-particle-mesh (HPM) algorithm for efficient and rapid simulations of gas
and dark matter. For the HPM algorithm, we update the approach of Gnedin & Hui
(1998) to expand the scope of its application from the lower-density
intergalactic medium (IGM) to the higher-density intracluster medium (ICM).
While the original algorithm tracks only one effective particle species, the
updated version separately tracks the gas and dark matter particles as they do
not exactly trace each other on small scales. For the approximate hydrodynamics
solver, the pressure term in the gas equations of motion is calculated using
robust physical models. In particular, we use a dark matter halo model, ICM
pressure profile, and IGM temperature-density relation, all of which can be
systematically varied for parameter-space studies. We show that the HYPER
simulation results are in good agreement with the halo model expectations for
the density, temperature, and pressure radial profiles. Simulated galaxy
cluster scaling relations for Sunyaev-Zel'dovich (SZ) and X-ray observables are
also in good agreement with mean predictions, with scatter comparable to that
found in hydrodynamic simulations. HYPER also produces lightcone catalogs of
dark matter halos and full-sky tomographic maps of the lensing convergence, SZ
effect, and X-ray emission. These simulation products are useful for testing
data analysis pipelines, generating training data for machine learning,
understanding selection and systematic effects, and for interpreting
astrophysical and cosmological constraints. | Charting the Parameter Space of the 21-cm Power Spectrum: The high-redshift 21-cm signal of neutral hydrogen is expected to be observed
within the next decade and will reveal epochs of cosmic evolution that have
been previously inaccessible. Due to the lack of observations, many of the
astrophysical processes that took place at early times are poorly constrained.
In recent work we explored the astrophysical parameter space and the resulting
large variety of possible global (sky-averaged) 21-cm signals. Here we extend
our analysis to the fluctuations in the 21-cm signal, accounting for those
introduced by density and velocity, Ly$\alpha$ radiation, X-ray heating, and
ionization. While the radiation sources are usually highlighted, we find that
in many cases the density fluctuations play a significant role at intermediate
redshifts. Using both the power spectrum and its slope, we show that properties
of high-redshift sources can be extracted from the observable features of the
fluctuation pattern. For instance, the peak amplitude of ionization
fluctuations can be used to estimate whether heating occurred early or late
and, in the early case, to also deduce the cosmic mean ionized fraction at that
time. The slope of the power spectrum has a more universal redshift evolution
than the power spectrum itself and can thus be used more easily as a tracer of
high-redshift astrophysics. Its peaks can be used, for example, to estimate the
redshift of the Ly$\alpha$ coupling transition and the redshift of the heating
transition (and the mean gas temperature at that time). We also show that a
tight correlation is predicted between features of the power spectrum and of
the global signal, potentially yielding important consistency checks. |
Towards the use of asteroseismology to investigate the nature of dark
matter: The annihilation of huge quantities of captured dark matter (DM) particles
inside low-mass stars has been shown to change some of the stellar properties,
such as the star's effective temperature or the way the energy is transported
throughout the star. While in the classical picture, without DM, a star of 1
M_sun is expected to have a radiative interior during the main sequence, the
same star evolving in a halo of DM with a density rho_x > 10^8 GeV cm^-3 will
develop a convective core in order to evacuate the energy from DM annihilation
in a more efficient way. This convective core leaves a discontinuity in the
density and sound-speed profiles that can be detected by the analysis of the
stellar oscillations. In this paper we present an approach towards the use of
asteroseismology to detect the signature produced by the presence of DM inside
a star, and we propose a new methodology to infer the properties of a DM halo
from the stellar oscillations (such as the product of the DM density and the DM
particle-nucleon scattering cross-section). | Parity Asymmetry in the CMBR Temperature Power Spectrum: We study the power asymmetry between even and odd multipoles in the
multipolar expansion of CMB temperature data from WMAP, recently reported in
the literature. We introduce an alternate statistic which probes this effect
more sensitively. We find that the data is highly anomalous and consistently
outside $2\sigma$ significance level in the whole multipole range $l=[2,101]$.
We examine the possibility that this asymmetry may be caused by the foreground
cleaning procedure or by residual foregrounds. By direct simulations, using the
Planck Sky Model for foregrounds we rule out this possibility. We also examine
several possible sub-dominant foregrounds, which might lead to such an
asymmetry. However in all cases we are unable to explain the signal seen in
data. We next examine cleaned maps, using procedures other than the one
followed by the WMAP Science team. Specifically we analysed the maps cleaned by
the IPSE procedure, Needlets and the harmonic ILC procedure. In all these cases
we do not find a statistically significant signal of power asymmetry. This is
in contrast to the result obtained by the WMAP best fit power spectrum as well
as the ILC map. Finally, we test for the contribution of low-$l$ multipoles to
the observed power asymmetry. We find that if we eliminate the first six
multipoles, $l=[2,7]$, the significance falls below $2\sigma$ CL. Hence we find
that the signal gets dominant contribution from low-$l$ modes. |
Exit from Inflation with a First-Order Phase Transition and a
Gravitational Wave Blast: In double-field inflation, which exploits two scalar fields, one of the
fields rolls slowly during inflation whereas the other field is trapped in a
meta-stable vacuum. The nucleation rate from the false vacuum to the true one
becomes substantial enough that triggers a first order phase transition and
ends inflation. We revisit the question of first order phase transition in an
"extended" model of hybrid inflation, realizing the double-field inflationary
scenario, and correctly identify the parameter space that leads to a first
order phase transition at the end of inflation. We compute the gravitational
wave profile which is generated during this first order phase transition.
Assuming instant reheating, the peak frequency falls in the $1$ GHz to $10$ GHz
frequency band and the amplitude varies in the range $10^{-11}\lesssim
\Omega_{\rm GW} h^2 \lesssim 10^{-8}$, depending on the value of the
cosmological constant in the false vacuum. The signature could be observed by
the planned Chongqing high frequency gravitational probe. For a narrow band of
vacuum energies, the first order phase transition can happen after the end of
inflation via the violation of slow-roll, with a peak frequency that varies
from $1$ THz to $100$ THz. For smaller values of cosmological constant, even
though inflation can end via slow-roll violation, the universe gets trapped in
a false vacuum whose energy drives a second phase of eternal inflation. This
range of vacuum energies do not lead to viable inflationary models, unless the
value of the cosmological constant is compatible with the observed value,
$M\sim 10^{-3}$ eV. | Adiabatic contraction revisited: implications for primordial black holes: We simulate the adiabatic contraction of a dark matter (DM) distribution
during the process of the star formation, paying particular attention to the
phase space distribution of the DM particles after the contraction. Assuming
the initial uniform density and Maxwellian distribution of DM velocities, we
find that the number $n(r)$ of DM particles within the radius $r$ scales like
$n(r) \propto r^{1.5}$, leading to the DM density profile $\rho\propto
r^{-1.5}$, in agreement with the Liouville theorem and previous numerical
studies. At the same time, the number of DM particles $\nu(r)$ with periastra
smaller than $r$ is parametrically larger, $\nu(r) \propto r$, implying that
many particles contributing at any given moment into the density $\rho(r)$ at
small $r$ have very elongated orbits and spend most of their time at distances
larger than $r$. This has implications for the capture of DM by stars in the
process of their formation. As a concrete example we consider the case of
primordial black holes (PBH). We show that accounting for very eccentric orbits
boosts the amount of captured PBH by a factor of up to $2\times 10^3$ depending
on the PBH mass, improving correspondingly the previously derived constraints
on the PBH abundance. |
Light WIMPs And Equivalent Neutrinos: Very light WIMPs (chi), thermal relics that annihilate late in the early
Universe, change the energy and entropy densities at BBN and at recombination.
BBN, in combination with the CMB, can remove some of the degeneracies among
light WIMPs and equivalent neutrinos, constraining the existence and properties
of each. Depending on the nature of the light WIMP (Majorana or Dirac fermion,
real or complex scalar) the joint BBN + CMB analyses set lower bounds to m_chi
in the range 0.5 - 5 MeV (m_chi/m_e > 1 - 10), and they identify best fit
values for m_chi in the range 5 - 10 MeV. The joint BBN + CMB analysis finds a
best fit value for the number of equivalent neutrinos, Delta N_nu ~ 0.65,
nearly independent of the nature of the WIMP. In the absence of a light WIMP
(m_chi > 20 MeV), N_eff = 3.05(1 + Delta N_nu /3). In this case, there is
excellent agreement between BBN and the CMB, but the joint fit reveals Delta
N_nu = 0.40+-0.17, disfavoring standard big bang nucleosynthesis (SBBN) (Delta
N_nu = 0) at ~ 2.4 sigma, as well as a sterile neutrino (Delta N_nu = 1) at ~
3.5 sigma. The best BBN + CMB joint fit disfavors the absence of dark radiation
(Delta N_nu = 0 at ~ 95% confidence), while allowing for the presence of a
sterile neutrino (Delta N_nu = 1 at ~ 1 sigma). For all cases considered here,
the lithium problem persists. These results, presented at the TAUP 2013
Conference, are based on Nollett & Steigman (2013). | An Imaging and Spectroscopic Study of Four Strong MgII Absorbers
Revealed By GRB060418: We present results from an imaging and spectroscopic study of four strong
MgII absorbers of W(2796) >~ 1 Ang revealed by the afterglow of GRB060418 at
z_GRB=1.491. These absorbers, at z=0.603,0.656,1.107 and z_GRB, exhibit large
ion abundances that suggest neutral gas column densities characteristic of
damped Lya systems. The imaging data include optical images obtained using LRIS
on the Keck I telescope and using ACS on board HST, and near-infrared H-band
images obtained using PANIC on the Magellan Baade Telescope and K'-band images
obtained using NIRC2 with LGSAO on the Keck II telescope. These images reveal
six distinct objects at <~ 3.5'' of the afterglow's position, two of which
exhibit well-resolved mature disk morphology, one shows red colors, and three
are blue compact sources. Follow-up spectroscopic observations using LRIS
confirm that one of the disk galaxies coincides with the MgII absorber at
z=0.656. The observed broad-band spectral energy distributions of the second
disk galaxy and the red source indicate that they are associated with the
absorbers at z=0.603 and z=1.107, respectively. These results show that strong
MgII absorbers identified in GRB afterglow spectra are associated with typical
galaxies of luminosity ~ (0.1-1) L* at impact parameter <~ 10 h^-1 kpc. The
close angular separation would preclude easy detections toward a bright quasar.
Finally, we associate the remaining three blue compact sources with the GRB
host galaxy, noting that they are likely star-forming knots located at
projected distances 2-12 h^-1 kpc from the afterglow. At the afterglow's
position, we derive a 2-sigma upper limit to the underlying SFR intensity of
0.0074 M_sun yr^-1 kpc^-2. |
Herschel-ATLAS: blazars in the SDP field: To investigate the poorly constrained sub-mm counts and spectral properties
of blazars we searched for these in the Herschel-ATLAS (H-ATLAS) science
demostration phase (SDP) survey catalog. We cross-matched 500$\mu$m sources
brighter than 50 mJy with the FIRST radio catalogue. We found two blazars, both
previously known. Our study is among the first blind blazar searches at sub-mm
wavelengths, i.e., in the spectral regime where little is still known about the
blazar SEDs, but where the synchrotron peak of the most luminous blazars is
expected to occur. Our early results are consistent with educated
extrapolations of lower frequency counts and question indications of
substantial spectral curvature downwards and of spectral upturns at mm
wavelengths. One of the two blazars is identified with a Fermi/LAT $\gamma$-ray
source and a WMAP source. The physical parameters of the two blazars are
briefly discussed.These observations demonstrate that the H-ATLAS survey will
provide key information about the physics of blazars and their contribution to
sub-mm counts. | Primordial Black Holes and Slow-Roll Violation: For primordial black holes (PBH) to be the dark matter in single-field
inflation, the slow-roll approximation must be violated by at least ${\cal
O}(1)$ in order to enhance the curvature power spectrum within the required
number of efolds between CMB scales and PBH mass scales. Power spectrum
predictions which rely on the inflaton remaining on the slow-roll attractor can
fail dramatically leading to qualitatively incorrect conclusions in models like
an inflection potential and misestimate the mass scale in a running mass model.
We show that an optimized temporal evaluation of the Hubble slow-roll
parameters to second order remains a good description for a wide range of PBH
formation models where up to a $10^7$ amplification of power occurs in $10$
efolds or more. |
A test of the evolution of gas depletion factor in galaxy clusters using
strong gravitational lensing systems: In this letter, we discuss a new method to probe the redshift evolution of
the gas depletion factor, i.e. the ratio by which the gas mass fraction of
galaxy clusters is depleted with respect to the universal mean of baryon
fraction. The dataset we use for this purpose consists of 40 gas mass fraction
measurements measured at $r_{2500}$ using Chandra X-ray observations, strong
gravitational lensing sub-samples obtained from SLOAN Lens ACS + BOSS
Emission-line Lens Survey (BELLS) + Strong Legacy Survey SL2S + SLACS. For our
analysis, the validity of cosmic distance duality relation is assumed. We find
a mildly decreasing trend for the gas depletion factor as a function of
redshift at about 2.7$\sigma$. This is the first result in literature which
does not find a constant gas depletion factor as a function of redshift using
gas mass fraction measurements at $r_{2500}$. | Probing elastic interactions in the dark sector and the role of $S_8$: We place observational constraints on two models within a class of scenarios
featuring an elastic interaction between dark energy and dark matter that only
produces momentum exchange up to first order in cosmological perturbations. The
first one corresponds to a perfect-fluid model of the dark components with an
explicit interacting Lagrangian, where dark energy acts as a dark radiation at
early times and behaves as a cosmological constant at late times. The second
one is a dynamical dark energy model with a dark radiation component, where the
momentum exchange covariantly modifies the conservation equations in the dark
sector. Using Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations
(BAO), and Supernovae type Ia (SnIa) data, we show that the Hubble tension can
be alleviated due to the additional radiation, while the $\sigma_8$ tension
present in the $\Lambda$-Cold-Dark-Matter model can be eased by the weaker
galaxy clustering that occurs in these interacting models. Furthermore, we show
that, while CMB+BAO+SnIa data put only upper bounds on the coupling strength,
adding low-redshift data in the form of a constraint on the parameter $S_8$
strongly favours nonvanishing values of the interaction parameters. Our
findings are in line with other results in the literature that could signal a
universal trend of the momentum exchange among the dark sector. |
Large scale anisotropies on halo infall: We perform a statistical analysis of the peculiar velocity field around dark
matter haloes in numerical simulations. We examine different properties of the
infall of material onto haloes and its relation to central halo shapes and the
shape of the large scale surrounding regions (LSSR). We find that the amplitude
of the infall velocity field along the halo shape minor axis is larger than
that along the major axis. This is consistent for general triaxial haloes, and
for both prolate and oblate systems. We also report a strong anisotropy of the
velocity field along the principal axes of the LSSR. The infall velocity field
around dark matter haloes reaches a maximum value along the direction of the
minor axis of the LSSR, whereas along the direction of its major axis, it
exhibits the smallest velocities. We also analyse the dependence of the matter
velocity field on the local environment. The amplitude of the infall velocity
at high local density regions is larger than at low local density regions. The
velocity field tends to be more laminar along the direction towards the minor
axis of the LSSR, where the mean ratio between flow velocity and velocity
dispersion is of order unity and nearly constant up to scales of 15 Mpc/h. We
also detect anisotropies in the outflowing component of the velocity field,
showing a maximum amplitude along the surrounding LSSR major axis. | Hierarchical modeling and statistical calibration for photometric
redshifts: The cosmological exploitation of modern photometric galaxy surveys requires
both accurate (unbiased) and precise (narrow) redshift probability
distributions derived from broadband photometry. Existing methodologies do not
meet those requirements. Standard template fitting delivers interpretable
models and errors, but lacks flexibility to learn inaccuracies in the observed
photometry or the spectral templates. Machine learning addresses those issues,
but requires representative training data, and the resulting models and
uncertainties cannot be interpreted in the context of a physical model or
outside of the training data. We present a hierarchical modeling approach
simultaneously addressing the issues of flexibility, interpretability, and
generalization. It combines template fitting with flexible (machine
learning-like) models to correct the spectral templates, model their redshift
distributions, and recalibrate the photometric observations. By optimizing the
full posterior distribution of the model and solving for its (thousands of)
parameters, one can perform a global statistical calibration of the data and
the SED model. We apply this approach to the public Dark Energy Survey Science
Verification data, and show that it provides more accurate and compact redshift
posterior distributions than existing methods, as well as insights into
residual photometric and SED systematics. The model is causal, makes
predictions for future data (e.g., additional photometric bandpasses), and its
internal parameters and components are interpretable. This approach does not
formally require the training data to be complete or representative; in
principle it can even work in regimes in which few or no spectroscopic
redshifts are available. |
Globular Cluster Systems in Nearby Dwarf Galaxies: III. Formation
Efficiencies of Old Globular Clusters: We investigate the globular cluster (GC) system scaling parameters as a
function of galaxy mass, i.e. specific frequency (S_N), specific luminosity
(S_L), specific mass (S_M), and specific number (^T) of GCs. We sample the
entire range in galaxy luminosity (Mv = -11 to -23 mag = 10^6 - 10^11 L_sol),
environment, and morphology. Irrespective of galaxy type, we confirm the
increase of the S_N-value above and below a galaxy magnitude of Mv = -20 mag.
