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Rotation Speed of the First Stars: We estimate the rotation speed of Population III (Pop III) stars within a
minihalo at z ~ 20 using a smoothed particle hydrodynamics (SPH) simulation,
beginning from cosmological initial conditions. We follow the evolution of the
primordial gas up to densities of 10^12 cm^-3. Representing the growing
hydrostatic cores with accreting sink particles, we measure the velocities and
angular momenta of all particles that fall onto these protostellar regions.
This allows us to record the angular momentum of the sinks and estimate the
rotational velocity of the Pop III stars expected to form within them. The
rotation rate has important implications for the evolution of the star, the
fate encountered at the end of its life, and the potential for triggering a
gamma-ray burst (GRB). We find that there is sufficient angular momentum to
yield rapidly rotating stars (> 1000 km s^-1, or near break-up speeds). This
indicates that Pop III stars likely experienced strong rotational mixing,
impacting their structure and nucleosynthetic yields. A subset of them was also
likely to result in hypernova explosions, and possibly GRBs. | Probing primordial non-Gaussianity with the power spectrum and
bispectrum of future 21cm intensity maps: After reionisation, the 21cm emission line of neutral hydrogen within
galaxies provides a tracer of dark matter. Next-generation intensity mapping
surveys, with the SKA and other radio telescopes, will cover large sky areas
and a wide range of redshifts, facilitating their use as probes of primordial
non-Gaussianity. {Previous works have shown that the bispectrum can achieve
tight constraints on primordial non-Gaussianity with future surveys that are
purposely designed for intensity mapping in interferometer mode}. Here we
investigate the constraints attainable from surveys operating in single-dish
mode, \rev{using the combined power spectrum and bispectrum signal}. In the
case of the power spectrum, single-dish surveys typically outperform
interferometer surveys. We find that the reverse holds for the bispectrum:
single-dish surveys are not competitive with surveys designed for
interferometer mode. |
A Multiphase Absorber Containing O VI and Broad H I Directly Tracing
10^6 K Plasma at Low-Redshift Toward HE 0153-4520: Observations of the QSO HE 0153-4520 (z-em = 0.450) with the Cosmic Origins
Spectrograph (COS) from 1134 to 1796 A with a resolution of ~17 km/s and
signal-to- noise per resolution element of 20 to 40 are used to study a
multi-phase partial Lyman limit system (LLS) at z = 0.22601 tracing both cool
and hot gas. FUSE observations of the Lyman limit break yield log N(H I) =
16.61(0.12, -0.17) The observed UV absorption lines of H I 1216 to 926, C III,
C II, N III, N II, Si III, and Si II imply the existence of cool photoionized
gas in the LLS with log U = -2.8\pm0.1 and log N(H) = 19.35\pm0.18, log n(H) =
-2.9\pm0.2, log T = 4.27\pm0.02, log (P/k) = 1.75\pm0.17, and log L(kpc) =
0.70\pm0.25. The abundances are [X/H] = -0.8 (+0.3, -0.2) for N, Si and C but
the result is sensitive to the assumed shape of the ionizing background
radiation field. The multi-phase system has strong O VI and associated broad Ly
{\alpha} absorption (BLA) with log N(O VI) = 14.21\pm0.02, b(O VI) = 37\pm1
km/s, log N(H I) = 13.70(+0.05,-0.08), b(H I)=140 (+14, -16) km/s and b(H
I)/b(O VI) = 3.9\pm0.4. The O VI does not arise in the cool photoionized gas of
the LLS. The O VI and BLA imply the direct detection of thermally broadened
absorption by hot gas with log T = 6.07 (+0.09, -0.12), [O/H] = -0.28 (+0.09,
-0.08), and log N(H) = 20.41 (+0.13, -0.17). The absorber probably occurs in
the circumgalactic environment (halo) of a foreground galaxy. | The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31
Halo with Blue Horizontal Branch Stars: We attempt to constrain the shape of M31's inner stellar halo by tracing the
surface density of blue horizontal branch (BHB) stars at galactocentric
distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved
stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury
(PHAT) survey, supplemented by several archival Hubble Space Telescope
observations. We find that the ratio of BHB to red giant stars is relatively
constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of
the halo population as the red giant branch. In the inner halo, we do not
expect BHB stars to be produced by the high metallicity bulge and disk, making
BHB stars a good candidate to be a reliable tracer of the stellar halo to much
smaller galactocentric distances. If we assume a power-law profile r^(-\alpha)
for the 2-D projected surface density BHB distribution, we obtain a
high-quality fit with a 2-D power-law index of \alpha=2.6^{+0.3}_{-0.2} outside
of 3 kpc, which flattens to \alpha<1.2 inside of 3 kpc. This slope is
consistent with previous measurements but is anchored to a radial baseline that
extends much farther inward. Finally, assuming azimuthal symmetry and a
constant mass-to-light ratio, the best-fitting profile yields a total halo
stellar mass of 2.1^{+1.7}_{-0.4} x 10^9 M_sun. These properties are comparable
with both simulations of stellar halo formation formed by satellite disruption
alone, and with simulations that include some in situ formation of halo stars. |
Sandage-Loeb test for the new agegraphic and Ricci dark energy models: The Sandage-Loeb (SL) test is a unique method to explore dark energy at the
``redshift desert'' ($2\lesssim z\lesssim 5$), an era not covered by any other
dark energy probes, by directly measuring the temporal variation of the
redshift of quasar (QSO) Lyman-$\alpha$ absorption lines. In this paper, we
study the prospects for constraining the new agegraphic dark energy (NADE)
model and the Ricci dark energy (RDE) model with the SL test. We show that,
assuming only a ten-year survey, the SL test can constrain these two models
with high significance. | The excitation of near-infrared H2 emission in NGC 253: Because of its large angular size and proximity to the Milky Way, NGC 253, an
archetypal starburst galaxy, provides an excellent laboratory to study the
intricacies of this intense episode of star formation. We aim to characterize
the excitation mechanisms driving the emission in NGC 253. Specifically we aim
to distinguish between shock excitation and UV excitation as the dominant
driving mechanism, using Br\gamma, H_2 and [FeII] as diagnostic emission line
tracers. Using SINFONI observations, we create linemaps of Br\gamma,
[FeII]_{1.64}, and all detected H_2 transitions. By using symmetry arguments of
the gas and stellar gas velocity field, we find a kinematic center in agreement
with previous determinations. The ratio of the 2-1 S(1) to 1-0 S(1) H_2
transitions can be used as a diagnostic to discriminate between shock and
fluorescent excitation. Using the 1-0 S(1)/2-1 S(1) line ratio as well as
several other H_2 line ratios and the morphological comparison between H_2 and
Br\gamma and [FeII], we find that excitation from UV photons is the dominant
excitation mechanisms throughout NGC 253. We employ a diagnostic energy level
diagram to quantitatively differentiate between mechanisms. We compare the
observed energy level diagrams to PDR and shock models and find that in most
regions and over the galaxy as a whole, fluorescent excitation is the dominant
mechanism exciting the H_2 gas. We also place an upper limit of the percentage
of shock excited H_2 at 29%. We find that UV radiation is the dominant
excitation mechanism for the H_2 emission. The H_2 emission does not correlate
well with Br\gamma but closely traces the PAH emission, showing that not only
is H_2 fluorescently excited, but it is predominately excited by slightly lower
mass stars than O stars which excite Br\gamma, such as B stars. |
A Study of the Gas-Star Formation Relation over Cosmic Time: We use the first systematic data sets of CO molecular line emission in z~1-3
normal star forming galaxies for a comparison of the dependence of
galaxy-averaged star formation rates on molecular gas masses at low and high
redshifts, and in different galactic environments. Although the current high-z
samples are still small and biased toward the luminous and massive tail of the
actively star-forming 'main-sequence', a fairly clear picture is emerging.