Over the full mass range, the S_L-value of early-type galaxies is, on average,
twice that of late-types. To investigate the observed trends we derive
theoretical predictions of GC system scaling parameters as a function of host
galaxy mass based on the models of Dekel & Birnboim (2006) in which
star-formation processes are regulated by stellar and supernova feedback below
a stellar mass of 3x10^10 M_sol, and by virial shocks above it. We find that
the analytical model describes remarkably well the shape of the GC system
scaling parameter distributions with a universal specific GC formation
efficiency, eta, which relates the total mass in GCs to the total galaxy halo
mass. Early-type and late-type galaxies show a similar mean value of eta =
5.5e-5, with an increasing scatter towards lower galaxy masses. This can be due
to the enhanced stochastic nature of the star and star-cluster formation
processes for such systems. Some massive galaxies have excess eta values
compared to what is expected from the mean model prediction for galaxies more
luminous than Mv = -20 mag (Lv=10^10L_sol). This may be attributed to a very
efficient early GC formation, less efficient production of field stars or
accretion of predominantly low-mass/luminosity high-eta galaxies, or a mixture
of all these effects. (Abridged) | Scaling Rrelation in two situations of extreme mergers: Clusters of galaxies are known to be dynamically active systems, yet X-ray
studies of the low redshift population exhibit tight scaling laws. In this
work, we extend previous studies of this apparent paradox using numerical
simulations of two extreme merger cases, one is a high Mach number (above 2.5)
satellite merger similar to the "bullet cluster" and the other a merger of
nearly equal mass progenitors. Creating X-ray images densely sampled in time,
we construct TX, Mgas, and YX measures within R500 and compare to the
calibrations of Kravtsov et al. (2006). We find that these extreme merger cases
respect the scaling relations, for both intrinsic measures and for measures
derived from appropriately masked, synthetic Chandra X-ray images. The masking
procedure plays a critical role in the X-ray temperature calculation while it
is irrelevant in the X-ray gas mass derivation. Mis-centering up to 100 kpc
does not influence the result. The observationally determined radius R500 might
conduce to systematic shifts in Mgas, and YX which increase the total mass
scatter. |
Photometric H alpha and [O II] Luminosity Function of SDF and SXDF
Galaxies: Implications for Future Baryon Oscillation Surveys: Efficient selection of emission line galaxies at z > 1 by photometric
information in wide field surveys is one of the keys for future spectroscopic
surveys to constrain dark energy using the baryon acoustic oscillation (BAO)
signature. Here we estimate the H alpha and [O II] line luminosity functions of
galaxies at z = 0.5-1.7 using a novel approach where multi-wavelength imaging
data is used to jointly estimate both photometric redshifts and star-formation
rates. These photometric estimates of line luminosities at high-redshift use
the large data sets of the Subaru Deep Field and Subaru XMM-Newton Deep Field
(covering \sim 1 deg^2) and are calibrated with the spectroscopic data of the
local Sloan Digital Sky Survey galaxies. The derived luminosity functions
(especially H alpha) are in reasonable agreement with the past estimates based
on spectroscopic or narrow-band-filter surveys. This dataset is useful for
examining the photometric selection of target galaxies for BAO surveys because
of the large cosmological volume covered and the large number of galaxies with
detailed photometric information. We use the sample to derive the photometric
and physical properties of emission line galaxies to assist planning for future
spectroscopic BAO surveys. We also show some examples of photometric selection
procedures which can efficiently select these emission line galaxies. | HACC Cosmological Simulations: First Data Release: We describe the first major public data release from cosmological simulations
carried out with Argonne's HACC code. This initial release covers a range of
datasets from large gravity-only simulations. The data products include halo
information for multiple redshifts, down-sampled particles, and lightcone
outputs. We provide data from two very large LCDM simulations as well as
beyond-LCDM simulations spanning eleven w0-wa cosmologies. Our release platform
uses Petrel, a research data service, located at the Argonne Leadership
Computing Facility. Petrel offers fast data transfer mechanisms and
authentication via Globus, enabling simple and efficient access to stored
datasets. Easy browsing of the available data products is provided via a web
portal that allows the user to navigate simulation products efficiently. The
data hub will be extended by adding more types of data products and by enabling
computational capabilities to allow direct interactions with simulation
results. |
A new HST/Herschel deep field at the North Ecliptic Pole: preparing the
way for JWST, SPICA and Euclid: We propose a co-ordinated multi-observatory survey at the North Ecliptic
Pole. This field is the natural extragalactic deep field location for most
space observatories (e.g. containing the deepest Planck, WISE and eROSITA
data), is in the continuous viewing zones for e.g. Herschel, HST, JWST, and is
a natural high-visibility field for the L2 halo orbit of SPICA with deep and
wide-field legacy surveys already planned. The field is also a likely deep
survey location for the forthcoming Euclid mission. It is already a
multi-wavelength legacy field in its own right (e.g. AKARI, LOFAR, SCUBA-2):
the outstanding and unparalleled continuous mid-IR photometric coverage in this
field and nowhere else enables a wide range of galaxy evolution diagnostics
unachievable in any other survey field, by spanning the wavelengths of
redshifted PAH and silicate features and the peak energy output of AGN hot
dust. We argue from the science needs of Euclid and JWST, and from the
comparative multiwavelength depths, that the logical approach is (1) a deep
(H-UDF) UV/optical tile in the NEP over ~10 square arcminutes, and (2) an
overlapping wide-field UV/optical HST survey tier covering >100 square
arcminutes, with co-ordinated submm SPIRE mapping up to or beyond the submm
point source confusion limit over a wider area and PACS data over the shallower
HST tier. | Extragalactic Globular Cluster Populations from High Resolution
Integrated Light Spectra: We present a comparison of high-resolution, integrated-light, detailed
chemical abundances for Galactic and extragalactic globular clusters in both
massive galaxies and dwarf galaxies. We include measurements of Fe, Ca, Si, Na,
and Al for globular cluster samples in the Milky Way, M31, Large Magellanic
Cloud, and NGC 5128. These and other recent results from our group on M31 and
NGC 5128 are the first chemical abundances derived from discrete absorption
features in old stars beyond the Milky Way and its nearest neighbors. These
abundances can provide both galaxy enrichment histories and constraints on
globular cluster formation and evolution. |
Angular ellipticity correlations in a composite alignment model for
elliptical and spiral galaxies and inference from weak lensing: We investigate a physical, composite alignment model for both spiral and
elliptical galaxies and its impact on cosmological parameter estimation from
weak lensing for a tomographic survey. Ellipticity correlation functions and
angular ellipticity spectra for spiral and elliptical galaxies are derived on
the basis of tidal interactions with the cosmic large-scale structure and
compared to the tomographic weak lensing signal. We find that elliptical
galaxies cause a contribution to the weak-lensing dominated ellipticity
correlation on intermediate angular scales between $\ell\simeq40$ and
$\ell\simeq400$ before that of spiral galaxies dominates on higher multipoles.
The predominant term on intermediate scales is the negative cross-correlation
between intrinsic alignments and weak gravitational lensing (GI-alignment). We
simulate parameter inference from weak gravitational lensing with intrinsic
alignments unaccounted; the bias induced by ignoring intrinsic alignments in a
survey like Euclid is shown to be several times larger than the statistical
error and can lead to faulty conclusions when comparing to other observations.
The biases generally point into different directions in parameter space, such
that in some cases one can observe a partial cancellation effect. Furthermore,
it is shown that the biases increase with the number of tomographic bins used
for the parameter estimation process. We quantify this parameter estimation
bias in units of the statistical error and compute the loss of Bayesian
evidence for a model due to the presence of systematic errors as well as the
Kullback-Leibler divergence to quantify the distance between the true model and
the wrongly inferred one. | Impact of nonlinear overdensity statistics on primordial black hole
abundance: It has been recently established that, if the nonlinear relationship between
the overdensity perturbations and the curvature perturbations are taken into
account, non-Gaussianity is introduced in the overdensity statistics which
alters the expected primordial black hole abundance. This is explored by using
the nonlinear relationship between the overdensities and curvature
perturbations up to second order where a negative skewness and positive
kurtosis aims at lowering and increasing the abundance while an abundance
comparable to Gaussian perturbations is obtained by adjusting the amplitude of
the curvature power spectrum. The effects of the nonvanishing skewness and
kurtosis are studied using a toy model Dirac delta and lognormal curvature
power spectra as well as one obtained from an $\alpha-$attractor model capable
of primordial black hole production. Finally, the nonlinear calculations using
Press-Schechter are compared with peaks theory. |
Future prospects in observational galaxy evolution: towards increased
resolution: Future prospects in observational galaxy evolution are reviewed from a
personal perspective. New insights will especially come from high-redshift
integral field kinematic data and similar low-redshift observations in very
large and definitive surveys. We will start to systematically probe the mass
structures of galaxies and their haloes via lensing from new imaging surveys
and upcoming near-IR spectroscopic surveys will finally obtain large numbers of
rest frame optical spectra at high-redshift routinely. ALMA will be an
important new ingredient, spatially resolving the molecular gas fuelling the
high star-formation rates seen in the early Universe. | Initial conditions and sampling for multifield inflation: We investigate the initial conditions problem for multifield inflation. In
these scenarios the pre-inflationary dynamics can be chaotic, increasing the
sensitivity of the onset of inflation to the initial data even in the
homogeneous limit. To analyze physically equivalent scenarios we compare
initial conditions at fixed energy. This ensures that each trajectory is
counted once and only once, since the energy density decreases monotonically.
We present a full analysis of hybrid inflation that reveals a greater degree of
long range order in the set of "successful" initial conditions than was
previously apparent. We explore the effective smoothing scale for the fractal
set of successful initial conditions induced by the finite duration of the
pre-inflationary phase. The role of the prior information used to specify the
initial data is discussed in terms of Bayesian sampling. |
Biased Tracers of Two Fluids in the Lagrangian Picture: We explore Lagrangian perturbation theory (LPT) for biased tracers in the
presence of two fluids, focusing on the case of cold dark matter (CDM) and
baryons. The presence of two fluids induces corrections to the Lagrangian bias
expansion and tracer advection, both of which we formulate as expansions in the
three linear modes of the Lagrangian equations of motion. We compute the
linear-order two-fluid corrections in the Zeldovich approximation, finding that
modifications to the bias expansion and tracer advection both enter as
percent-level corrections over a large range of wavenumbers at low redshift and
draw parallels with the Eulerian formalism. We then discuss nonlinear
corrections in the two-fluid picture, and calculate contributions from the
relative velocity effect ($\propto v_r^2$) at one loop order. Finally, we
conduct an exploratory Fisher analysis to assess the impact of two-fluid
corrections on baryon acoustic oscillations (BAO) measurements, finding that
while modest values of the relative bias parameters can introduce systematic
biases in the measured BAO scale of up to $0.5\, \sigma$, fitting for these
effects as additional parameters increases the error bar by less than $30\%$
across a wide range of bias values. | Host Galaxy Identification for Supernova Surveys: Host galaxy identification is a crucial step for modern supernova (SN)
surveys such as the Dark Energy Survey (DES) and the Large Synoptic Survey
Telescope (LSST), which will discover SNe by the thousands. Spectroscopic
resources are limited, so in the absence of real-time SN spectra these surveys
must rely on host galaxy spectra to obtain accurate redshifts for the Hubble
diagram and to improve photometric classification of SNe. In addition, SN
luminosities are known to correlate with host-galaxy properties. Therefore,
reliable identification of host galaxies is essential for cosmology and SN
science. We simulate SN events and their locations within their host galaxies
to develop and test methods for matching SNe to their hosts. We use both real
and simulated galaxy catalog data from the Advanced Camera for Surveys General
Catalog and MICECATv2.0, respectively. We also incorporate "hostless" SNe
residing in undetected faint hosts into our analysis, with an assumed hostless
rate of 5%. Our fully automated algorithm is run on catalog data and matches
SNe to their hosts with 91% accuracy. We find that including a machine learning
component, run after the initial matching algorithm, improves the accuracy
(purity) of the matching to 97% with a 2% cost in efficiency (true positive
rate). Although the exact results are dependent on the details of the survey
and the galaxy catalogs used, the method of identifying host galaxies we
outline here can be applied to any transient survey. |
Comprehensive Study of a z = 2.35 DLA Galaxy: Mass, Metallicity, Age,
Morphology and SFR from HST and VLT: We present a detailed study of the emission from a z = 2.35 galaxy that
causes damped Lyman-alpha absorption in the spectrum of the background QSO,
SDSS J 2222-0946. We present the results of extensive analyses of the stellar
continuum covering the rest frame optical-UV regime based on broad-band HST
imaging, and of spectroscopy from VLT/X-Shooter of the strong emission lines:
Ly-alpha, [OII], [OIII], [NII], H-alpha and H-beta. We compare the metallicity
from the absorption lines in the QSO spectrum with the oxygen abundance
inferred from the strong-line methods (R23 and N2). The two emission-line
methods yield consistent results: [O/H] = -0.30+/-0.13. Based on the absorption
lines in the QSO spectrum a metallicity of -0.49+/-0.05 is inferred at an
impact parameter of 6.3 kpc from the centre of the galaxy with a column density
of hydrogen of log(N_HI)=20.65+/-0.05. The star formation rates of the galaxy
from the UV continuum and H-alpha line can be reconciled assuming an amount of
reddening of E(B-V) = 0.06+/-0.01, giving an inferred SFR of 13+/-1 M_sun / yr
(assuming a Chabrier IMF). From the HST imaging, the galaxy associated with the
absorption is found to be a compact (re=1.12 kpc) object with a disc-like,
elongated (axis ratio 0.17) structure indicating that the galaxy is seen close
to edge on. Moreover, the absorbing gas is located almost perpendicularly above
the disc of the galaxy suggesting that the gas causing the absorption is not
co-rotating with the disc. We investigate the stellar and dynamical masses from
SED-fitting and emission-line widths, respectively, and find consistent results
of 2x10^9 M_sun. We suggest that the galaxy is a young proto-disc with evidence
for a galactic outflow of enriched gas. This galaxy hints at how star-forming
galaxies may be linked to the elusive population of damped Lyman-alpha
absorbers. | Pre-ALMA observations of GRBs in the mm/submm range: GRBs generate an afterglow emission that can be detected from radio to X-rays
during days, or even weeks after the initial explosion. The peak of this
emission crosses the mm/submm range during the first hours to days, making
their study in this range crucial for constraining the models. Observations
have been limited until now due to the low sensitivity of the observatories in
this range. We present observations of 10 GRB afterglows obtained from APEX and
SMA, as well as the first detection of a GRB with ALMA, and put them into
context with all the observations that have been published until now in the
spectral range that will be covered by ALMA. The catalogue of mm/submm
observations collected here is the largest to date and is composed of 102 GRBs,
of which 88 had afterglow observations, whereas the rest are host galaxy
searches. With our programmes, we contributed with data of 11 GRBs and the
discovery of 2 submm counterparts. In total, the full sample, including data
from the literature, has 22 afterglow detections with redshift ranging from
0.168 to 8.2. GRBs have been detected in mm/submm wavelengths with peak
luminosities spanning 2.5 orders of magnitude, the most luminous reaching
10^33erg s^-1 Hz^-1. We observe a correlation between the X-ray brightness at
0.5 days and the mm/submm peak brightness. Finally we give a rough estimate of
the distribution of peak flux densities of GRB afterglows, based on the current
mm/submm sample. Observations in the mm/submm bands have been shown to be
crucial for our understanding of the physics of GRBs, but have until now been
limited by the sensitivity of the observatories. With the start of the
operations at ALMA, the sensitivity will be increased by more than an order of
magnitude. Our estimates predict that, once completed, ALMA will detect up to
98% of the afterglows if observed during the passage of the peak synchrotron
emission. |
Tracking the Multifield Dynamics with Cosmological Data: A Monte Carlo
approach: We introduce a numerical method specifically designed for investigating
generic multifield models of inflation where a number of scalar fields $\phi^K$
are minimally coupled to gravity and live in a field space with a non-trivial
metric $G_{IJ}(\phi^K)$. Our algorithm consists of three main parts. Firstly,
we solve the field equations through the entire inflationary period, deriving
predictions for observable quantities such as the spectrum of scalar
perturbations, primordial gravitational waves, and isocurvature modes. We also
incorporate the transfer matrix formalism to track the behavior of adiabatic
and isocurvature modes on super-horizon scales and the transfer of entropy to
scalar modes after the horizon crossing. Secondly, we interface our algorithm
with Boltzmann integrator codes to compute the subsequent full cosmology,
including the cosmic microwave background anisotropies and polarization angular
power spectra. Finally, we develop a novel sampling algorithm able to
efficiently explore a large volume of the parameter space and identify a
sub-region where theoretical predictions agree with observations. In this way,
sampling over the initial conditions of the fields and the free parameters of
the models, we enable Monte Carlo analysis of multifield scenarios. We test all
the features of our approach by analyzing a specific model and deriving
constraints on its free parameters. Our methodology provides a robust framework
for studying multifield inflation, opening new avenues for future research in
the field. | Cores and the Kinematics of Early-Type Galaxies: I have combined the Emsellem et al. ATLAS3D rotation measures of a large
sample of early-type galaxies with HST-based classifications of their central
structure to characterize the rotation velocities of galaxies with cores. "Core
galaxies" rotate slowly, while "power-law galaxies" (galaxies that lack cores)
rotate rapidly, confirming the analysis of Faber et al. Significantly, the
amplitude of rotation sharply discriminates between the two types in the -19 >
Mv > -22 domain over which the two types coexist. The slow rotation in the
small set of core galaxies with Mv > -20, in particular, brings them into
concordance with the more massive core galaxies. The ATLAS3D "fast-rotating"
and "slow-rotating" early-type galaxies are essentially the same as power-law
and core galaxies, respectively, or the Kormendy & Bender two families of
elliptical galaxies based on rotation, isophote shape, and central structure.
The ATLAS3D fast rotators do include roughly half of the core galaxies, but
their rotation-amplitudes are always at the lower boundary of that subset.
Essentially all core galaxies have ATLAS3D rotation-amplitudes lambda_(R_e/2)
<= 0.25, while all galaxies with lambda_(R_e/2) > 0.25 and figure eccentricity
> 0.2 lack cores. Both figure rotation and the central structure of early-type
galaxies should be used together to separate systems that appear to have formed
from "wet" versus "dry" mergers. |
Confined Population III Enrichment and the Prospects for Prompt
Second-Generation Star Formation: It is widely recognized that nucleosynthetic output of the first, Population
III supernovae was a catalyst defining the character of subsequent stellar
generations. Most of the work on the earliest enrichment was carried out
assuming that the first stars were extremely massive and that the associated
supernovae were unusually energetic, enough to completely unbind the baryons in
the host cosmic minihalo and disperse the synthesized metals into the
intergalactic medium. Recent work, however, suggests that the first stars may
in fact have been somewhat less massive, with a characteristic mass scale of a
few tens of solar masses. We present a cosmological simulation following the
transport of the metals synthesized in a Population III supernova assuming that
it had an energy of 1e51 ergs, compatible with standard Type II supernovae. A
young supernova remnant is inserted in the first star's relic HII region in the
free expansion phase and is followed for 40 Myr employing adaptive mesh
refinement and Lagrangian tracer particle techniques. The supernova remnant
remains partially trapped within the minihalo and the thin snowplow shell
develops pronounced instability and fingering. Roughly half of the ejecta turn
around and fall back toward the center of the halo, with 1% of the ejecta
reaching the center in 30 kyr and 10% in 10 Myr. The average metallicity of the
combined returning ejecta and the pristine filaments feeding into the halo
center from the cosmic web is 0.001 - 0.01 Z_sun, but the two remain unmixed
until accreting onto the central hydrostatic core that is unresolved at the end
of the simulation. We conclude that if Population III stars had less extreme
masses, they promptly enriched the host minihalos with metals and triggered
Population II star formation. | A New interpretation of MOND based on Mach principle and an Unruh like
effect: A new interpretation is introduced for MOND based on the Sciama's
interpretation of Mach principle and an Unruh like effect, in the context of a
generalized equivalence principle. It is argued that in a locally accelerated
frame with acceleration $a$ the appearance of a Rindler horizon may give rise
to a constant acceleration $a_0$ as the local properties of cosmological
horizon or Hubble length. The total gravitational acceleration inside this
frame becomes the combination of $a$ with $a_0$. For $a\gg a_0$, the
conventional gravitational mass $m_g$ interacts with the dominant acceleration
as $m_g a$ and application of Sciama's interpretation leads to the standard
Newtonian dynamics. For $a\ll a_0$, however, a reduced gravitational mass
$\bar{m}_g$ interacts with the dominant acceleration as $\bar{m}_g a_0$ and the
application of Sciama's interpretation on this reduced gravitational mass leads
to MOND. This introduces a third proposal for MOND: {\it The modification of
gravitational mass}. |
Outer disks of lenticular galaxies: By studying the stellar population properties along the radius in 15 nearby
S0 galaxies, I have found that the outer stellar disks are mostly old, with the
SSP-equivalent ages of 8-15 Gyr, being often older than the bulges. This fact
puts into doubt a currently accepted paradigm that S0 galaxies have formed at
z=0.4 by quenching star formation in spiral galaxies. | Two confirmed compact elliptical galaxies in the Antlia cluster: We confirm the existence of two compact elliptical (cE) galaxies in the
central region of the Antlia cluster through MAGELLAN-MIKE and GEMINI-GMOS
spectra. Only about a dozen galaxies of this rare type are known today up to a
distance of 100 Mpc. With this finding, Antlia becomes the nearest galaxy
cluster harbouring more than one cE galaxy among its galaxy population. One of
these galaxies shows evidence of interaction with one of the giant ellipticals
that dominate the central region of the cluster. |
CCDM model from quantum particle creation: constraints on dark matter
mass: In this work the results from the quantum process of matter creation have
been used in order to constrain the mass of the dark matter particles in an
accelerated Cold Dark Matter model (Creation Cold Dark Matter, CCDM). In order
to take into account a back reaction effect due to the particle creation
phenomenon, it has been assumed a small deviation $\varepsilon$ for the scale
factor in the matter dominated era of the form $t^{\frac{2}{3}+\varepsilon}$.
Based on recent $H(z)$ data, the best fit values for the mass of dark matter
created particles and the $\varepsilon$ parameter have been found as
$m=1.6\times10^3$ GeV, restricted to a 68.3\% c.l. interval of
($1.5<m<6.3\times10^7$) GeV and $\varepsilon = -0.250^{+0.15}_{-0.096}$ at
68.3\% c.l. For these best fit values the model correctly recovers a transition
from decelerated to accelerated expansion and admits a positive creation rate
near the present era. Contrary to recent works in CCDM models where the
creation rate was phenomenologically derived, here we have used a quantum
mechanical result for the creation rate of real massive scalar particles, given
a self consistent justification for the physical process. This method also
indicates a possible solution to the so called "dark degeneracy", where one can
not distinguish if it is the quantum vacuum contribution or quantum particle
creation which accelerates the Universe expansion. | Constraints on the Hubble Parameter from galaxy clusters and the
Validity of the Cosmic Distance Duality Relation: Constraints on the Hubble parameter, $H_0$, via X-ray surface brightness and
Sunyaev-Zel'dovich effect (SZE) observations of the galaxy clusters depend on
the validity of the cosmic distance duality relation (DD relation), $\eta=
D_{L}(z)(1+z)^{-2}/D_{A}(z) = 1$, where $D_L$ and $D_A$ are the luminosity
distance and angular diameter distance (ADD), respectively. In this work, we
argue that if the DD relation does not hold the X-ray plus SZE technique
furnishes a $H^{*}_{0}=H_{0}/\eta^{2}$. We use 25 ADD of galaxy clusters to
obtain simultaneous constraints on $H_{0}$ and possible violation of the DD
relation in a flat $\Lambda$CDM model. Such a violation is parametrized by two
functions: $\eta(z) = 1 + \eta_{0}z$ and $\eta(z) = 1 + \eta_{0}z/(1+z)$, where
$\eta_0$ is a constant parameter quantifying possible departures from the
strict validity. Finally, by marginalizing on the $\eta_{0}$ in both
parameterizations, we obtain constraints on $H_0$ regardless of the validity of
the DD relation. For the linear and non linear $\eta(z)$ functions, we obtain
$H_{0}= 75^{+ 7}_{-7}$ km/s/Mpc and $H_{0}= 75^{+ 10}_{-7}$ km/s/Mpc,
respectively (without systematic erros). Our results support recent $H_{0}$
measurements by using X-ray and SZE observations of galaxy clusters which have
taken the distance duality as valid. |
Big Bang Nucleosynthesis and the Helium Isotope Ratio: The conventional approach to search for departures from the standard model of
physics during Big Bang Nucleosynthesis involves a careful, and subtle
measurement of the mass fraction of baryons consisting of helium. Recent
measurements of this quantity tentatively support new physics beyond the
standard model but, historically, this method has suffered from hidden
systematic uncertainties. In this letter, I show that a combined measurement of
the primordial deuterium abundance and the primordial helium isotope ratio has
the potential to provide a complementary and reliable probe of new physics
beyond the standard model. Using the recent determination of the primordial
deuterium abundance and assuming that the measured pre-solar 3He/4He meteoritic
abundance reflects the primordial value, a bound can be placed on the effective
number of neutrino species, Neff(BBN) = 3.01 (+0.95 -0.76, with 95 per cent
confidence). Although this value of Neff supports the standard model, it is
presently unclear if the pre-solar 3He/4He ratio reflects the primordial value.
New astrophysical measurements of the helium isotope ratio in near-pristine
environments, together with updated calculations and experimental values of
several important nuclear reactions (some of which are already being
attempted), will lead to much improved limits on possible departures from the
standard model. To this end, I describe an analysis strategy to measure the 3He
I flux emitted from nearby low metallicity H II regions. The proposed technique
can be attempted with the next generation of large telescopes, and will be
easier to realize in metal-poor H II regions with quiescent kinematics. | Radial HI Profiles at the Periphery of Galactic Disks: The Role of
Ionizing Background Radiation: Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in
the radial density profile at some distance from the center. Using 22 galaxies
with known HI distributions as an example, we discuss the question of whether
this effect can be associated exclusively with external ionizing radiation, as
is commonly assumed. We show that before the surface density reaches
$\sigma_{\textrm{HI}}\le 0.5 {\cal M}_\odot/{\textrm {pc}}^2$(the same for
galaxies of different types), it is hard to expect the gas to be fully ionized
by background radiation. For two of 13 galaxies with a sharp drop in the HI
profile, the "steepening" can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile
is closer to the center than if it was a consequence of ionization by
background radiation and, therefore, it should be caused by other factors. |
The Effect Of AGN Heating On The Low-Redshift Lyα Forest: We investigate the effects of AGN heating and the ultraviolet background on
the low-redshift Lyman-$\alpha$ forest column density distribution (CDD) using
the Illustris simulation. We show that Illustris reproduces observations at $z
=0.1$ in the column density range $10^{12.5} - 10^{13.5}$cm$^{-2}$, relevant
for the "photon underproduction crisis." We attribute this to the inclusion of
AGN feedback, which changes the gas distribution so as to mimic the effect of
extra photons, as well as the use of the Faucher-Gigu\`ere ultraviolet
background, which is more ionizing at $z=0.1$ than the Haardt & Madau
background previously considered. We show that the difference between
simulations run with smoothed particle hydrodynamics and simulations using a
moving mesh is small in this column density range but can be more significant
at larger column densities. We further consider the effect of supernova
feedback, Voigt profile fitting and finite resolution, all of which we show to
have little influence on the CDD. Finally, we identify a discrepancy between
our simulations and observations at column densities $10^{14} -
10^{16}$cm$^{-2}$, where Illustris produces too few absorbers, which suggests
the AGN feedback model should be further refined. Since the "photon
underproduction crisis" primarily affects lower column density systems, we
conclude that AGN feedback and standard ionizing background models can resolve
the crisis. | No Evidence for Dark Energy Dynamics from a Global Analysis of
Cosmological Data: We use a variant of principal component analysis to investigate the possible
temporal evolution of the dark energy equation of state, w(z). We constrain
w(z) in multiple redshift bins, utilizing the most recent data from Type Ia
supernovae, the cosmic microwave background, baryon acoustic oscillations, the
integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike
other recent analyses, we find no significant evidence for evolving dark
energy; the data remains completely consistent with a cosmological constant. We
also study the extent to which the time-evolution of the equation of state
would be constrained by a combination of current- and future-generation
surveys, such as Planck and the Joint Dark Energy Mission. |
Choose to smooth: Gaussian streaming with the truncated Zel'dovich
approximation: We calculate the dark matter halo correlation function in redshift space
using the Gaussian streaming model (GSM). To determine the scale dependent
functions entering the streaming model we use local Lagrangian bias together
with Convolution Lagrangian perturbation theory (CLPT) which constitutes an
approximation to the Post-Zel'dovich approximation. On the basis of N-body
simulations we demonstrate that a smoothing of the initial conditions with the
Lagrangian radius improves the Zel'dovich approximation and its ability to
predict the displacement field of proto-halos. Based on this observation we
implement a "truncated" CLPT by smoothing the initial power spectrum and
investigate the dependence of the streaming model ingredients on the smoothing
scale. We find that the real space correlation functions of halos and their
mean pairwise velocity are optimised if the coarse graining scale is chosen to
be 1 Mpc/h at z=0, while the pairwise velocity dispersion is optimised if the
smoothing scale is chosen to be the Lagrangian size of the halo. We compare
theoretical results for the halo correlation function in redshift space to
measurements within the Horizon Run 2 N-body simulation halo catalog. We find
that this simple two-filter smoothing procedure in the spirit of the truncated
Zel'dovich approximation significantly improves the GSM+CLPT prediction of the
redshift space halo correlation function over the whole mass range from large
galaxy to galaxy cluster-sized halos. | Characterizing the Sample Selection for Supernova Cosmology: Type Ia supernovae (SNe Ia) are used as distance indicators to infer the
cosmological parameters that specify the expansion history of the universe.