Independent of whether galaxy integrated quantities or surface densities are
considered, low- and high-z SFG galaxy populations appear to follow similar
molecular gas-star formation relations with slopes 1.1 to 1.2. The
gas-depletion time scale in these SFGs grows from 0.5 Gyrs at z~2 to 1.5 Gyrs
at z~0. Because star formation depletion times are significantly smaller than
the Hubble time at all redshifts sampled, star formation rates and gas
fractions are set by the balance between gas accretion from the halo and
stellar feedback. In contrast, very luminous gas rich major mergers at both
low-z and high-z produce on average 4 to10 times more far-infrared luminosity
per unit gas mass. Only some fraction of this difference can be explained by
uncertainties in gas-mass or luminosity estimators; much of it must be
intrinsic. The most likely interpretation is that the star formation relation
is driven by global dynamical effects. For a given mass, the more compact
merger systems produce stars more rapidly because their gas clouds are more
compressed with shorter dynamical times, so that they churn more quickly
through the available gas reservoir than the typical normal disk galaxies. When
the dependence on galactic dynamical time scale is explicitly included, disk
galaxies and mergers appear to follow similar gas to star-formation relations.
The mergers may be forming stars at slightly higher efficiencies than the
disks. | EasyCritics I: Efficient detection of strongly-lensing galaxy groups and
clusters in wide-field surveys: We present EasyCritics, an algorithm to detect strongly-lensing groups and
clusters in wide-field surveys without relying on a direct recognition of arcs.
EasyCritics assumes that light traces mass in order to predict the most likely
locations of critical curves from the observed fluxes of luminous red
early-type galaxies in the line of sight. The positions, redshifts and fluxes
of these galaxies constrain the idealized gravitational lensing potential as a
function of source redshift up to five free parameters, which are calibrated on
few known lenses. From the lensing potential, EasyCritics derives the critical
curves for a given, representative source redshift. The code is highly
parallelized, uses fast Fourier methods and, optionally, GPU acceleration in
order to process large datasets efficiently. The search of a $\smash{1 \,
\mathrm{deg}^2}$ field of view requires less than 1 minute on a modern
quad-core CPU, when using a pixel resolution of $0.25''/\mathrm{px}$. In this
first part of a paper series on EasyCritics, we describe the main underlying
concepts and present a first demonstration on data from the
Canada-France-Hawaii-Telescope Lensing Survey. We show that EasyCritics is able
to identify known group- and cluster-scale lenses, including a cluster with two
giant arc candidates that were previously missed by automated arc detectors. |
Resolved stellar mass maps of galaxies. I: method and implications for
global mass estimates: (Abridged) We introduce a novel technique to construct spatially resolved
maps of stellar mass surface density in galaxies based on optical and near IR
imaging. We use optical/NIR colour(s) to infer effective stellar mass-to-light
ratios (M/L) at each pixel, which are then multiplied by the surface brightness
to obtain the local stellar surface mass density. We build look-up tables to
express M/L as a function of colour(s) by marginalizing over a Monte Carlo
library of 50,000 stellar population synthesis (SPS) models by Charlot &
Bruzual (2007), which include a revised prescription for the TP-AGB stellar
evolutionary phase, with a wide range of dust exinctions. In order to extract
reliable flux and colour information at any position in the galaxy, we perform
a median adaptive smoothing of the images that preserves the highest possible
spatial resolution. As the most practical and robust, and hence fiducial
method, we express the M/L in the H band as a function of (g-i) and (i-H).
Stellar mass maps computed in this way have a typical accuracy of 30 per cent
or less at any given pixel, determined from the scatter in the models. We
compare maps obtained with our fiducial method with those derived using other
combinations of bandpasses and the old BC03 TP-AGB prescription. Finally, we
compare total stellar mass estimates obtained by integrating resolved mass maps
with those obtained with unresolved photometry. In galaxies with evident dust
lanes, unresolved estimates may miss up to 40 per cent of the total stellar
mass because dusty regions are strongly under-represented in the luminous
fluxes. | Evidence for cosmological particle creation?: A joint analysis of the linear matter power spectrum, distance measurements
from type Ia supernovae and the position of the first peak in the anisotropy
spectrum of the cosmic microwave background indicates a cosmological, late-time
dark matter creation at 95% confidence level. |
BASILISK: Bayesian Hierarchical Inference of the Galaxy-Halo Connection
using Satellite Kinematics--I. Method and Validation: We present a Bayesian hierarchical inference formalism (Basilisk) to
constrain the galaxy-halo connection using satellite kinematics. Unlike
traditional methods, Basilisk does not resort to stacking the kinematics of
satellite galaxies in bins of central luminosity, and does not make use of
summary statistics, such as satellite velocity dispersion. Rather, Basilisk
leaves the data in its raw form and computes the corresponding likelihood. In
addition, Basilisk can be applied to flux-limited, rather than volume-limited
samples, greatly enhancing the quantity and dynamic range of the data. And
finally, Basilisk is the only available method that simultaneously solves for
halo mass and orbital anisotropy of the satellite galaxies, while properly
accounting for scatter in the galaxy-halo connection. Basilisk uses the
conditional luminosity function to model halo occupation statistics, and
assumes that satellite galaxies are a relaxed tracer population of the host
halo's potential with kinematics that obey the spherical Jeans equation. We
test and validate Basilisk using mocks of varying complexity, and demonstrate
that it yields unbiased constraints on the galaxy-halo connection and at a
precision that rivals galaxy-galaxy lensing. In particular, Basilisk accurately
recovers the full PDF of the relation between halo mass and central galaxy
luminosity, and simultaneously constrains the orbital anisotropy of the
satellite galaxies. Basilisk's inference is not affected by potential velocity
bias of the central galaxies, or by slight errors in the inferred, radial
profile of satellite galaxies that arise as a consequence of interlopers and
sample impurity. | The zoo plot meets the swampland: mutual (in)consistency of single-field
inflation, string conjectures, and cosmological data: We consider single-field inflation in light of string-motivated "swampland"
conjectures suggesting that effective scalar field theories with a consistent
UV completion must have field excursion $\Delta \phi \lesssim M_{\rm Pl}$, in
combination with a sufficiently steep potential, $M_{\rm Pl} V_\phi/V \gtrsim
{\cal O}(1)$. Here, we show that the swampland conjectures are inconsistent
with existing observational constraints on single-field inflation. Focusing on
the observationally favoured class of concave potentials, we map the allowed
swampland region onto the $n_S$-$r$ "zoo plot" of inflationary models, and find
that consistency with the Planck satellite and BICEP2/Keck Array requires
$M_{\rm Pl} V_\phi/V \lesssim 0.1$ and $-0.02 \lesssim M_{\rm Pl}^2
V_{\phi\phi}/V < 0$, in strong tension with swampland conjectures. Extension to
non-canonical models such as DBI Inflation does not significantly weaken the
bound. |
Conservative cosmology: combining data with allowance for unknown