Parameter inference depends on the criteria by which the analysis SN sample is
selected. Only for the simplest selection criteria and population models can
the likelihood be calculated analytically, otherwise it needs to be determined
numerically, a process that inherently has error. Numerical errors in the
likelihood lead to errors in parameter inference. This article presents toy
examples where the distance modulus is inferred given a set of SNe at a single
redshift. Parameter estimators and their uncertainties are calculated using
Monte Carlo techniques. The relationship between the number of Monte Carlo
realizations and numerical errors is presented. The procedure can be applied to
more realistic models and used to determine the computational and data
management requirements of the transient analysis pipeline. |
3D Weak Lensing: Modified Theories of Gravity: Weak lensing (WL) promises to be a particularly sensitive probe of both the
growth of large scale structure (LSS) as well as the fundamental relation
between matter density perturbations and metric perturbations, thus providing a
powerful tool with which we may constrain modified theories of gravity (MG) on
cosmological scales. Future deep, wide-field WL surveys will provide an
unprecedented opportunity to constrain deviations from General Relativity (GR).
Employing a three-dimensional (3D) analysis based on the spherical
Fourier-Bessel (sFB) expansion, we investigate the extent to which MG theories
will be constrained by a typical 3D WL survey configuration including noise
from the intrinsic ellipticity distribution $\sigma_{\epsilon}$ of source
galaxies. Here we focus on two classes of screened theories of gravity: i)
$f(R)$ chameleon models and ii) environmentally dependent dilaton models. We
use one-loop perturbation theory combined with halo models in order to
accurately model the evolution of matter power-spectrum with redshift in these
theories. Using a Fisher information matrix based approach, we show that for an
all-sky spectroscopic survey, the parameter $f_{R_0}$ can be constrained in the
range $f_{R_0}< 5\times 10^{-6}(9\times 10^{-6})$ for $n=1(2)$ with a 3$\sigma$
confidence level. This can be achieved by using relatively low order angular
harmonics $\ell<100$. Including higher order harmonics $\ell>100$ can further
tighten the constraints, making them comparable to current solar-system
constraints. We also employ a Principal Component Analysis (PCA) in order to
study the parameter degeneracies in the MG parameters. Our results can
trivially be extended to other MG theories, such as the K-mouflage models. The
confusion from intrinsic ellipticity correlation and modification of the matter
power-spectrum at small scale due to feedback mechanisms is briefly discussed. | Detection of Diffuse Neutral Intragroup Medium in Hickson Compact Groups: We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (HI)
observations of a complete distance limited sample of 22 Hickson Compact Groups
(HCGs) with at least four true members. We detected an average HI mass of $8
\times 10^{9} M_{\odot}$ (median= $6\times 10^{9} M_{\odot}$), which is
significantly larger than previous single-dish measurements. Consequently, the
HI-deficiencies for these HCGs have been reduced, although not completely
eliminated. Spectral comparison of the GBT data with complementary Very Large
Array (VLA) data shows significant HI excess in the GBT spectra. The observed
excess is primarily due to the high surface brightness sensitivity of the GBT
detecting diffuse, low column density HI in these groups. The excess gas forms
a faint diffused neutral medium which is an intermediate stage in the evolution
of high-surface brightness HI tidal debris in the intra-group medium (IGM)
before it is fully ionized. The excess gas mass fraction (ratio of excess HI to
total HI) for our complete sample varies from 5% to 81% with an average of 36%
(median=30%). The excess gas mass fraction is highest in slightly HI deficient
groups where the tidal debris has had enough time to evolve. We also find the
excess gas content increases with the evolutionary phase of the group described
in Verdes-Montenegro et al. 2001. Theoretical calculations indicate that an HI
cloud of radius >200 pc would survive in an IGM of 2 million Kelvin for more
than the typical dynamical lifetime of a group. However, smaller clouds get
evaporated and assimilated into the hot IGM in a much shorter timescale. |
Active Galactic Nuclei - the Physics of Individual Sources and the
Cosmic History of Formation and Evolution: In this paper we give a brief review of the astrophysics of active galactic
nuclei (AGN). After a general introduction motivating the study of AGNs, we
discuss our present understanding of the inner workings of the central engines,
most likely accreting black holes with masses between a million and ten billion
solar masses. We highlight recent results concerning the jets (collimated
outflows) of AGNs derived from X-ray observations (Chandra) of kpc-scale jets
and gamma-ray observations of AGNs (Fermi, Cherenkov telescopes) with jets
closely aligned with the lines of sight (blazars), and discuss the
interpretation of these observations. Subsequently, we summarize our knowledge
about the cosmic history of AGN formation and evolution. We conclude with a
description of upcoming observational opportunities. | Lensing simulations by Taylor expansion -- not so inefficient after all: Cosmic Microwave Background lensing simulation by Taylor expansion has long
been considered impractical due to slow convergence, but a recent flat-sky
implementation shows that a simple trick eliminates this problem, making Taylor
lensing a fast and simple lensing algorithm for the flat sky. Here we
generalize the method to the full sky, and study its convergence and
performance relative to a commonly used numerical code, Lenspix, with extensive
benchmarks of both. Compared to the flat sky case, the method takes a speed hit
due to the slow speed of spherical harmonic transforms compared to fast Fourier
transforms, resulting in speeds of 1/3 to 2/3 of Lenspix for similar accuracy. |
The place of the Local Group in the cosmic web: We use the Bolshoi Simulation to find the most probable location of the Local
Group (LG) in the cosmic web. Our LG simulacra are pairs of halos with
isolation and kinematic properties consistent with observations. The cosmic web
is defined using a tidal tensor approach. We find that the LG's preferred
location is regions with a dark matter overdensity close to the cosmic average.
This makes filaments and sheets the preferred environment. We also find a
strong alignment between the LG and the cosmic web. The orbital angular
momentum is preferentially perpendicular to the smallest tidal eigenvector,
while the vector connecting the two halos is strongly aligned along the
smallest tidal eigenvector and perpendicular to the largest tidal eigenvector;
the pair lies and moves along filaments and sheets. We do not find any evidence
for an alignment between the spin of each halo in the pair and the cosmic web. | Optimal survey parameters: Ly$α$ and H$α$ intensity mapping
for synergy with the 21cm signal during reionization: Intensity mapping of multiple emission lines is emerging as a new branch to
astronomy, to probe both properties of ionizing sources and the medium between,
in particular the intergalactic medium. For Epoch of Reionization (EoR)
studies, both multi-line experiments and analysis methods are still in their
infancy. Here we explore optimal survey parameters for Ly$\alpha$ (and
H$\alpha$) intensity mapping up to high redshifts of reionization, and
requirements for optimised synergy with 21cm experiments. We investigate line
sensitivity, spectral resolution and detector pixel size requirements for
optimal (high signal-to-noise) mission output. Power and cross-power spectra in
a fiducial setup are derived, as are mock intensity maps. For line power
spectrum measurements a cumulative signal-to-noise of O$\left(10^3 \right)$,
and for respective cross-spectra with SKA 21cm observations of
O$\left(10\right)$ to O$\left(10^2\right)$ are possible per redshift bin around
the midpoint of reionization. These high signal-to-noise tomographic
measurements are in reach for line sensitivities $>8\times
10^{-18}$erg$\,$s$^{-1}$sr$^{-1}$Hz$^{-1}$, spectral resolution $R>250$ and
detector pixel sizes $<2\,$arcsec; all three requirements are met by the
proposed Cosmic Dawn Intensity Mapper (CDIM). For CDIM similar S/N values are
in reach for H$\alpha$. Already the planned NASA mission SPHEREx will detect
during the EoR Ly$\alpha$ autopower and cross power with 21cm, for
sensitivities better than $10^{-18}$erg$\,$s$^{-1}$sr$^{-1}$Hz$^{-1}$ in a
moderate 21cm foreground scenario (better than
$10^{-17}$erg$\,$s$^{-1}$sr$^{-1}$Hz$^{-1}$ in an optimistic scenario). We
advocate for IR missions in flavor of CDIM for a leap in IM and finish by
providing a cookbook for successful multi-line IM during the EoR. |
EFT of Inflation: Reflections on CMB and Forecasts on LSS Surveys: We investigate the possibility of constraining parameters of Effective Field
Theory (EFT) of inflation with upcoming Large Scale Structure (LSS) surveys in
order to have a better understanding of inflationary dynamics. With the
development of the construction algorithm of EFT, we arrive at a properly
truncated action for the entire scenario. Using this, we compute the two-point
correlation function for quantum fluctuations from Goldstone modes and related
inflationary observables in terms of coefficients of relevant EFT operators. We
then perform Fisher matrix forecast analysis to estimate the possible error
bars on the parameters of EFT as well as on the inflationary parameters using
two upcoming LSS surveys, namely, LSST and EUCLID. | Observational Constraints on $f(T)$ Gravity from Model-Independent Data: We establish new constraints on $f(T)$ gravity models by using cosmological
data. In particular, we investigate the restrictions given by the gas mass
fraction measurements of galaxy clusters and transversal BAO data. Both data
sets are regarded as weakly dependent on a fiducial cosmology. In addition, we
also include a CMB measurement of the temperature power spectrum first peak,
along with $H(z)$ values from cosmic chronometers and supernovae data from the
Pantheon data set. We also perform a forecast for future constraints on the
deviation of $f(T)$ models from the $\Lambda$CDM scenario by following the
specifications of the J-PAS and Euclid surveys and find significant
improvements on the constraints of the $b$-parameter, when compared to the
results of the statistical analysis. |
FIR measurements of Ly-$α$ emitters at z$\lesssim$1.0: dust
attenuation from PACS-\emph{Herschel}: One remaining open question regarding the physical properties of Ly$\alpha$
emitters (LAEs) is their dust content and its evolution with redshift. The
variety of results is large and with those reported by now is difficult to
establish clear relations between dust, other fundamental parameters of
galaxies (star-formation rate, metallicity or age) and redshift. In this
Letter, we report \emph{Herschel} PACS-100$\mu$m, PACS-160$\mu$m and
\emph{Spitzer} MIPS-24$\mu$m detections of a sample of spectroscopically
GALEX-selected LAEs at z$\sim$0.3 and $\sim$1.0. Five out of ten and one out of
two LAEs are detected in, at least, one PACS band at z$\sim$0.3 and $\sim$1.0,
respectively. These measurements have a great importance given that they allow
us to quantify, for the first time, the dust content of LAEs from direct FIR
observations. MIPS-24$\mu$m detections allow us to determine IR properties of
the PACS-undetected LAEs. We obtain that mid-IR/FIR detected star-forming (SF)
LAEs at z$\sim$0.3 have dust content within 0.75$\lesssim$ $A_{1200\AA}$
$\lesssim$2.0, with a median value of A$_{1200\textrm{\AA}}$$\sim$1.1. This
range broadens out to 0.75$\lesssim$ $A_{1200\AA}$ $\lesssim$2.5 when
considering those LAEs at z$\sim$1.0. Only one SF LAE is undetected both in
MIPS-24$\mu$m and PACS, with $A_{1200\AA}$ $\lesssim$0.75. These results seem
to be larger than those reported for high-redshift LAEs and, therefore,
although an evolutionary trend is not clearly seen, it could point out that
low-redshift LAEs are dustier than high-redshift ones. However, the diverse
methods used could introduce a systematic offset in the results. | The HST colours of high-redshift population III galaxies with strong
Lyman alpha emission: Population III galaxies, made partly or exclusively of metal-free stars, are
predicted to exist at high redshifts and may produce very strong Lya emission.
A substantial fraction of these Lya photons are likely absorbed in the
intergalactic medium at z>6, but recent simulations suggest that significant
Lya emission may be detectable up to z~8.5, i.e. well into the reionization
epoch. Here, we argue that high-redshift population III galaxies with strong
Lya emission can be identified in Hubble Space Telescope imaging data because
of their unusual colours. We quantify this effect in some of the filters used
in Y-band dropout searches for galaxies at z~8 and find that population III
galaxies with high Lya fluxes may exhibit much bluer J-H colours at z=8-10 than
any normal type of galaxy at these redshifts. This colour signature can arise
even if pop III stars account for as little as ~1e-3 to ~1e-2 of the stellar
mass in these galaxies. Some of the anomalously blue objects reported in
current Y-band dropout samples do in fact meet the colour criteria for
Lya-emitting population III galaxies. |
Fingerprint matching of beyond-WIMP dark matter: neural network approach: Galactic-scale structure is of particular interest since it provides
important clues to dark matter properties and its observation is improving.
Weakly interacting massive particles (WIMPs) behave as cold dark matter on
galactic scales, while beyond-WIMP candidates suppress galactic-scale structure
formation. Suppression in the linear matter power spectrum has been
conventionally characterized by a single parameter, the thermal warm dark
matter mass. On the other hand, the shape of suppression depends on the
underlying mechanism. It is necessary to introduce multiple parameters to cover
a wide range of beyond-WIMP models. Once multiple parameters are introduced, it
becomes harder to share results from one side to the other. In this work, we
propose adopting neural network technique to facilitate the communication
between the two sides. To demonstrate how to work out in a concrete manner, we
consider a simplified model of light feebly interacting massive particles. | Constraints on Light Hidden Sector Gauge Bosons from Supernova Cooling: We derive new bounds on hidden sector gauge bosons which could produce new
energy loss mechanisms in supernovae, enlarging the excluded region in
mass-coupling space by a significant factor compared to earlier estimates. Both
considerations of trapping and possible decay of these particles need to be
incorporated when determining such bounds, as does scattering on both neutrons
and protons. For masses and couplings near the region which saturates current
bounds, a significant background of such gauge bosons may also be produced due
to the cumulative effects of all supernovae over cosmic history. |
Investigation of the New Local Group Galaxy VV 124: We present the results of our stellar photometry and spectroscopy for the new
Local Group galaxy VV 124 (UGC 4879) obtained with the 6-m BTA telescope. The
presence of a few bright supergiants in the galaxy indicates that the current
star formation process is weak. The apparent distribution of stars with
different ages in VV 124 does not differ from the analogous distributions of
stars in irregular galaxies, but the ratio of the numbers of young and old
stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The
old stars (red giants) form the most extended structure, a thick disk with an
exponential decrease in the star number density to the edge. Definitely, the
young population unresolvable in images makes a great contribution to the
background emission from the central galactic regions. The presence of young
stars is also confirmed by the [O III] emission line visible in the spectra
that belongs to extensive diffuse galactic regions. The mean radial velocity of
several components (two bright supergiants, the unresolvable stellar
population, and the diffuse gas) is v_h = -70+/-15 km/s and the velocity with
which VV 124 falls into the Local Group is v_LG = -12+/-15 km/s. We confirm the
distance to the galaxy D = 1.1+/-0.1 Mpc and the metallicity of red giants
([Fe/H] = -1.37) found by Kopylov et al. (2008).VV 124 is located on the
periphery of the Local Group approximately at the same distance from M 31 and
our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it
is 0.5 Mpc away. | Gravitational-Wave Fringes at LIGO: Detecting Compact Dark Matter by
Gravitational Lensing: Utilizing gravitational-wave (GW) lensing opens a new way to understand the
small-scale structure of the universe. We show that, in spite of its coarse
angular resolution and short duration of observation, LIGO can detect the GW
lensing induced by compact structures, in particular by compact dark matter
(DM) or primordial black holes of $10 - 10^5 \, M_\odot$, which remain
interesting DM candidates. The lensing is detected through GW frequency
chirping, creating the natural and rapid change of lensing patterns:
\emph{frequency-dependent amplification and modulation} of GW waveforms. As a
highest-frequency GW detector, LIGO is a unique GW lab to probe such light
compact DM. With the design sensitivity of Advanced LIGO, one-year observation
by three detectors can optimistically constrain the compact DM density fraction
$f_{\rm DM}$ to the level of a few percent. |
Frequentist comparison of CMB local extrema statistics in the five-year
WMAP data with two anisotropic cosmological models: We present local extrema studies of two models that introduce a preferred
direction into the observed cosmic microwave background (CMB) temperature
field. In particular, we make a frequentist comparison of the one- and
two-point statistics for the dipole modulation and ACW models with data from
the five-year Wilkinson Microwave Anisotropy Probe (WMAP). This analysis is
motivated by previously revealed anomalies in the WMAP data, and particularly
the difference in the statistical nature of the temperature anisotropies when
analysed in hemispherical partitions.