systematics: When combining data sets to perform parameter inference, the results will be
unreliable if there are unknown systematics in data or models. Here we
introduce a flexible methodology, BACCUS: BAyesian Conservative Constraints and
Unknown Systematics, which deals in a conservative way with the problem of data
combination, for any degree of tension between experiments. We introduce
hyperparameters that describe a bias in each model parameter for each class of
experiments. A conservative posterior for the model parameters is then obtained
by marginalization both over these unknown shifts and over the width of their
prior. We contrast this approach with an existing hyperparameter method in
which each individual likelihood is scaled, comparing the performance of each
approach and their combination in application to some idealized models. Using
only these rescaling hyperparameters is not a suitable approach for the current
observational situation, in which internal null tests of the errors are passed,
and yet different experiments prefer models that are in poor agreement. The
possible existence of large shift systematics cannot be constrained with a
small number of data sets, leading to extended tails on the conservative
posterior distributions. We illustrate our method with the case of the $H_0$
tension between results from the cosmic distance ladder and physical
measurements that rely on the standard cosmological model. | A Maximum Likelihood Analysis of Low-Energy CDMS Data: An unbinned maximum likelihood analysis of CDMS low-energy data reveals a
strong preference (5.7 sigma C.L.) for a model containing an exponential excess
of events in the nuclear recoil band, when compared to the null hypothesis. We
comment on the possible origin of such an excess, establishing a comparison
with anomalies in other dark matter experiments. A recent annual modulation
search in CDMS data is shown to be insufficiently sensitive to test a dark
matter origin for this excess. |
Investigating Cosmological GAN Emulators Using Latent Space
Interpolation: Generative adversarial networks (GANs) have been recently applied as a novel
emulation technique for large scale structure simulations. Recent results show
that GANs can be used as a fast, efficient and computationally cheap emulator
for producing novel weak lensing convergence maps as well as cosmic web data in
2-D and 3-D. However, like any algorithm, the GAN approach comes with a set of
limitations, such as an unstable training procedure and the inherent randomness
of the produced outputs. In this work we employ a number of techniques commonly
used in the machine learning literature to address the mentioned limitations.
In particular, we train a GAN to produce both weak lensing convergence maps and
dark matter overdensity field data for multiple redshifts, cosmological
parameters and modified gravity models. In addition, we train a GAN using the
newest Illustris data to emulate dark matter, gas and internal energy
distribution data simultaneously. Finally, we apply the technique of latent
space interpolation to control which outputs the algorithm produces. Our
results indicate a 1-20% difference between the power spectra of the
GAN-produced and the training data samples depending on the dataset used and
whether Gaussian smoothing was applied. Finally, recent research on generative
models suggests that such algorithms can be treated as mappings from a
lower-dimensional input (latent) space to a higher dimensional (data) manifold.
We explore such a theoretical description as a tool for better understanding
the latent space interpolation procedure. | Baryons at the Edge of the X-ray Brightest Galaxy Cluster: Studies of the diffuse X-ray emitting gas in galaxy clusters have provided
powerful constraints on cosmological parameters and insights into plasma
astrophysics. However, measurements of the faint cluster outskirts have become
possible only recently. Using data from the Suzaku X-ray telescope, we
determined an accurate, spatially resolved census of the gas, metals, and dark
matter out to the edge of the Perseus Cluster. Contrary to previous results,
our measurements of the cluster baryon fraction are consistent with the
expected universal value at half of the virial radius. The apparent baryon
fraction exceeds the cosmic mean at larger radii, suggesting a clumpy
distribution of the gas, which is important for understanding the ongoing
growth of clusters from the surrounding cosmic web. |
Self similarity of the dark matter dominated objects and the shape of
small scale power spectrum: We analyzed available observational data of a sample of dark matter (DM)
dominated galaxies and clusters of galaxies and we have found correlations
between the virial mass, $M_{vir}$, of halos and basic parameters of their
cores, namely, the mean DM density, pressure and entropy. These correlations
are a natural consequence of similar evolution of all such objects. It is
driven mainly by gravitational interactions what implies a high degree of self
similarity of both the process of halos formation and their internal structure.
We confirmed the CDM--like shape of both the small and large scale power
spectrum. However, our reconstruction of the evolutionary history of observed
objects requires either a multicomponent composition of DM or a more complex
primordial power spectrum of density perturbations with significant excess of
power at scales of clusters of galaxies and larger. We demonstrated that a
model with suitable combination of the heavy DM particles (CDM) and DM
particles with large damping scale (HDM) could provide a successful description
of the observational data in a wide range of masses. | The Evolution of the Intracluster Medium Metallicity in
Sunyaev-Zel'dovich-Selected Galaxy Clusters at 0 < z < 1.5: We present the results of an X-ray spectral analysis of 153 galaxy clusters
observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These
clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected
sample of galaxy clusters discovered in the 2500 square degree South Pole
Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure
time of 9.1 Ms, these data yield the strongest constraints to date on the
evolution of the metal content of the intracluster medium (ICM). We find no
evidence for strong evolution in the global (r<R500) ICM metallicity (dZ/dz =
-0.06 +/- 0.04 Zsun), with a mean value at z=0.6 of <Z> = 0.23 +/- 0.01 Zsun
and a scatter of 0.08 +/- 0.01 Zsun. These results imply that >60% of the
metals in the ICM were already in place at z=1 (at 95% confidence), consistent
with the picture of an early (z>1) enrichment. We find, in agreement with
previous works, a significantly higher mean value for the metallicity in the
centers of cool core clusters versus non-cool core clusters. We find weak
evidence for evolution in the central metallicity of cool core clusters (dZ/dz
= -0.21 +/- 0.11 Zsun), which is sufficient to account for this enhanced
central metallicity over the past ~10 Gyr. We find no evidence for metallicity
evolution outside of the core (dZ/dz = -0.03 +/- 0.06 Zsun), and no significant
difference in the core-excised metallicity between cool core and non-cool core
clusters. This suggests that strong radio-mode AGN feedback does not
significantly alter the distribution of metals at r>0.15R500. Given the
limitations of current-generation X-ray telescopes in constraining the ICM
metallicity at z>1, significant improvements on this work will likely require
next-generation X-ray missions. |
Attention-Based Neural Network Emulators for Multi-Probe Data Vectors
Part II: Assessing Tension Metrics: The next generation of cosmological surveys is expected to generate
unprecedented high-quality data, consequently increasing the already
substantial computational costs of Bayesian statistical methods. This will pose
a significant challenge to analyzing theoretical models of cosmology.
Additionally, new mitigation techniques of baryonic effects, intrinsic
alignment, and other systematic effects will inevitably introduce more
parameters, slowing down the convergence of Bayesian analyses. In this
scenario, machine-learning-based accelerators are a promising solution, capable
of reducing the computational costs and execution time of such tools by order
of thousands. Yet, they have not been able to provide accurate predictions over
the wide prior ranges in parameter space adopted by Stage III/IV collaborations
in studies employing real-space two-point correlation functions. This paper
offers a leap in this direction by carefully investigating the modern
transformer-based neural network (NN) architectures in realistic simulated
Rubin Observatory year one cosmic shear $\Lambda$CDM inferences. Building on
the framework introduced in Part I, we generalize the transformer block and
incorporate additional layer types to develop a more versatile architecture. We
present a scalable method to efficiently generate an extensive training dataset
that significantly exceeds the scope of prior volumes considered in Part I,
while still meeting strict accuracy standards. Through our meticulous
architecture comparison and comprehensive hyperparameter optimization, we
establish that the attention-based architecture performs an order of magnitude
better in accuracy than widely adopted NN designs. Finally, we test and apply
our emulators to calibrate tension metrics. | Cosmography with Supernova Refsdal through time-delay cluster lensing:
independent measurements of the Hubble constant and geometry of the Universe: We present new measurements of the values of the Hubble constant, matter
density, dark energy density, and dark energy density equation-of-state
parameters from a full strong lensing analysis of the observed positions of 89
multiple images and 4 measured time delays of SN Refsdal multiple images in the
Hubble Frontier Fields galaxy cluster MACS J1149.5+2223. By strictly following
the identical modelling methodology as in our previous work, that was done
before the time delays were available, our cosmographic measurements here are
essentially blind based on the frozen procedure. Without using any priors from
other cosmological experiments, in an open $w$CDM cosmological model, through
our reference cluster mass model, we measure the following values: $H_0 =
65.1^{+3.5}_{-3.4}$ km s$^{-1}$ Mpc$^{-1}$, $\Omega_{\rm
DE}=0.76^{+0.15}_{-0.10}$, and $w=-0.92^{+0.15}_{-0.21}$ (at the 68.3%
confidence level). No other single cosmological probe is able to measure
simultaneously all these parameters. Remarkably, our estimated values of the
cosmological parameters, particularly $H_0$, are very robust and do not depend
significantly on the assumed cosmological model and the cluster mass modelling
details. The latter introduce systematic uncertainties on the values of $H_0$
and $w$ which are found largely subdominant compared to the statistical errors.
The results of this study show that time delays in lens galaxy clusters,
combined with extensive photometric and spectroscopic information, offers a
novel and competitive cosmological tool. |
Galaxy clusters at high redshift and evolution of brightest cluster
galaxies: Identification of high redshift clusters is important for studies of
cosmology and cluster evolution. Using photometric redshifts of galaxies, we
identify 631 clusters from the Canada-France-Hawaii Telescope (CFHT) Wide
field, 202 clusters from the CHFT Deep field, 187 clusters from the Cosmic
Evolution Survey (COSMOS) and 737 clusters from the Spitzer Wide-area InfraRed
Extragalactic survey (SWIRE) field. The redshifts of these clusters are in the
range of 0.1<z<1.6. Merging these cluster samples gives 1644 clusters in the
four survey fields, of which 1088 are newly identified and more than half are
from the large SWIRE field. Among 228 clusters of z>1, 191 clusters are newly
identified, and most of them from the SWIRE field. With this large sample of
high redshift clusters, we study the color evolution of the brightest cluster
galaxies (BCGs). The colors r'-z' and r^+-m_{3.6\mu m} of the BCGs are
consistent with a stellar population synthesis model in which the BCGs are
formed at redshift z_f>2 and evolved passively. The colors g'-z' and
B-m_{3.6\mu m} of the BCGs at redshifts z>0.8 are systematically bluer than the
passive evolution model for galaxy formed at z_f~2, indicating star formation
in high redshift BCGs. | A New Picture of Cosmic String Evolution and Anisotropic Stochastic
Gravitational-Wave Background: We investigate the anisotropies of the stochastic gravitational-wave
background (SGWB) produced by cosmic strings associated with the spontaneous
U(1) symmetry breaking of Grand Unified Theory, which happens at the onset of
inflation. The string network evolution is determined by primordial
fluctuations and never reaches the scaling regime. The string loops are
inhomogeneously distributed in large scale regions, resulting in large
anisotropies in the SGWB. We find that the angular power spectrum of SGWB
anisotropies depends on frequency, which is testable in multiband observations
of GWs. In particular, GWs from the cosmic strings can appropriately interpret
the common-spectrum process reported by NANOGrav collaboration, and the angular
power spectrum in the nanohertz band,
$\mathtt{l}(\mathtt{l}+1)C_{\mathtt{l}}=5.6\times 10^{-2}$ at large scales, is
expected to be detectable by pulsar timing array experiments in the near
future. |
A cool dark sector, concordance, and a low $σ_8$: We investigate a cosmological model in which a fraction of the dark matter is
atomic dark matter (ADM). This ADM consists of dark versions of the electron
and of the proton, interacting with each other and with dark photons just as
their light sector versions do, but interacting with everything else only
gravitationally. We find constraints given current cosmic microwave background
(CMB) and baryon acoustic oscillation (BAO) data, with and without an $H_0$
prior, and with and without enforcing a big bang nucleosynthesis consistent
helium abundance. We find that, at low dark photon temperature, one can have
consistency with BAO and CMB data, with a fraction of dark matter that is ADM
($f_{\rm adm}$) as large as $\sim 0.1$. Such a large $f_{\rm adm}$ leads to a
suppression of density fluctuations today on scales below about 60 Mpc that may
be of relevance to the $\sigma_8$ tension. Our work motivates calculation of
nonlinear corrections to matter power spectrum predictions in the ADM model. We
forecast parameter constraints to come from future ground-based CMB surveys,
and find that if ADM is indeed the cause of the $\sigma_8$ tension, the
influence of the ADM, primarily on CMB lensing, will likely be detectable at
high significance. | Redshift drift in a pressure-gradient cosmology: We derive a redshift drift formula for the spherically symmetric
inhomogeneous pressure Stephani universes which are complementary to the
spherically symmetric inhomogeneous density Lema\^itre-Tolman-Bondi models. We
show that there is a clear difference between redshift drift predictions for
these two models as well as between the Stephani models and the standard
$\Lambda$CDM Friedmann models. The Stephani models have positive drift values
at small redshift and behave qualitatively (but not quantitatively) as the
$\Lambda$CDM models at large redshift, while the drift for LTB models is always
negative. This prediction may perhaps be tested in future telescopes such as