The analysis of the one-point statistics indicates that the previously
determined hemispherical variance difficulties can be apparently overcome by a
dipole modulation field, but new inconsistencies arise if the mean and the
l-dependence of the statistics are considered. The two-point correlation
functions of the local extrema, the temperature pair product and the
point-point spatial pair-count, demonstrate that the impact of such a
modulation is to over-`asymmetrise' the temperature field on smaller scales
than the wave-length of the dipole or quadrupole, and this is disfavored by the
observed data.The results from the ACW model predictions, however, are
consistent with the standard isotropic hypothesis. The two-point analysis
confirms that the impact of this type of violation of isotropy on the
temperature extrema statistics is relatively weak.
From this work, we conclude that a model with more spatial structure than the
dipole modulated or rotational-invariance breaking models are required to fully
explain the observed large-scale anomalies in the WMAP data. | The follow-up EVN observations of twelve GPS radio sources at 5 GHz: We defined a sub-sample of twelve GPS sources which have not been observed
with the VLBI before, from the Parkes half-Jansky sample, and carried out VLBI
observations at 1.6 GHz and 5 GHz with the European VLBI Network (EVN) in 2006
and 2008, respectively, to classify the source structure and to find compact
symmetric objects (CSOs). Additionally, we carried out the 4.85 GHz flux
density observations for these sources with the Urumqi 25-m telescope between
the years 2007 and 2009 to study whether there is any variability in the total
flux density of the GPS sources. The results of the 5 GHz VLBI observations and
total flux densities of these sources are presented in this paper. From the
VLBI morphologies, the spectral indices of components and the total flux
variability of the twelve targets, we firmly classify three sources J0210+0419,
J1135$-$0021, and J2058+0540 as CSOs, and classify J1057+0012, J1203+0414, and
J1600$-$0037 as core-jet sources. The others J0323+0534, J0433$-$0229,
J0913+1454, J1109+1043, and J1352+0232 are labelled CSO candidates, and
J1352+1107 is a complex feature. Apart from core-jet sources, the total flux
densities of the CSOs and candidates are quite stable at 5 GHz both during a
long-term of $\sim$20 years relative to the PKS90 data and in a period between
2007 and 2009. The total flux densities are resolved-out by more than 20\% in
the 5 GHz VLBI images for 6 sources, probably because of diffuse emission. In
addition, we estimated the jet viewing angles $\Theta$ for the confirmed CSOs
by using the double-lobe flux ratio of the sources, the result being indicative
of relatively large $\Theta$ for the CSOs. |
Lost Horizon: Quantifying the Effect of Local Topography on Global 21-cm
Cosmology Data Analysis: We present an investigation of the horizon and its effect on global 21-cm
observations and analysis. We find that the horizon cannot be ignored when
modeling low frequency observations. Even if the sky and antenna beam are known
exactly, forward models cannot fully describe the beam-weighted foreground
component without accurate knowledge of the horizon. When fitting data to
extract the 21-cm signal, a single time-averaged spectrum or independent
multi-spectrum fits may be able to compensate for the bias imposed by the
horizon. However, these types of fits lack constraining power on the 21-cm
signal, leading to large uncertainties on the signal extraction, in some cases
larger in magnitude than the 21-cm signal itself. A significant decrease in
signal uncertainty can be achieved by performing multi-spectrum fits in which
the spectra are modeled simultaneously with common parameters. The cost of this
greatly increased constraining power, however, is that the time dependence of
the horizon's effect, which is more complex than its spectral dependence, must
be precisely modeled to achieve a good fit. To aid in modeling the horizon, we
present an algorithm and Python package for calculating the horizon profile
from a given observation site using elevation data. We also address several
practical concerns such as pixelization error, uncertainty in the horizon
profile, and foreground obstructions such as surrounding buildings and
vegetation. We demonstrate that our training set-based analysis pipeline can
account for all of these factors to model the horizon well enough to precisely
extract the 21-cm signal from simulated observations. | COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X.
Modeling based on high-precision astrometry of a sample of 25 lensed quasars:
consequences for ellipticity, shear, and astrometric anomalies: (abridged) Gravitationally lensed quasars can be used as powerful
cosmological and astrophysical probes. We can (i) infer the Hubble constant
based on the time-delay technique, (ii) unveil substructures along the l.o.s.
toward distant galaxies, and (iii) compare the shape and the slope of baryons
and dark matter distributions in galaxies. To reach these goals, we need
high-accuracy astrometry and morphology measurements of the lens. In this work,
we first present new astrometry for 11 lenses with measured time delays. Using
MCS deconvolution on NIC2 HST images, we reached an astrometric accuracy of
about 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second,
we combined these measurements with those of 14 other systems to present new
mass models of these lenses. This led to the following results: 1) In 4
double-image quasars, we show that the influence of the lens environment on the
time delay can easily be quantified and modeled, hence putting these lenses
with high priority for time-delay determination. 2) For quadruple-image
quasars, the difficulty often encountered in reproducing the image positions to
milli-arcsec accuracy (astrometric anomaly) is overcome by explicitly including
the nearest visible galaxy in the model. However, one anomalous system
(J1131-1231) does not show any luminous perturber in its vicinity, and three
others (WFI2026-4536, WFI2033-4723, and B2045+265) have problematic modeling.
These 4 systems are the best candidates for a pertubation by a dark matter
substructure. 3) We find a significant correlation between the PA of the light
and of the mass distributions in lensing galaxies. In contrast with other
studies, we find that the ellipticity of the light and of the mass also
correlate well, suggesting that the overall spatial distribution of matter is
not very different from the baryon distribution in the inner \sim 5 kpc of
lensing galaxies. |
Constraints on mixed dark matter from anomalous strong lens systems: Recently it has been claimed that the warm dark matter (WDM) model cannot at
the same time reproduce the observed Lyman-{\alpha} forests in distant quasar
spectra and solve the small-scale issues in the cold dark matter (CDM) model.
As an alternative candidate, it was shown that the mixed dark matter (MDM)
model that consists of WDM and CDM can satisfy the constraint from
Lyman-{\alpha} forests and account for the "missing satellite problem" as well
as the reported 3.5 keV anomalous X-ray line. We investigate observational
constraints on the MDM model using strong gravitational lenses. We first
develop a fitting formula for the nonlinear power spectra in the MDM model by
performing N-body simulations and estimate the expected perturbations caused by
line-of-sight structures in four quadruply lensed quasars that show anomaly in
the flux ratios. Our analysis indicates that the MDM model is compatible with
the observed anomaly if the mass fraction of the warm component is smaller than
0.47 at the 95% confidence level. The MDM explanation to the anomalous X-ray
line and the small-scale issues is still viable even after this constraint is
taken into account. | The Globular Cluster Systems of Abell 1185: We examine the properties of a previously discovered population of globular
clusters in the heart of the rich galaxy cluster Abell 1185 that might be
intergalactic in nature. Deep images obtained with the Advanced Camera for
Surveys (ACS) aboard Hubble Space Telescope (HST) confirm the presence of ~
1300 globular clusters brighter than I_{F814W} = 27.3 mag in a field devoid of
any large galaxies. The luminosities and colors of these objects are found to
be similar to those of metal-poor globular clusters observed in many galaxies
to date. Although a significant fraction of the detected globular clusters
undoubtedly reside in the outer halos of galaxies adjacent to this field,
detailed modeling of their distribution suggests that the majority of these
objects are likely to be intergalactic, in the sense that they are not
gravitationally bound to any individual galaxy. We conclude that the true
nature and origin of the globular cluster population in the core of A1185 --
galactic residents or intergalactic wanderers -- remains uncertain, and suggest
how future observation could resolve this ambiguity. |
Carbon monoxide and ionized carbon line emission global signals:
foregrounds and targets for absolute microwave spectrometry: (abr.) We consider the potential of future microwave spectrometers akin to
PIXIE in light of the sky-averaged global signal expected from the total
intensity of extragalactic carbon monoxide (CO) and ionized carbon ([CII]) line
emission. We start from models originally developed for forecasts of
line-intensity mapping (LIM) observations targeting the same line emission at
specific redshifts, extrapolating them across all of cosmic time. We then
calculate Fisher forecasts for uncertainties on parameters describing relic
spectral deviations, the CO/[CII] global signal, and a range of other Galactic
and extragalactic foregrounds considered in previous work. We find that the
measurement of the CO/[CII] global signal with a future CMB spectrometer
presents an exciting opportunity to constrain the evolution of metallicity and
molecular gas in galaxies across cosmic time. From PIXIE to its enhanced
version, SuperPIXIE, microwave spectrometers would have the fundamental
sensitivity to constrain the redshift evolution of average kinetic temperature
and cosmic molecular gas density at a level of 10% to 1%, respectively. Taking
a spectral distortion-centric perspective, when combined with other
foregrounds, sky-averaged CO/[CII] emission can mimic $\mu$- and to a lesser
extent $y$-type distortions. Under fiducial parameters, marginalising over the
CO/[CII] model parameters increases the error on $\mu$ by $\simeq50$%, and the
error on $y$ by $\simeq10$%. Incorporating information from planned CO LIM
surveys can recover some of this loss in precision. Future work should deploy a
more general treatment of the microwave sky to quantify in more detail the
potential synergies between PIXIE-like and CO LIM experiments, which complement
each other strongly in breadth versus depth, and ways to optimise both
spectrometer and LIM surveys to improve foreground cleaning and maximise the
science return for each. | The Lyman-$α$ forest in optically-thin hydrodynamical simulations: We study the statistics of the Lyman-$\alpha$ forest in a flat LCDM cosmology
with the N-body + Eulerian hydrodynamics code Nyx. We produce a suite of
simulations, covering the observationally relevant redshift range $2 \leq z
\leq 4$. We find that a grid resolution of 20 kpc/h is required to produce one
percent convergence of Lyman-$\alpha$ flux statistics, up to k = 10 h/Mpc. In
addition to establishing resolution requirements, we study the effects of
missing modes in these simulations, and find that box sizes of L > 40 Mpc/h are
needed to suppress numerical errors to a sub-percent level. Our optically-thin
simulations with the ionizing background prescription of Haardt & Madau (2012)
reproduce an IGM equation of state with $T_0 \approx 10^4 K$ and $\gamma
\approx 1.55$ at z=2, with a mean transmitted flux close to the observed
values. When using the ionizing background prescription of Faucher-Giguere et
al. (2009), the mean flux is 10-15 per cent below observed values at z=2, and a
factor of 2 too small at z = 4. We show the effects of the common practice of
rescaling optical depths to the observed mean flux and how it affects
convergence rates. We also investigate the common practice of `splicing'
results from a number of different simulations to estimate the 1D flux power
spectrum and show it is accurate at the 10 percent level. Finally, we find that
collisional heating of the gas from dark matter particles is negligible in
modern cosmological simulations. |
Primordial Non-Gaussianity Estimation using 21 cm Tomography from the
Epoch of Reionization: Measuring the small primordial nonGaussianity (PNG) predicted by cosmic
inflation theories may help diagnose them. The detectability of PNG by its
imprint on the 21cm power spectrum from the epoch of reionization is reassessed
here in terms of $f_{NL}$, the local nonlinearity parameter. We find that an
optimum, multi-frequency observation by SKA can achieve $\Delta f_{NL} \sim 3$
(comparable to recent Planck CMB limits), while a cosmic-variance-limited array
of this size like Omniscope can even detect $\Delta f_{NL} \sim 0.2$. This
substantially revises the methods and results of previous work. | Light Primordial Exotic Compact Objects as All Dark Matter: The radiation emitted by horizonless exotic compact objects (ECOs), such as
wormholes, 2-2-holes, fuzzballs, gravastars, boson stars, collapsed polymers,
superspinars etc., is expected to be strongly suppressed when compared to the
radiation of black holes. If large primordial curvature fluctuations collapse
into such objects instead of black holes, they do not evaporate or evaporate
much slower than black holes and could thus constitute all of the dark matter
with masses below $M < 10^{-16}M_\odot.$ We reevaluate the relevant
experimental constraints for light ECOs in this mass range and show that very
large new parameter space down to ECO masses $M\sim 10\,{\rm TeV}$ opens up for
light primordial dark matter. A new dedicated experimental program is needed to
test this mass range of primordial dark matter. |
Suites of dwarfs around nearby giant galaxies: We consider a sample of the Updated Nearby Galaxy Catalog that contains eight
hundred objects within 11 Mpc. Environment of each galaxy was characterized by
a tidal index $\Theta_1$ depending on the separation and mass of the galaxy's
Main Disturber (=MD). We ascribed the UNGC galaxies with a common MD to its
suite, and ranked suite members according to their $\Theta_1$. All suite
members with positive $\Theta_1$ are assumed to be physical companions of the
MD. The distribution of suites by the number of members, n, follows to a
relation $N(n) \sim n^{-2}$. The twenty most populated suites contain 468
galaxies, i.e. 59% of the UNGC sample. About 58% of our sample are members of
physical groups. The fraction of MDs among the brightest galaxies is almost
100% and drops to 50% at $M_B = -18^m$. We discuss various properties of MDs,
as well as galaxies belonging to their suites. The suite abundance practically
does not depend on morphological type, linear diameter or hydrogen mass of MD,
revealing the tightest correlation with the MD dynamical mass. Dwarf galaxies
around MDs exhibit well-known segregation effects: the members of outskirts
have later morphological types, richer HI-contents and higher rates of star
formation activity. Nevertheless, there are some intriguing cases when dwarf
spheroidal galaxies occur at the far periphery of the suites, as well as some
late-type dwarfs residing close to MDs. The multiplicity of nearby groups
according to number of their physical members can be described by the
Hirsh-like index $h_g = 9$, indicating that the Local Volume contains 9 groups
with populations exceeding 9 members. (abridged) | The local radio-galaxy population at 20 GHz: We have made the first detailed study of the high-frequency radio-source
population in the local universe, using a sample of 202 radio sources from the
Australia Telescope 20 GHz (AT20G) survey identified with galaxies from the 6dF
Galaxy Survey (6dFGS). The AT20G-6dFGS galaxies have a median redshift of
z=0.058 and span a wide range in radio luminosity, allowing us to make the
first measurement of the local radio luminosity function at 20 GHz.