European Extremely Large Telescope (EELT), Thirty Meter Telescope (TMT), Giant
Magellan Telescope (GMT), and especially, in gravitational wave interferometers
DECi-Hertz Interferometer Gravitational Wave Observatory and Big Bang Observer
(DECIGO/BBO), which aim at low redshift. |
On Estimating Lyman-alpha Forest Correlations between Multiple
Sightlines: The next frontier of Lyman-alpha forest studies is the reconstruction of 3D
correlations from a dense sample of background sources. The measurement of 3D
correlations has the potential to improve constraints on fundamental
cosmological parameters, ionizing background models, and the reionization
history. This study addresses the sensitivity of spectroscopic surveys to 3D
correlations in the Lyman-alpha forest. We show that the sensitivity of a
survey to this signal can be quantified by just a single number, a
noise-weighted number density of sources on the sky. We investigate how the
sensitivity of a spectroscopic quasar (or galaxy) survey scales as a function
of its depth, area, and redshift. We propose a simple method for weighting
sightlines with varying S/N levels to estimate the correlation function, and we
show that this estimator generally performs nearly as well as the minimum
variance quadratic estimator. In addition, we show that the sensitivity of a
quasar survey to the flux correlation function is generally maximized if it
observes each field just long enough to achieve S/N ~ 2 in a 1 A pixel on an
L_* quasar while acquiring spectra for all quasars with L > L_*: Little is
gained by integrating longer on the same targets or by including fainter
quasars. We quantify how these considerations relate to constraints on the
angular diameter distance, the curvature of space-time, and the reionization
history. | Running vacuum in the Universe: phenomenological status in light of the
latest observations, and its impact on the $σ_8$ and $H_0$ tensions: A substantial body of phenomenological and theoretical work over the last few
years strengthens the possibility that the vacuum energy density (VED) of the
universe is dynamical, and in particular that it adopts the `running vacuum
model' (RVM) form, in which the VED evolves mildly as $\delta \rho_{\rm
vac}(H)\sim \nu_{\rm eff} m_{\rm Pl}^2{\cal O}\left(H^2\right)$, where $H$ is
the Hubble rate and $\nu_{\rm eff}$ is a (small) free parameter. This dynamical
scenario is grounded on recent studies of quantum field theory (QFT) in curved
spacetime and also on string theory. It turns out that what we call the
`cosmological constant', $\Lambda$, is no longer a rigid parameter but the
nearly sustained value of $8\pi G(H)\rho_{\rm vac}(H)$ around (any) given epoch
$H(t)$, where $G(H)$ is the gravitational coupling, which can also be very
mildly running (logarithmically). Of particular interest is the possibility
suggested in past works that such a running may help to cure the cosmological
tensions afflicting the $\Lambda$CDM. In the current study, we reanalyze it in
full and we find it becomes further buttressed. Using the modern cosmological
data, namely a compilation of the latest $SNIa+BAO+$H(z)$+LSS+CMB$
observations, we probe to which extent the RVM provides a quality fit better
than the concordance $\Lambda$CDM model, paying particular emphasis on its
impact on the $\sigma_8$ and $H_0$ tensions. We utilize the Einstein-Boltzmann
system solver $CLASS$ and the Monte Carlo sampler $MontePython$ for the
statistical analysis, as well as the statistical $DIC$ criterion to compare the
running vacuum against the rigid vacuum ($\nu_{\rm eff} = 0$). We show that
with a tiny amount of vacuum dynamics ($|\nu_{\rm eff}|\ll 1$) the global fit
can improve significantly with respect to the $\Lambda$CDM and the mentioned
tensions may subside to inconspicuous levels. |
A candle in the wind: a radio filament in the core of the A3562 galaxy
cluster: Using a MeerKAT observation of the galaxy cluster A3562 (a member of the
Shapley Supercluster), we have discovered a narrow, long and straight, very
faint radio filament, which branches out at a straight angle from the tail of a
radio galaxy located in projection near the core of the cluster. The radio
filament spans 200 kpc and aligns with a sloshing cold front seen in the
X-rays, staying inside the front in projection. The radio spectral index along
the filament appears uniform (within large uncertainties) at $\alpha\simeq
-1.5$. We propose that the radio galaxy is located outside the cold front, but
dips its tail under the front. The tangential wind that blows there may stretch
the radio plasma from the radio galaxy into a filamentary structure. Some
reacceleration is needed in this scenario to maintain the radio spectrum
uniform. Alternatively, the cosmic ray electrons from that spot in the tail can
spread along the cluster magnetic field lines, straightened by that same
tangential flow, via anomalously fast diffusion. Our radio filament can provide
constraints on this process. We also uncover a compact radio source at the
Brightest Cluster Galaxy (BCG) that is 2--3 orders of magnitude less luminous
than those in typical cluster central galaxies -- probably an example of a BCG
starved of accretion fuel by gas sloshing. | Extragalactic Background Light: a measurement at 400 nm using dark cloud
shadow I. Low surface brightness spectrophotometry in the area of Lynds 1642: We present the method and observations for the measurement of the
Extragalactic Background Light (EBL) utilizing the shadowing effect of a dark
cloud. We measure the surface brightness difference between the opaque cloud
core and its unobscured surroundings. In the difference the large atmospheric
and Zodiacal light components are eliminated and the only remaining foreground
component is the scattered starlight from the cloud itself. Although much
smaller, its separation is the key problem in the method. For its separation we
use spectroscopy. While the scattered starlight has the characteristic
Fraunhofer lines and 400 nm discontinuity the EBL spectrum is smooth and
without these features. Medium resolution spectrophotometry at $\lambda$ = 380
- 580 nm was performed with ${VLT}$/FORS at ESO of the surface brightness in
and around the high-galactic-latitude dark cloud Lynds 1642. Besides the
spectrum for the core with $A_V \ge 15$ mag, further spectra were obtained for
intermediate-opacity cloud positions. They are used as proxy for the spectrum
of the impinging starlight spectrum and facilitate the separation of the
scattered starlight (cf. Paper II, Mattila et al. 2017b). Our spectra reach a
precision of $\sim 0.5$ $10^{-9}$ erg cm$^{-2}$s$^{-1}$sr$^{-1}$\AA$^{-1}$ as
required to measure an EBL intensity in range of $\sim$1 to a few times
$10^{-9}$ erg cm$^{-2}$s$^{-1}$sr$^{-1}$\AA$^{-1}$. Because all surface
brightness components are measured using the same equipment the method does not
require unusually high absolute calibration accuracy, a condition which has
been a problem for some previous EBL projects |
Reflection-dominated nuclear X-ray emission in the early-type galaxy ESO
565--G019: We present the discovery of a reflection-dominated active galactic nucleus
(AGN) in the early-type radio-quiet galaxy ESO 565--G019 with Suzaku and
Swift/BAT. The source X-ray spectrum below 10 keV is characteristic of other
Compton-thick (CT) AGN, clearly showing an inverted continuum and prodigious
fluorescence iron emission above ~3 keV. A Compton shoulder to the neutral Fe
Kalpha line also appears to be present. There is evidence for long-term hard
X-ray flux variability which we associate with changes in the intrinsic AGN
power-law. The increasing sensitivity of ongoing and new hard X-ray surveys
means that more such reflection-dominated AGN ought to be uncovered in the near
future. ESO 565--G019 is hosted in an early-type galaxy whose morphology has
been variously classified as either type E or type S0. Only about 20 bona fide
CT-AGN have been identified in the local universe so far, and all exist in host
galaxies with late Hubble types (S0 or later). CT columns of nuclear obscuring
gas are uncommon in early-type galaxies in the local universe, so confirmation
of the exact morphological class of ESO 565--G019 is important. Infrared
photometry also shows the presence of large quantities of cool dust in the
host, indicative of significant ongoing star-formation. ESO 565--G019 may be
the first identified local example of minor-merger driven CT-AGN growth in an
early-type host, or may be the result of interaction with its neighboring
galaxy ESO 565--G018 in a wide pair. | Dark Energy, with Signatures: We propose a class of simple dark energy models which predict a late-time
dark radiation component and a distinctive time-dependent equation of state
$w(z)$ for redshift $z < 3$. The dark energy field can be coupled strongly
enough to Standard Model particles to be detected in colliders, and the model
requires only modest additional particle content and little or no fine-tuning
other than a new energy scale of order milli-electron volts. |
Mapping the temperature of the intra-cluster medium with the tSZ effect: The hot electrons in the intra-cluster medium produce a spectral distorsion
of the cosmic microwave background (CMB) black body emission, the thermal
Sunyaev-Zel'dovich effect (tSZ). This characteristic spectral distorsion is now
commonly used to detect and characterize the properties of galaxy clusters. The
tSZ effect spectral distorsion does not depends on the redshift, and is only
slightly affected by the galaxy cluster properties via the relativistic
corrections, when the electrons reach relativistic velocities. The present work
proposes a linear component separation approach to extract the tSZ effect
Compton parameter and relativistic corrections for next-generation CMB
experiments. We demonstrated that relativistic corrections, if neglected, would
induce a significant bias on galaxy cluster Compton parameter, tSZ scaling
relation slope, and tSZ angular power spectrum shape measurements. We showed
that tSZ relativistic corrections mapping can be achieved at high
signal-to-noise ratio with a low level of contamination up to $\ell=3000$ for
next generation CMB experiments. At smaller angular scales the contamination
produced by infra-red emission will be a significant source of bias. Such tSZ
relativistic corrections mapping enables the study of galaxy cluster
temperature profile via the tSZ effect only. | An Accurate Analytic Model for the Thermal Sunyaev-Zel'dovich One-Point
PDF: Non-Gaussian statistics of late-time cosmological fields contain information
beyond that captured in the power spectrum. Here we focus on one such example:
the one-point probability distribution function (PDF) of the thermal
Sunyaev-Zel'dovich (tSZ) signal in maps of the cosmic microwave background
(CMB). It has been argued that the one-point PDF is a near-optimal statistic
for cosmological constraints from the tSZ signal, as most of the constraining
power in tSZ $N$-point functions is contained in their amplitudes (rather than
their shapes), which probe differently-weighted integrals over the halo mass
function. In this paper, we develop a new analytic halo model for the tSZ PDF,
discarding simplifying assumptions made in earlier versions of this approach.
In particular, we account for effects due to overlaps of the tSZ profiles of
different halos, as well as effects due to the clustering of halos. We verify
the accuracy of our analytic model via comparison to numerical simulations. We
demonstrate that this more accurate model is necessary for the analysis of the
tSZ PDF in upcoming CMB experiments. The novel formalism developed here may be
useful in modeling the one-point PDF of other cosmological observables, such as
the weak lensing convergence field. |
Exploring the Latest Union2 SNIa Dataset by Using Model-Independent
Parametrization Methods: We explore the cosmological consequences of the recently released Union2
sample of 557 Type Ia supernovae (SNIa). Combining this latest SNIa dataset
with the Cosmic microwave background (CMB) anisotropy data from the Wilkinson
Microwave Anisotropy Probe 7 year (WMAP7) observations and the baryon acoustic
oscillation (BAO) results from the Sloan Digital Sky Survey (SDSS) Data Release
7 (DR7), we measure the dark energy density function $f(z)\equiv
\rho_{de}(z)/\rho_{de}(0)$ as a free function of redshift. Two
model-independent parametrization methods (the binned parametrization and the
polynomial interpolation parametrization) are used in this paper. By using the
$\chi^2$ statistic and the Bayesian information criterion, we find that the
current observational data are still too limited to distinguish which
parametrization method is better, and a simple model has advantage in fitting
observational data than a complicated model. Moreover, it is found that all
these parametrizations demonstrate that the Union2 dataset is still consistent
with a cosmological constant at 1$\sigma$ confidence level. Therefore, the
Union2 dataset is different from the Constitution SNIa dataset, which more
favors a dynamical dark energy. | The Lyman-alpha emission of high-z damped Lyman-alpha systems: Using a spectral stacking technique we searched for the average \lya emission
from high-z Damped \lya (DLA) galaxies detected in the Sloan Digital Sky Survey
QSO spectra. We used a sample of 341 DLAs of mean redshift <z>= 2.86 and log
N(HI) > 20.62 to place a 3$\sigma$ upper limit of 3.0 \times 10^{-18} erg
s^{-1} cm^{-2} on the \lya flux emitted within $\sim$1.5 arcsec (or 12 kpc)
from the QSO line of sight. This corresponds to an average \lya luminosity of <
2 \times 10^{41} erg s^{-1} or 0.03 $L_\star$(\lya). This limit is deeper than
the limit of most surveys for faint \lya emitters. The lack of \lya emission in
DLAs is consistent with the in situ star formation, for a given N(HI), being
less efficient than what is seen in local galaxies. Thus, the overall DLA
population seems to originate from the low luminosity end of the high redshift
\lya emitting galaxies and/or to be located far away from the star forming
regions. The latter may well be true since we detect strong OVI absorption in
the stacked spectrum, indicating that DLAs are associated with a highly ionized
phase possibly the relics of galactic winds and/or originating from cold
accretion flows. We find the contribution of DLA galaxies to the global star
formation rate density to be comparatively lower than that of Lyman Break
Galaxies. |
Mixed State Dynamics with Non-Local Interactions: The evolution of degenerate matter out of equilibrium is a topic of interest
in fields such as condensed matter, nuclear and atomic physics, and
increasingly cosmology, including inflaton physics prior to reheating. This
follow-up paper extends the recent paper on the super-de Broglie dynamics of
pure condensates of non-relativistic identical particles subject to non-local
two-body interactions to the dynamics of mixed states. It is found that the
two-body correlation function plays an increasingly dynamical role in these
systems, driving the development of condensates and distributed phases alike.