Our sample includes some classical FR-1 and FR-2 radio galaxies, but most of
the AT20G-6dFGS galaxies host compact (FR-0) radio AGN which appear lack
extended radio emission even at lower frequencies. Most of these FR-0 sources
show no evidence for relativistic beaming, and the FR-0 class appears to be a
mixed population which includes young Compact Steep-Spectrum (CSS) and
Gigahertz-Peaked Spectrum (GPS) radio galaxies.
We see a strong dichotomy in the Wide-field Infrared Survey Explorer (WISE)
mid-infrared colours of the host galaxies of FR-1 and FR-2 radio sources, with
the FR-1 systems found almost exclusively in WISE `early-type' galaxies and the
FR-2 radio sources in WISE `late-type' galaxies.
The host galaxies of the flat- and steep-spectrum radio sources have a
similar distribution in both K--band luminosity and WISE colours, though
galaxies with flat-spectrum sources are more likely to show weak emission lines
in their optical spectra. We conclude that these flat-spectrum and
steep-spectrum radio sources mainly represent different stages in radio-galaxy
evolution, rather than beamed and unbeamed radio-source populations. |
Filament Hunting: Integrated HI 21cm Emission From Filaments Inferred by
Galaxy Surveys: Large scale filaments, with lengths that can reach tens of Mpc, are the most
prominent features in the cosmic web. These filaments have only been observed
indirectly through the positions of galaxies in large galaxy surveys or through
absorption features in the spectra of high redshift sources. In this study we
propose to go one step further and directly detect intergalactic medium
filaments through their emission in the HI 21cm line. We make use of high
resolution cosmological simulations to estimate the intensity of this emission
in low redshift filaments and use it to make predictions for the direct
detectability of specific filaments previously inferred from galaxy surveys, in
particular the Sloan Digital Sky Survey. Given the expected signal of these
filaments our study shows that HI emission from large filaments can be observed
by current and next generation radio telescopes. We estimate that gas in
filaments of length $l \gtrsim$ 15 $h^{-1}$Mpc with relatively small
inclinations to the line of sight ($\lesssim 10^\circ$) can be observed in
$\sim40-100$ hours with telescopes such as GMRT or EVLA, potentially providing
large improvements over our knowledge of the astrophysical properties of these
filaments. Due to their large field of view and sufficiently long integration
times, upcoming HI surveys with the Apertif and ASKAP instruments will be able
to detect large filaments independently of their orientation and curvature.
Furthermore, our estimates indicate that a more powerful future radio telescope
like SKA-2 can be used to map most of these filaments, which will allow them to
be used as a strong cosmological probe. | No new cosmological concordance with massive sterile neutrinos: It has been claimed recently that massive sterile neutrinos could bring about
a new concordance between observations of the cosmic microwave background
(CMB), the large-scale structure (LSS) of the Universe, and local measurements
of the Hubble constant, $H_0$. We demonstrate that this apparent concordance
results from combining datasets which are in significant tension, even within
this extended model, possibly indicating remaining systematic biases in the
measurements. We further show that this tension remains when the cosmological
model is further extended to include significant tensor modes, as suggested by
the recent BICEP2 results. Using the Bayesian evidence, we show that the
minimal $\Lambda$CDM model is strongly favoured over its neutrino extensions by
various combinations of datasets. Robust data combinations yield stringent
limits of $\sum m_\nu\lesssim0.3$ eV and $m_{\nu,{\rm sterile}}^{\rm eff}
\lesssim 0.3$ eV at $95\%$ CL for the sum of active and sterile neutrinos,
respectively. |
A Stellar Dynamical Mass Measurement of the Black Hole in NGC 3998 from
Keck Adaptive Optics Observations: We present a new stellar dynamical mass measurement of the black hole in the
nearby, S0 galaxy NGC 3998. By combining laser guide star adaptive optics
observations obtained with the OH-Suppressing Infrared Imaging Spectrograph on
the Keck II telescope with long-slit spectroscopy from the Hubble Space
Telescope and the Keck I telescope, we map out the stellar kinematics on both
small spatial scales, well within the black hole sphere of influence, and on
large scales. We find that the galaxy is rapidly rotating and exhibits a sharp
central peak in the velocity dispersion. Using the kinematics and the stellar
luminosity density derived from imaging observations, we construct
three-integral, orbit-based, triaxial stellar dynamical models. We find the
black hole has a mass of M_BH = (8.1_{-1.9}^{+2.0}) x 10^8 M_sun, with an
I-band stellar mass-to-light ratio of M/L = 5.0_{-0.4}^{+0.3} M_sun/L_sun
(3-sigma uncertainties), and that the intrinsic shape of the galaxy is very
round, but oblate. With the work presented here, NGC 3998 is now one of a very
small number of galaxies for which both stellar and gas dynamical modeling have
been used to measure the mass of the black hole. The stellar dynamical mass is
nearly a factor of four larger than the previous gas dynamical black hole mass
measurement. Given that this cross-check has so far only been attempted on a
few galaxies with mixed results, carrying out similar studies in other objects
is essential for quantifying the magnitude and distribution of the cosmic
scatter in the black hole mass - host galaxy relations. | The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
measurement of the BAO and growth rate of structure of the luminous red
galaxy sample from the anisotropic power spectrum between redshifts 0.6 and
1.0: We analyse the clustering of the Sloan Digital Sky Survey IV extended Baryon
Oscillation Spectroscopic Survey Data Release 16 luminous red galaxy sample
(DR16 eBOSS LRG) in combination with the high redshift tail of the Sloan
Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data Release 12
(DR12 BOSS CMASS). We measure the redshift space distortions (RSD) and also
extract the longitudinal and transverse baryonic acoustic oscillation (BAO)
scale from the anisotropic power spectrum signal inferred from 377,458 galaxies
between redshifts 0.6 and 1.0, with effective redshift of $z_{\rm eff}=0.698$
and effective comoving volume of $2.72\,{\rm Gpc}^3$. After applying
reconstruction we measure the BAO scale and infer $D_H(z_{\rm eff})/r_{\rm
drag} = 19.30\pm 0.56$ and $D_M(z_{\rm eff})/r_{\rm drag} =17.86 \pm 0.37$.
When we perform a redshift space distortions analysis on the pre-reconstructed
catalogue on the monopole, quadrupole and hexadecapole we find, $D_H(z_{\rm
eff})/r_{\rm drag} = 20.18\pm 0.78$, $D_M(z_{\rm eff})/r_{\rm drag} =17.49 \pm
0.52$ and $f\sigma_8(z_{\rm eff})=0.454\pm0.046$. We combine both sets of
results along with the measurements in configuration space of \cite{LRG_corr}
and report the following consensus values: $D_H(z_{\rm eff})/r_{\rm drag} =
19.77\pm 0.47$, $D_M(z_{\rm eff})/r_{\rm drag} = 17.65\pm 0.30$ and
$f\sigma_8(z_{\rm eff})=0.473\pm 0.044$, which are in full agreement with the
standard $\Lambda$CDM and GR predictions. These results represent the most
precise measurements within the redshift range $0.6\leq z \leq 1.0$ and are the
culmination of more than 8 years of SDSS observations. |
Cosmic Clocks: In a perturbed Universe, comoving tracers on a two-dimensional surface of
constant observed redshift are at different proper time since the Big Bang. For
tracers whose age is known independently, one can measure these perturbations
of the proper time. Examples of such sources include cosmic events which only
happen during a short period of cosmic history, as well as evolving standard
candles and standard rulers. In this paper we derive a general gauge-invariant
linear expression for this perturbation in terms of space-time perturbations.
As an example, we show that the observed temperature perturbations of the
cosmic microwave background (CMB) on large scales are exactly given by these
proper time perturbations. Together with the six ruler perturbations derived in
Schmidt and Jeong (2012), this completes the set of independent observables
which can be measured with standard rulers and candles. | Microlensing and dynamical constraints on primordial black hole dark
matter with an extended mass function: The recent discovery of gravitational waves from mergers of $\sim 10 \,
M_{\odot}$ black hole binaries has stimulated interested in Primordial Black
Hole dark matter in this mass range. Microlensing and dynamical constraints
exclude all of the dark matter being in compact objects with a delta function
mass function in the range $10^{-7} \lesssim M/ M_{\odot} \lesssim 10^{5}$.
However it has been argued that all of the dark matter could be composed of
compact objects in this range with an extended mass function. We explicitly
recalculate the microlensing and dynamical constraints for compact objects with
an extended mass function which replicates the PBH mass function produced by
inflation models. We find that the microlensing and dynamical constraints place
conflicting constraints on the width of the mass function, and do not find a
mass function which satisfies both constraints. |
Systematic effects in large-scale angular power spectra of photometric
quasars and implications for constraining primordial nongaussianity: Primordial non-Gaussianity of local type is predicted to lead to enhanced
halo clustering on very large scales. Photometric quasars, which can be seen
from cosmological redshifts z>2 even in wide-shallow optical surveys, are
promising tracers for constraining non-Gaussianity using this effect. However,
large-scale systematics can also mimic this signature of non-Gaussianity. In
order to assess the contribution of systematic effects, we cross-correlate
overdensity maps of photometric quasars from the Sloan Digital Sky Survey
(SDSS) Data Release 6 (DR6) in different redshift ranges. We find that the maps
are significantly correlated on large scales, even though we expect the angular
distributions of quasars at different redshifts to be uncorrelated. This
implies that the quasar maps are contaminated with systematic errors. We
investigate the use of external templates that provide information on the
spatial dependence of potential systematic errors to reduce the level of
spurious clustering in the quasar data. We find that templates associated with
stellar density, the stellar color locus, airmass, and seeing are major
contaminants of the quasar maps, with seeing having the largest effect. Using
template projection, we are able to decrease the significance of the
cross-correlation measurement on the largest scales from 9.2-sigma to
5.4-sigma. Although this is an improvement, the remaining cross-correlation
suggests the contamination in this quasar sample is too great to allow a
competitive constraint on fNL by correlations internal to this sample. The SDSS
quasar catalog exhibits spurious number density fluctuations of ~2% rms, and we
need a contamination level less than 1% (0.6%) in order to measure values of
fNL less than 100 (10). Properly dealing with these systematics will be
paramount for future large scale structure surveys that seek to constrain
non-Gaussianity. | Observational constraints on running vacuum model: We investigate the power spectra of the CMB temperature and matter density in
the running vacuum model (RVM) with the time-dependent cosmological constant of
$\Lambda = 3 \nu H^2 + \Lambda_0$, where $H$ is the Hubble parameter. In this
model, dark energy decreases in time and decays to both matter and radiation.
By using the Markov chain Monte Carlo method, we constrain the model parameter
$\nu$ as well as the cosmological observables. Explicitly, we obtain $\nu \leq
1.54 \times 10^{-4}$ (68\% confidence level) in the RVM with the best-fit
$\chi^2_{\mathrm{RVM}} = 13968.8$, which is slightly smaller than
$\chi^2_{\Lambda \mathrm{CDM}} = 13969.8$ in the $\Lambda$CDM model of $\nu=0$. |
LoCuSS: First Results from Strong-lensing Analysis of 20 Massive Galaxy
Clusters at z~0.2: We present a statistical analysis of a sample of 20 strong lensing clusters
drawn from the Local Cluster Substructure Survey (LoCuSS), based on high
resolution Hubble Space Telescope imaging of the cluster cores and follow-up
spectroscopic observations using the Keck-I telescope. We use detailed
parameterized models of the mass distribution in the cluster cores, to measure
the total cluster mass and fraction of that mass associated with substructures
within R<250kpc.These measurements are compared with the distribution of
baryons in the cores, as traced by the old stellar populations and the X-ray
emitting intracluster medium. Our main results include: (i) the distribution of
Einstein radii is log-normal, with a peak and 1sigma width of
<log(RE(z=2))>=1.16+/-0.28; (ii) we detect an X-ray/lensing mass discrepancy of
<M_SL/M_X>=1.3 at 3 sigma significance -- clusters with larger substructure
fractions displaying greater mass discrepancies, and thus greater departures
from hydrostatic equilibrium; (iii) cluster substructure fraction is also
correlated with the slope of the gas density profile on small scales, implying
a connection between cluster-cluster mergers and gas cooling. Overall our
results are consistent with the view that cluster-cluster mergers play a
prominent role in shaping the properties of cluster cores, in particular
causing departures from hydrostatic equilibrium, and possibly disturbing cool
cores. Our results do not support recent claims that large Einstein radius
clusters present a challenge to the CDM paradigm. | Accelerating universe and the time-dependent fine-structure constant: Theoretical background of our proposed relation between the accelerating
universe and the time-variability of the fine-structure constant is discussed,
based on the scalar-tensor theory, with emphases on the intuitive aspects of
underlying physical principles. An important comment is added on the successful
understanding of the size of the effective cosmological constant responsible
for the acceleration, without appealing to fine-tuning parameters. |
Stellar Populations of UV-Selected Active Galactic Nuclei Host Galaxies
at z ~ 2 - 3: We use stellar population synthesis modeling to analyze the host galaxy
properties of a sample of 33 UV-selected, narrow-lined active galactic nuclei
(AGNs) at z ~ 2 - 3. In order to quantify the contribution of AGN emission to
host galaxy broadband spectral energy distributions (SEDs), we use the
subsample of 11 AGNs with photometric coverage spanning from rest-frame UV
through near-IR wavelengths. Modeling the SEDs of these objects with a linear
combination of stellar population and AGN templates, we infer the effect of the
AGN on derived stellar population parameters. We also estimate the typical bias
in derived stellar populations for AGNs lacking rest-frame near-IR wavelength
coverage, and develop a method for inferring the true host galaxy properties.
We compare AGN host galaxy properties to those of a sample of UV-selected,
star-forming non-AGNs in the same redshift range, including a subsample
carefully matched in stellar mass. Although the AGNs have higher masses and
SFRs than the full non-active sample, their stellar population properties are
consistent with those of the mass-selected sample, suggesting that the presence
of an AGN is not connected with the cessation of star-formation activity in
star-forming galaxies at z ~ 2 - 3. We suggest that a correlation between M_BH
and galaxy stellar mass is already in place at this epoch. Assuming a roughly
constant Eddington ratio for AGNs at all stellar masses, we are unable to
detect the AGNs in low-mass galaxies because they are simply too faint. | Molecular and atomic line surveys of galaxies II: unbiased estimates of
their star formation mode: We make use of our 'minimal' cold interstellar medium (ISM) emission line
model that predicts the molecular and atomic line emission per unit dense,
star-forming gas mass (Geach & Papadopoulos 2012; Paper I) to examine the
utility of key line ratios in surveys of the so-called star formation 'mode' as
traced by xi_SF = M_dense(H_2)/M_total(H_2). We argue that xi_SF and its
proxies provide very sensitive, extinction-free discriminators of rapid
starburst/merger-driven versus secular quiescent/disk-like stellar mass
assembly, with the most promising diagnostic to be applied in the near-future
being CO(4-3)/[CI](1-0). These lines are accessible across nearly the full
range 0<z<2 (thus covering the bulk of galaxy evolution) with the Atacama Large
Millimeter Array. In addition to their diagnostic power, another advantage of
this combination is the similar observed frequencies (Delta nu_0 ~ 30 GHz) of
the lines, resulting in nearly spatially-matched beams for a fixed aperture,
thus mitigating the effects of resolution/morphology bias in the interpretation
of galaxy-averaged line ratios. Finally we discuss the capability of deep blind
redshift surveys with the high frequency component of the Square Kilometer
Arrray (SKA) in discovering H_2-rich galaxies with very low xi_SF values. These
could be the progenitors of starburst galaxies seen prior to the onset of star
formation; such galaxies could be a class of extreme outliers from local (gas
surface density)-(star formation rate) scaling laws, which would exclude them
from current star formatation or stellar mass selected samples. Our
conservative model suggests that SKA could detect such systems residing at z~3
at a rate of 20-200 per hour. |
UV Extinction Towards a Quiescent Molecular Cloud in the SMC: Context: The mean UV extinction law for the Small Magellanic Cloud (SMC) is
usually taken as a template for low-metallicity galaxies. However, its current
derivation is based on only five stars, thus placing doubts on its
universality. An increase in the number of targets with measured extinction
laws in the SMC is necessary to determine its possible dependence on parameters
such as metallicity and star-forming activity. Aims: To measure the UV
extinction law for several stars in the quiescent molecular cloud SMC B1-1.