Examples of distribution and correlation evolution are presented, including
instances of collapse, bound and unbound states, and phonons in the bulk.
Potential applications are also discussed. | Constraints on the dark matter equation of state with redshift-space
distortion: In this paper, we study a model which is composed by the cosmological
constant and dark matter with nonzero equation of state parameter, which could
be called as $\Lambda$wDM. In the synchronous gauge, we obtain the perturbation
equations of dark matter, and deduce the evolution equations of growth factor
about the dark matter and baryons. Based on the Markov Chain Monte Carlo
method, we constrain this model by the recently available cosmic observations
which include cosmic microwave background radiation, baryon acoustic
oscillation, type Ia supernovae, and $f\sigma_8(z)$ data points from
redshift-space distortion. The results present a tighter constraint on the
model than the case without $f\sigma_8(z)$ data. In 3$\sigma$ regions, we find
the dark matter equation of state parameter $w_{dm}$=$0.000111_{-
0.000701-0.00137-0.00180}^{+0.000688+0.00136+0.00181}$. After an extra model
parameter $w_{dm}$ is considered, the difference between the minimum values of
$\chi^2$ of our model and standard model is $\Delta\chi^2_{min}=0.598$.
Although the currently available cosmic observations mildly favor the nonzero
dark matter equation of state parameter, no significant deviation from the
$\Lambda$CDM model is found in 1$\sigma$ region. |
The halo light cone catalogues of \Abacus{AbacusSummit}: We describe a method for generating halo catalogues on the light cone using
the \Abacus{AbacusSummit} suite of $N$-body simulations. The main application
of these catalogues is the construction of realistic mock galaxy catalogues and
weak lensing maps on the sky. Our algorithm associates the haloes from a set of
coarsely-spaced snapshots with their positions at the time of light-cone
crossing by matching halo particles to on-the-fly light cone particles. It then
records the halo and particle information into an easily accessible product,
which we call the \Abacus{AbacusSummit} halo light cone catalogues. Our
recommended use of this product is in the halo mass regime of $M_{\rm halo} >
2.1 \times 10^{11} \ M_\odot/h$ for the \texttt{base} resolution simulations,
i.e. haloes containing at least 100 particles, where the interpolated halo
properties are most reliable. To test the validity of the obtained catalogues,
we perform various visual inspections and consistency checks. In particular, we
construct galaxy mock catalogues of emission-line galaxies (ELGs) at $z \sim 1$
by adopting a modified version of the \Abacus{AbacusHOD} script, which builds
on the standard halo occupation distribution (HOD) method by including various
extensions. We find that the multipoles of the auto-correlation function are
consistent with the predictions from the full-box snapshot, implicitly
validating our algorithm. In addition, we compute and output CMB convergence
maps and find that the auto- and cross-power spectrum agrees with the
theoretical prediction at the subpercent level.
Halo light cone catalogues for 25 \texttt{base} and 2 \texttt{huge}
simulations at the fiducial cosmology is available at
DOI:\href{https://www.doi.org/10.13139/OLCF/1825069}{10.13139/OLCF/1825069} | A large change in the predicted number of small halos due to a small
amplitude oscillating inflaton potential: A smooth inflaton potential is generally assumed when calculating the
primordial power spectrum, implicitly assuming that a very small oscillation in
the inflaton potential creates a negligible change in the predicted halo mass
function. We show that this is not true. We find that a small oscillating
perturbation in the inflaton potential in the slow-roll regime can alter
significantly the predicted number of small halos. A class of models derived
from supergravity theories gives rise to inflaton potentials with a large
number of steps and many transplanckian effects may generate oscillations in
the primordial power spectrum. The potentials we study are the simple quadratic
(chaotic inflation) potential with superimposed small oscillations for small
field values. Without leaving the slow-roll regime, we find that for a wide
choice of parameters, the predicted number of halos change appreciably. For the
oscillations beginning in the 10^7-10^8 solar masses range, for example, we
find that only a 5% change in the amplitude of the chaotic potential causes a
50% suppression of the number of halos for masses between 10^7-10^8 solar
masses and an increase in the number of halos for masses <10^6 solar masses by
factors ~15-50. We suggest that this might be a solution to the problem of the
lack of observed dwarf galaxies in the range 10^7-10^8 solar masses. This might
also be a solution to the reionization problem where a very large number of
Population III stars in low mass halos are required. |
Low redshift AGN in the Hamburg/ESO Survey: I. The local AGN luminosity
function: We present a determination of the local (z=0) luminosity function of
optically selected type 1 (broad-line) Active Galactic Nuclei. Our primary
resource is the Hamburg/ESO Survey (HES), which provides a well-defined sample
of more than 300 optically bright AGN with redshifts z<0.3 and blue magnitudes
B<17.5. AGN luminosities were estimated in two ways, always taking care to
minimise photometric biases due to host galaxy light contamination. Firstly, we
measured broad-band B_J (blue) magnitudes of the objects over small apertures
of the size of the seeing disk. Secondly, we extracted H alpha and H beta broad
emission line luminosities from the spectra which should be entirely free of
any starlight contribution. The resulting AGN luminosity function (AGNLF) is
consistent with a single power law, also when considering the effects of number
density evolution within the narrow redshift range. We compared our AGNLF with
the H alpha luminosity function of lower luminosity Seyfert 1 galaxies by Hao
et al. (2005) and found a smooth transition between both, with excellent
agreement in the overlapping region. From the combination of HES and SDSS
samples we constructed a single local AGNLF spanning more than 4 orders of
magnitude in luminosity. It shows only mild curvature which can be well
described as a double power law with slope indices of -2.0 for the faint end
and -2.8 for the bright end. We predicted the local AGNLF in the soft X-ray
domain and compared this to recent literature data. We also compared the local
AGNLF with results obtained at higher redshifts and find strong evidence for
luminosity-dependent evolution, in the sense that AGN with luminosities around
M_B~-19 are as common in the local universe as they were at z=1.5, supporting
the 'AGN downsizing' picture (abridged). | Tidal interaction vs. ram pressure stripping effects as seen in X-rays.