Methods: We obtained HST/STIS slitless UV spectroscopy of a 25"x25" field of
view and we combined it with ground-based NIR and visible photometry of the
stars in the field. The results were processed using the Bayesian photometric
package CHORIZOS to derive the visible-NIR extinction values for each star. The
unextinguished Spectral Energy Distributions (SEDs) obtained in this way were
then used to derive the UV extinction law for the four most extinguished stars.
We also recalculated the visible-NIR extinction for the five SMC stars with
preexisting UV extinction laws. Results: The UV extinction law for four SMC
B1-1 stars within several pc of each other differs significantly from star to
star. The 2175 {\AA} bump is moderately strong in one, weak in two, and absent
in the fourth. | Phase Space Distribution Functions and Energy Distributions of Dark
Matter Particles in Haloes: We calculate the phase space distribution function (DF) and the energy
distribution of dark matter particles for a spherical halo in dynamical
equilibrium assuming the Navarro-Frenk-White (NFW) density profile. Comparing
the results with simulations of a wide range of haloes, we find that with
appropriate matching, the energy distribution for a simulated halo can be well
described by that derived from the best-fit NFW profile. Deviations occur at
low energy when the NFW profile provides a poor fit for $r<0.05R_{vir}$, where
$R_{vir}$ is the virial radius. The comparisons of DFs are similar to those of
energy distributions, but the DF derived from the best-fit NFW profile has
somewhat less accuracy because additional deviations are introduced through the
density of energy states. We also compare the NFW fits to the simulated DFs and
energy distributions with the DarkEXP fits of Hjorth & Williams
(arXiv:1010.0265). We find that these fits have comparable accuracy in the
region where both fit well, and that there is an approximate relation between
the energy scale of the DarkEXP fits and the parameters of the NFW profile. The
DarkEXP fits are better at low energy because they require the central
gravitational potential as an input. |
An X-ray view of quasars: I present an overview of observational studies of quasars of all types, with
particular emphasis on X-ray observational studies. The presentation is based
on the most popularly accepted unified picture of quasars - collectively
referred to as AGN (active galactic nuclei) in this review. Characteristics of
X-ray spectra and X-ray variability obtained from various X-ray satellites over
the last 5 decades have been presented and discussed. The contribution of AGN
in understanding the cosmic X-ray background is discussed very briefly. Attempt
has been made to provide up-to-date information; however, this is a vast
subject and this presentation is not intended to be comprehensive. | A Clustered Extragalactic Foreground Model for the EoR: We review an improved statistical model of extra-galactic point-source
foregrounds first introduced in [Murray 2017], in the context of the Epoch of
Reionization. This model extends the instrumentally-convolved foreground
covariance used in inverse-covariance foreground mitigation schemes, by
considering the cosmological clustering of the sources. In this short work, we
show that over scales of $k \sim (0.6, 40.) h {\rm Mpc}^{-1}$, ignoring source
clustering is a valid approximation. This is in contrast to [Murray 2017], who
found a possibility of false detection if the clustering was ignored. The
dominant cause for this change is the introduction of a Galactic synchrotron
component which shadows the clustering of sources. |
Interaction between dark energy and dark matter: observational
constraints from OHD, BAO, CMB and SNe Ia: In order to test if there is energy transfer between dark energy and dark
matter, we investigate cosmological constraints on two forms of nontrivial
interaction between the dark matter sector and the sector responsible for the
acceleration of the universe, in light of the newly revised observations
including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies
for both phenomenological forms of the interaction term $Q=3\gamma H\rho$,
i.e., the parameter $\gamma$ to be a small number, $|\gamma|\approx 10^{-2}$.
However, concerning the sign of the interaction parameter, we observe that
$\gamma>0$ when the interaction between dark sectors is proportional to the
energy density of dust matter, whereas the negative coupling ($\gamma<0$) is
preferred by observations when the interaction term is proportional to dark
energy density. We further discuss two possible explanations to this
incompatibility and apply a quantitative criteria to judge the severity of the
coincidence problem. Results suggest that the $\gamma_m$IDE model with a
positive coupling may alleviate the coincidence problem, since its coincidence
index $C$ is smaller than that for the $\gamma_d$IDE model, the interacting
quintessence and phantom models by four orders of magnitude. | Evidence for the kinematic Sunyaev-Zeľdovich effect with ACTPol and
velocity reconstruction from BOSS: We use microwave temperature maps from two seasons of data from the Atacama
Cosmology Telescope (ACTPol) at 146 GHz, together with the Constant Mass CMASS
galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the
kinematic Sunyaev-Ze\v{l}dovich (kSZ) effect over the redshift range z = 0.4 -
0.7. We use galaxy positions and the continuity equation to obtain a
reconstruction of the line-of-sight velocity field. We stack the cosmic
microwave background temperature at the location of each halo, weighted by the
corresponding reconstructed velocity. The resulting best fit kSZ model is
preferred over the no-kSZ hypothesis at 3.3sigma and 2.9sigma for two
independent velocity reconstruction methods, using 25,537 galaxies over 660
square degrees. The effect of foregrounds that are uncorrelated with the galaxy
velocities is expected to be well below our signal, and residual thermal
Sunyaev-Ze\v{l}dovich contamination is controlled by masking the most massive
clusters. Finally, we discuss the systematics involved in converting our
measurement of the kSZ amplitude into the mean free electron fraction of the
halos in our sample. |
Merger Shocks in Abell 3667 and the Cygnus~A Cluster: We present new XMM-Newton observations of the northwest (NW) radio relic
region in the cluster Abell 3667. We detect a jump in the X-ray surface
brightness and X-ray temperature at the sharp outer edge of the radio relic
which indicate that this is the location of a merger shock with a Mach number
of about 2. Comparing the radio emission to the shock properties implies that
approximately 0.2% of the dissipated shock kinetic energy goes into
accelerating relativistic electrons. This is an order of magnitude smaller than
the efficiency of shock acceleration in many Galactic supernova remnants, which
may be due to the lower Mach numbers of cluster merger shocks. The X-ray and
radio properties indicate that the magnetic field strength in the radio relic
is >= 3 muG, which is a very large field at a projected distance of ~2.2 Mpc
from the center of a cluster. The radio spectrum is relatively flat at the
shock, and steepens dramatically with distance behind the shock. This is
consistent with radiative losses by the electrons and the post-shock speed
determined from the X-ray properties. The Cygnus A radio source is located in a
merging cluster of galaxies. This appears to be an early-stage merger. Our
recent Suzaku observation confirm the presence of a hot region between the two
subclusters which agrees with the predicted shocked region. The high spectral
resolution of the CCDs on Suzaku allowed us to measure the radial component of
the merger velocity, Delta v_r \approx 2650 km/s. | Optically faint X-ray sources in the CDFN: Spitzer constraints: We investigate the properties of the most optically faint sources in the
GOODS-N area (R > 26.5 AB). Such extremely optically faint populations present
an uncharted territory despite the fact that they represent an appreciable
fraction of the X-ray sources in the GOODS-N field. They are believed to
contain either red AGN at moderate redshifts or possibly QSO at very high
redshift. We compile our sample by first finding the 3.6um IRAC counterparts of
the X-ray sources and searching for the optical counterparts of the IRAC
sources. 35 sources do not have counterparts in the R-band Subaru optical
images. Of these, 18 have HST-ACS counterparts while the remaining have no
optical counterparts. The vast majority of our 35 sources are classified as
Extremely Red Objects (EROs) on the basis of their V-K lower limits. Their
photometric redshifts show that these populate moderate redshifts (median
z~2.8), being markedly different from the already spectroscopically identified
population which peaks at z~0.7. The Spitzer-IRAC mid-IR colours of the sources
which have no HST counterparts tend to lie within the mid-IR colour diagram AGN
"wedge", suggesting either QSO, ULIRG (Mrk231), or early-type galaxy templates
at z>3. A large fraction of our sources (17/35), regardless of whether they
have HST counterparts, can be classified as mid-IR bright/optically faint
sources (Dust Obscured Galaxies) a class which is believed to include many
heavily absorbed AGN. The co-added X-ray spectrum of the optically faint
sources is very flat having a spectral index of Gamma~0.87, significantly
flatter than the spectrum of the X-ray background. The optically faint R>26.5
X-ray sources constitute more than 50% of the total X-ray population at
redshifts z>2 bearing important implications for the luminosity function and
its evolution; considering X-ray sources with 2<z<4 we find good agreement with
a modified PLE model. |
One never walks alone: the effect of the perturber population on subhalo
measurements in strong gravitational lenses: Analyses of extended arcs in strong gravitational lensing images to date have
constrained the properties of dark matter by measuring the parameters of one or
two individual subhalos. However, since such analyses are reliant on
likelihood-based methods like Markov-chain Monte Carlo or nested sampling, they
require various compromises to the realism of lensing models for the sake of
computational tractability, such as ignoring the numerous other subhalos and
line-of-sight halos in the system, assuming a particular form for the source
model and requiring the noise to have a known likelihood function. Here we show
that a simulation-based inference method called truncated marginal neural ratio
estimation (TMNRE) makes it possible to relax these requirements by training
neural networks to directly compute marginal posteriors for subhalo parameters
from lensing images. By performing a set of inference tasks on mock data, we
verify the accuracy of TMNRE and show it can compute posteriors for subhalo
parameters marginalized over populations of hundreds of subhalos and
line-of-sight halos, as well as lens and source uncertainties. We also find the
MLP Mixer network works far better for such tasks than the convolutional
architectures explored in other lensing analyses. Furthermore, we show that
since TMNRE learns a posterior function it enables direct statistical checks
that would be extremely expensive with likelihood-based methods. Our results
show that TMNRE is well-suited for analyzing complex lensing data, and that the
full subhalo and line-of-sight halo population must be included when measuring
the properties of individual dark matter substructures. | Baryon-Interacting Dark Matter: heating dark matter and the emergence of
galaxy scaling relations: The empirical scaling relations observed in disk galaxies remain challenging
for models of galaxy formation. The most striking among these is the Mass
Discrepancy-Acceleration Relation (MDAR), which encodes both a tight baryonic
Tully-Fisher relation (BTFR) and the observed diversity of galaxy rotation
curves through the central surface density relation (CSDR). Building on our
earlier work, we propose here that the MDAR is the result of interactions
between baryons and 'Baryon-Interacting Dark Matter' (BIDM), which heat up the
dark matter. Following a bottom-up, hydrodynamical approach, we find that the
MDAR follows if: $i)$ the BIDM equation of state approximates that of an ideal
gas; $ii)$ the BIDM relaxation time is order the Jeans time; $iii)$ the heating
rate is inversely proportional to the BIDM density. Remarkably, under these
assumptions the set of hydrodynamical equations together with Poisson's
equation enjoy an anisotropic scaling symmetry. In the BIDM-dominated regime,
this gives rise to an enhanced symmetry which fully captures the
low-acceleration limit of the MDAR. We then show that, assuming a cored
pseudo-isothermal profile at equilibrium, this set of equations gives rise to
parameters reproducing the MDAR. Specifically, in the flat part of the rotation
curve the asymptotic rotational velocity matches the parametric dependence of
the BTFR. Moreover, in the central region of high-surface brightness galaxies,
the profile reproduces the CSDR. Finally, by studying the time-dependent
approach to equilibrium, we derive a global combination of the BTFR and CSDR,
which matches the expectations in low surface-brightness galaxies. The form of
the heating rate also makes model-independent predictions for various
cosmological observables. We argue that our scenario satisfies existing
observational constraints, and, intriguingly, offers a possible explanation to
the EDGES anomaly. |
Are fast radio bursts generated by cosmic string cusps?: We revisit the idea that cosmic strings could source fast radio bursts by
taking into account Lorentz boosts and a weaker assumption about the scaling
law for the energy of particle decay. We show that the distance relation and
time scale, for a specific value of the scaling of energy, are still compatible
with observations. However, the event rate predicted by the model is too high
when compared to the data. We additionally show that a more realistic string,
with a finite thickness, further compounds the problem by prohibiting cusp
formation and point out how a superconducting wiggly string could circumvent
this issue. | From inflation to dark matter halo profiles: the impact of primordial
non-Gaussianities on the central density cusp: It has recently been shown that local primordial non-Gaussianities (PNG) with
significant amplitude ($|f_{\rm NL}| \sim 1000$), at small (Mpc) scales, can
help in forming simulated galaxies with more disky baryonic kinematics than in
the Gaussian case, while generating matter power spectra that can differ by up
to 20% from the Gaussian case at non-linear scales. Here, we explore in detail
the consequences of such small-scale PNG on the dark matter halo profiles. We
show in particular that, for negative $f_{\rm NL}$, dark matter halos formed in
collisionless simulations are not always well described by the traditional
Navarro-Frenk-White (NFW) profiles, as supported by their sparsity
distribution. We conclude that NFW profiles are not as clear attractors for the
density profiles of dark matter halos in the presence of PNG than in the case
of a Gaussian contrast density field. We show how a minimal extension of the
NFW profile can describe halos both in the Gaussian and non-Gaussian cases.
From the combination of our sparsity analysis and the quality of the
adjustments of the density profiles with a minimal extension to NFW, we
conclude that $z=1$ halos carry the most interesting information about PNG. |
Harmonic analysis of discrete tracers of large-scale structure: It is commonplace in cosmology to analyze fields projected onto the celestial
sphere, and in particular density fields that are defined by a set of points
e.g. galaxies. When performing an harmonic-space analysis of such data (e.g. an
angular power spectrum) using a pixelized map one has to deal with aliasing of
small-scale power and pixel window functions. We compare and contrast the
approaches to this problem taken in the cosmic microwave background and
large-scale structure communities, and advocate for a direct approach that
avoids pixelization. We describe a method for performing a pseudo-spectrum
analysis of a galaxy data set and show that it can be implemented efficiently
using well-known algorithms for special functions that are suited to
acceleration by graphics processing units (GPUs). The method returns the same
spectra as the more traditional map-based approach if in the latter the number
of pixels is taken to be sufficiently large and the mask is well sampled. The
method is readily generalizable to cross-spectra and higher-order functions. It
also provides a convenient route for distributing the information in a galaxy
catalog directly in harmonic space, as a complement to releasing the
configuration-space positions and weights. We make public a code enabling the
application of our method to existing and upcoming datasets. | Gaussian processes and effective field theory of $f(T)$ gravity under
the $H_0$ tension: We consider the effective field theory formulation of torsional gravity in a
cosmological framework to alter the background evolution. Then we use the
latest $H_0$ measurement from the SH0ES Team as well as observational Hubble
data from cosmic chronometer (CC) and radial baryon acoustic oscillations (BAO)
and we reconstruct the $f(T)$ form in a model-independent way by applying
Gaussian processes. Since the special square-root term does not affect the
evolution at the background level, we finally summarize a family of functions
that can produce the background evolution required by the data. Lastly,
performing a fitting using polynomial functions, and implementing the Bayesian
Information Criterion (BIC), we find an analytic expression that may describe
the cosmological evolution in great agreement with observations. |
Constraining neutrino mass and dark energy with peculiar velocities and
lensing dispersions of Type Ia supernovae: We show that peculiar velocities of Type Ia supernovae can be used to derive
constraints on the sum of neutrino masses, $\Sigma m_{\nu}$, and dark energy
equation of state, $w = w_0+w_a(1-a)$, from measurements of the
magnitude-redshift relation, complementary to galaxy redshift and weak lensing
surveys. Light from a supernova propagates through a perturbed Universe so the
luminosity distance is modified from its homogeneous prediction. This
modification is proportional to the matter density fluctuation and its time
derivative due to gravitational lensing and peculiar velocity respectively. At
low redshifts, the peculiar velocity signal dominates while at high redshifts
lensing does. We show that using lensing and peculiar velocity of supernovae
from the upcoming surveys WFIRST and ZTF, without other observations, we can
constrain $\Sigma m_{\nu} \lesssim 0.31$ eV, $\sigma(w_0) \lesssim 0.02$, and
${\sigma(w_a)} \lesssim 0.18$ ($1-\sigma$ CL) in the $\Sigma
m_{\nu}$-$w_0$-$w_a$ parameter space, where all the other cosmological
parameters are fixed. We find that adding peculiar velocity information from
low redshifts shrinks the volume of the parameter ellipsoid in this space by
$\sim 33$%. We also allow $\Omega_{\text{CDM}}$ to vary as well as $\Sigma
m_{\nu}$, $w_0$ and $w_a$, and demonstrate how these constraints degrade as a
consequence. | A Neural Network Gravitational Arc Finder based on the Mediatrix
filamentation Method: Automated arc detection methods are needed to scan the ongoing and
next-generation wide-field imaging surveys, which are expected to contain
thousands of strong lensing systems. Arc finders are also required for a
quantitative comparison between predictions and observations of arc abundance.
Several algorithms have been proposed to this end, but machine learning methods
have remained as a relatively unexplored step in the arc finding process. In
this work we introduce a new arc finder based on pattern recognition, which
uses a set of morphological measurements derived from the Mediatrix
Filamentation Method as entries to an Artificial Neural Network (ANN). We show
a full example of the application of the arc finder, first training and
validating the ANN on simulated arcs and then applying the code on four Hubble
Space Telescope (HST) images of strong lensing systems. The simulated arcs use
simple prescriptions for the lens and the source, while mimicking HST
observational conditions. We also consider a sample of objects from HST images
with no arcs in the training of the ANN classification. We use the training and
validation process to determine a suitable set of ANN configurations, including
the combination of inputs from the Mediatrix method, so as to maximize the
completeness while keeping the false positives low. In the simulations the
method was able to achieve a completeness of about 90% with respect to the arcs
that are input to the ANN after a preselection. However, this completeness
drops to $\sim$ 70% on the HST images. The false detections are of the order of
3% of the objects detected in these images. The combination of Mediatrix
measurements with an ANN is a promising tool for the pattern recognition phase
of arc finding. More realistic simulations and a larger set of real systems are
needed for a better training and assessment of the efficiency of the method. |
Correlation functions for extended mass galaxy clusters: The phenomenon of clustering of galaxies on the basis of correlation
functions in an expanding Universe is studied by using equation of state,
taking gravitational interaction between galaxies of extended nature into
consideration. The partial differential equation for the extended mass
structures of a two-point correlation function developed earlier by Iqbal,
Ahmad and Khan is studied on the basis of assigned boundary conditions. The
solution for the correlation function for extended structures satisfies the
basic boundary conditions, which seem to be sufficient for understanding the
phenomena, and provides a new insight into the gravitational clustering problem
for extended mass structures. | Accurate emulator for the redshift-space power spectrum of dark matter
halos and its application to galaxy power spectrum: An accurate theoretical template of the redshift-space galaxy power spectrum,
if applicable out to nonlinear scales, enables us to extract more stringent and
robust constraints on cosmological parameters from the measured galaxy
clustering. In this work, we develop a simulation-based template, so-called
emulator, for the redshift-space power spectrum of dark matter halos. Using the
redshift-space halo power spectra measured from the Dark Quest $N$-body
simulation suite that covers 101 flat-geometry $w$CDM cosmologies around the
Planck $\Lambda$CDM model, we feed these data into a feed-forward neural
network to build the fast and accurate emulation of the power spectrum from the
linear to nonlinear scales up to $k \simeq 0.6 \,h \,{\rm Mpc}^{-1}$. Our
emulator achieves about 1% and 5% fractional accuracies in predicting the
monopole and quadrupole moments of the power spectrum, respectively, for halos
of $\sim 10^{13}h^{-1}M_\odot$ that correspond to host halos of the SDSS LOWZ-
and CMASS-like galaxies, where the achieved accuracies are sufficient compared
to the statistical errors of SDSS volume. The validation and performance of the
emulator are given by the comparison of the emulator predictions with the power
spectra directly measured from the simulations for validation sets that are not
used in the training. We demonstrate that the emulator outputs can be used to
make model predictions for the redshift-space power spectrum of galaxies by
employing user-fed models for the halo-galaxy connection, such as the halo
occupation distribution. The emulator allows us to easily incorporate the
Finger-of-God effect due to the virial motions of galaxies and the
Alcock-Paczy\'{n}ski distortions. Our code can compute the redshift-space
galaxy power spectrum in a CPU subseconds and is ready to perform the
emulator-based cosmological analysis for the exiting and upcoming galaxy
redshift surveys. |
Non-Halo Structures and their Effects on Gravitational Lensing: Anomalies in the flux-ratios of the images of quadruply-lensed quasars have
been used to constrain the nature of dark matter. Assuming these lensing
perturbations are caused by dark matter haloes, it is currently possible to
constrain the mass of a hypothetical Warm Dark Matter (WDM) particle to be
$m_\chi > 5.2$ keV. However, the assumption that perturbations are only caused
by DM haloes might not be correct as other structures, such as filaments and
pancakes, exist and make up a significant fraction of the mass in the universe,
ranging between 5$\%$ -- 50$\%$ depending on the dark matter model. Using novel
fragmentation-free simulations of 1 and 3keV WDM cosmologies we study these
"non-halo" structures and estimate their impact on flux-ratio observations. We
find that these structures display sharp density gradients with short
correlation lengths, and can contribute more to the lensing signal than all
haloes up to the half-mode mass combined, thus reducing the differences
expected among WDM models. We estimate that non-halo structures can be the
dominant cause of line-of-sight flux-ratio anomalies in very warm, but already
excluded, $m_x \sim 1 \rm{keV}$ scenarios. For colder cases $m_x \gtrsim 3
\rm{keV}$, we estimate that non-haloes can contribute about $5 - 10\%$ of the
total flux-ratio signal. | The DiskMass Survey. VI. Gas and stellar kinematics in spiral galaxies
from PPak integral-field spectroscopy: We present ionized-gas (OIII) and stellar kinematics (velocities and velocity
dispersions) for 30 nearly face-on spiral galaxies out to as much as three disk
scale lengths (h_R). These data have been derived from PPak IFU spectroscopy
(4980-5370A), observed at a mean resolution of R=7700 (sigma_inst=17km/s).
These data are a fundamental product of our survey and will be used in
companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of
each galaxy in our sample. Our presentation provides a comprehensive
description of the observing strategy, data reduction, and analysis. Along with
a clear presentation of the data, we demonstrate: (1) The OIII and stellar
rotation curves exhibit a clear signature of asymmetric drift with a rotation
difference that is 11% of the maximum rotation speed of the galaxy disk,
comparable to measurements in the solar neighborhood in the Milky Way. (2) The
e-folding length of the stellar velocity dispersion is two times h_R on
average, as expected for a disk with a constant scale height and mass-to-light
ratio, with a scatter that is notably smaller for massive,
high-surface-brightness disks in the most luminous galaxies. (3) At radii
larger than 1.5 h_R, the stellar velocity dispersion tends to decline slower
than the best-fitting exponential function, which may be due to an increase in
the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter
halo. (4) A strong correlation exists between the central vertical stellar
velocity dispersion of the disks and their circular rotational speed at 2.2
h_R, with a zero point indicating that galaxy disks are submaximal. Moreover,
weak but consistent correlations exist such that disks with a fainter central
surface brightness in bluer and less luminous galaxies of later morphological
types are kinematically colder with respect to their rotational velocities. |
Spectral Classification and Redshift Measurement for the SDSS-III Baryon
Oscillation Spectroscopic Survey: (abridged) We describe the automated spectral classification, redshift
determination, and parameter measurement pipeline in use for the Baryon
Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III
(SDSS-III) as of Data Release 9, encompassing 831,000 moderate-resolution
optical spectra. We give a review of the algorithms employed, and describe the
changes to the pipeline that have been implemented for BOSS relative to
previous SDSS-I/II versions, including new sets of stellar, galaxy, and quasar
redshift templates. For the color-selected CMASS sample of massive galaxies at
redshift 0.4 <~ z <~ 0.8 targeted by BOSS for the purposes of large-scale
cosmological measurements, the pipeline achieves an automated classification
success rate of 98.7% and confirms 95.4% of unique CMASS targets as galaxies
(with the balance being mostly M stars). Based on visual inspections of a
subset of BOSS galaxies, we find that ~0.2% of confidently reported CMASS
sample classifications and redshifts are incorrect, and ~0.4% of all CMASS
spectra are objects unclassified by the current algorithm which are potentially
recoverable. The BOSS pipeline confirms that ~51.5% of the quasar targets have
quasar spectra, with the balance mainly consisting of stars. Statistical (as
opposed to systematic) redshift errors propagated from photon noise are
typically a few tens of km/s for both galaxies and quasars, with a significant
tail to a few hundreds of km/s for quasars. We test the accuracy of these
statistical redshift error estimates using repeat observations, finding them
underestimated by a factor of 1.19 to 1.34 for galaxies, and by a factor of 2
for quasars. We assess the impact of sky-subtraction quality, S/N, and other
factors on galaxy redshift success. Finally, we document known issues, and
describe directions of ongoing development. | An improved upper limit to the CMB circular polarization at large
angular scales: Circular polarization of the Cosmic Microwave Background (CMB) offers the
possibility of detecting rotations of the universe and magnetic fields in the
primeval universe or in distant clusters of galaxies. We used the Milano
Polarimeter (MIPOL) installed at the Testa Grigia Observatory, on the italian
Alps, to improve the existing upper limits to the CMB circular polarization at
large angular scales. We obtain 95% confidence level upper limits to the degree
of the CMB circular polarization ranging between 5.0x10^{-4} and 0.7x10^{-4} at
angular scales between 8 and 24 deg, improving by one order of magnitude
preexisting upper limits at large angular scales. Our results are still far
from the nK region where today expectations place the amplitude of the V Stokes
parameter used to characterize circular polarization of the CMB but improve the
preexisting limit at similar angular scales. Our observations offered also the
opportunity of characterizing the atmospheric emission at 33 GHz at the Testa
Grigia Observatory. |
The red-sequence of 72 WINGS local galaxy clusters: We study the color-magnitude red sequence and blue fraction of 72 X-ray
selected galaxy clusters at z=0.04-0.07 from the WINGS survey, searching for
correlations between the characteristics of the red sequence and the
environment. We consider the slope and scatter of the red sequence, the number
ratio of red luminous-to-faint galaxies, the blue fraction and the fractions of
ellipticals, S0s and spirals that compose the red sequence. None of these
quantities correlate with the cluster velocity dispersion, X-ray luminosity,
number of cluster substructures, BCG prevalence over next brightest galaxies
and spatial concentration of ellipticals. Instead, the properties of the red
sequence depend strongly on local galaxy density. Higher density regions have a
lower RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and
a lower spiral fraction on the RS. Our results highlight the prominent effect
of the local density in setting the epoch when galaxies become passive and join
the red sequence, as opposed to the mass of the galaxy host structure. | Light Dark Matter Search Using a Diamond Cryogenic Detector: Diamond operated as a cryogenic calorimeter is an excellent target for direct
detection of low-mass dark matter candidates. Following the realization of the
first low-threshold cryogenic detector that uses diamond as absorber for
astroparticle physics applications, we now present the resulting exclusion
limits on the elastic spin-independent interaction cross-section of dark matter
with diamond. We measured two 0.175 g CVD (Chemical Vapor Deposition) diamond
samples, each instrumented with a W-TES. Thanks to the energy threshold of just
16.8 eV of one of the two detectors, we set exclusion limits on the elastic
spin-independent interaction of dark matter particles with carbon nuclei down
to dark matter masses as low as 0.122 GeV/c2. This work shows the scientific
potential of cryogenic detectors made from diamond and lays the foundation for
the use of this material as target for direct detection dark matter
experiments. |
Spectroscopic Constraints on the Form of the Stellar Cluster Mass
Function: This contribution addresses the question of whether the initial cluster mass
function (ICMF) has a fundamental limit (or truncation) at high masses. The
shape of the ICMF at high masses can be studied using the most massive young
(<10 Myr) clusters, however this has proven difficult due to low-number
statistics. In this contribution we use an alternative method based on the
luminosities of the brightest clusters, combined with their ages. If a
truncation is present, a generic prediction (nearly independent of the cluster
disruption law adopted) is that the median age of bright clusters should be
younger than that of fainter clusters. In the case of an non-truncated ICMF,
the median age should be independent of cluster luminosity. Here, we present
optical spectroscopy of twelve young stellar clusters in the face-on spiral
galaxy NGC 2997. The spectra are used to estimate the age of each cluster, and
the brightness of the clusters is taken from the literature. The observations
are compared with the model expectations of Larsen (2009) for various ICMF
forms and both mass dependent and mass independent cluster disruption. While
there exists some degeneracy between the truncation mass and the amount of mass
independent disruption, the observations favour a truncated ICMF. For low or
modest amounts of mass independent disruption, a truncation mass of 5-6*10^5
Msun is estimated, consistent with previous determinations. Additionally, we
investigate possible truncations in the ICMF in the spiral galaxy M83, the
interacting Antennae galaxies, and the collection of spiral and dwarf galaxies
present in Larsen (2009) based on photometric catalogues taken from the
literature, and find that all catalogues are consistent with having a
(environmentally dependent) truncation in the cluster mass functions. | Brane inflation and the robustness of the Starobinsky inflationary model: The first inflationary model conceived was the one proposed by Starobinsky
which includes an additional term quadratic in the Ricci-scalar R in the
Einstein-Hilbert action. The model is now considered a target for several
future cosmic microwave background experiments given its compatibility with
current observational data. In this paper, we analyse the robustness of the
Starobinsky inflation by inserting it into a generalized scenario based on a
$\beta$-Starobinsky inflation potential, which is motivated through brane
inflation. In the Einstein frame, the generalized model recovers the original
model for $\beta=0$, whereas $\forall \beta \neq 0$ represents an extended
class of models that admit a wider range of solutions. We investigate limits on
$\beta$ from current cosmic microwave background and baryonic acoustic
oscillation data and find that only a small deviation from the original
scenario is allowed, $\beta=-0.08 \pm 0.12$ (68% C.L.), which is fully
compatible with zero and confirms the robustness of the Starobinsky
inflationary model in light of current observations. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.