Hot gas in group and cluster galaxies: The hot intracluster/intragroup medium (ICM/IGM) and a high galaxy density
can lead to perturbations of the galactic interstellar medium (ISM) due to ram
pressure and/or tidal interaction effects. In radio polarimetry observations,
both phenomena may manifest similar features. X-ray data can help to determine
the real origin of the perturbation. We analyse the distribution and physical
properties of the hot gas in the Virgo cluster spiral galaxies NGC 4254 and NGC
4569, which indicate that the cluster environment has had a significant
influence on their properties. By performing both spatial and spectral analyses
of X-ray data, we try to distinguish between two major phenomena: tidal and ram
pressure interactions. We compare our findings with the case of NGC 2276, in
which a shock was reported, by analysing XMM-Newton X-ray data for this galaxy.
We use archival XMM-Newton observations of NGC 4254, NGC 4569, and NGC 2276.
Maps of the soft diffuse emission in the energy band 0.2 - 1 keV are obtained.
For the three galaxies, especially at the position of magnetic field
enhancements we perform a spectral analysis to derive gas temperatures and thus
to look for shock signatures. A shock is a signature of ram pressure resulting
from supersonic velocities; weak tidal interactions are not expected to
influence the temperature of the ionized gas. In NGC 4254, we do not observe
any temperature increase. This suggests tidal interactions rather than ram
pressure stripping. In NGC 4569 the radio polarized ridge shows a higher
temperature, which may indicate ram-pressure effects. For NGC 2276, we do not
find clear indications of a shock. The main driver of the observed distortions
is most likely tidal interaction. Determining gas temperatures via sensitive
X-ray observations seems to be a good method for distinguishing between ram
pressure and tidal interaction effects acting upon a galaxy. |
Inflow of the Broad-Line Region and the Fundamental Limitations of
Reverberation Mapping: The evidence from velocity-resolved reverberation mapping showing a net
infall of the broad-line region (BLR) of AGNs is reviewed. Different lines in
many objects at different epochs give a consistent picture of BLR motions. The
motions are dominated by virialized motion (rotation plus turbulence) with
significant net inflow. The BLR mass influx is sufficient to power the AGN. The
increasing blueshifting of lines with increasing ionization potential is a
consequence of scattering off infalling material. The high blueshiftings of the
UV lines in Narrow-Line Seyfert 1s are due to enhanced BLR inflow rates rather
than strong winds. Seemingly conflicting cases of apparent outflow
reverberation mapping signatures are a result of the breakdown of the
axial-symmetry assumption in reverberation mapping. There are several plausible
causes of this breakdown: high-energy variability tends to be intrinsically
anisotropic, regions of variability are necessarily located off-axis, and X-ray
observations reveal major changes in line-of-sight column densities close to
the black hole. Results from reverberation mapping campaigns dominated by a
single event need to be treated with caution. | The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX
II)\\ II. Construction and Properties of the Survey: Galaxy clusters provide unique laboratories to study astrophysical processes
on large scales and are important probes for cosmology. X-ray observations are
currently the best means of detecting and characterizing galaxy clusters. In
this paper we describe the construction of the REFLEX II galaxy cluster survey
based on the southern part of the ROSAT All-Sky Survey. REFLEX II extends the
REFLEX I survey by a factor of about two down to a flux limit of $1.8 \times
10^{-12}$ erg s$^{-1}$ cm$^{-2}$ (0.1 - 2.4 keV). We describe the determination
of the X-ray parameters, the process of X-ray source identification, and the
construction of the survey selection function. The REFLEX II cluster sample
comprises currently 915 objects. A standard selection function is derived for a
lower source count limit of 20 photons in addition to the flux limit. The
median redshift of the sample is $z = 0.102$. Internal consistency checks and
the comparison to several other galaxy cluster surveys imply that REFLEX II is
better than 90\% complete with a contamination less than 10\%. |
Lensed arc statistics: comparison of Millennium-simulation galaxy
clusters to Hubble Space Telescope observations of an X-ray selected sample: It has been debated for a decade whether there is a large overabundance of
strongly lensed arcs in galaxy clusters, compared to expectations from
LambdaCDM cosmology. We perform ray tracing through the most massive halos of
the Millennium simulation at several redshifts in their evolution, using the
Hubble Ultra Deep Field as a source image, to produce realistic simulated
lensed images. We compare the lensed arc statistics measured from the
simulations to those of a sample of 45 X-ray selected clusters, observed with
the Hubble Space Telescope, that we have analysed in Horesh et al. (2010). The
observations and the simulations are matched in cluster masses, redshifts,
observational effects, and the algorithmic arc detection and selection. At
z=0.6 there are too few massive-enough clusters in the Millennium volume for a
proper statistical comparison with the observations. At redshifts 0.3<z<0.5,
however, we have large numbers of simulated and observed clusters, and the
latter are an unbiased selection from a complete sample. For these redshifts,
we find excellent agreement between the observed and simulated arc statistics,
in terms of the mean number of arcs per cluster, the distribution of number of
arcs per cluster, and the angular separation distribution. At z ~ 0.2 some
conflict remains, with real clusters being ~3 times more efficient arc
producers than their simulated counterparts. This may arise due to selection
biases in the observed subsample at this redshift, to some mismatch in masses
between the observed and simulated clusters, or to physical effects that arise
at low redshift and enhance the lensing efficiency, but which are not
represented by the simulations. | Mapping dark matter on the celestial sphere with weak gravitational
lensing: Convergence maps of the integrated matter distribution are a key science
result from weak gravitational lensing surveys. To date, recovering convergence
maps has been performed using a planar approximation of the celestial sphere.
However, with the increasing area of sky covered by dark energy experiments,
such as Euclid, the Large Synoptic Survey Telescope (LSST), and the Wide Field
Infrared Survey Telescope (WFIRST), this assumption will no longer be valid. We
recover convergence fields on the celestial sphere using an extension of the
Kaiser-Squires estimator to the spherical setting. Through simulations we study
the error introduced by planar approximations. Moreover, we examine how best to
recover convergence maps in the planar setting, considering a variety of
different projections and defining the local rotations that are required when
projecting spin fields such as cosmic shear. For the sky coverages typical of
future surveys, errors introduced by projection effects can be of order tens of
percent, exceeding 50% in some cases. The stereographic projection, which is
conformal and so preserves local angles, is the most effective planar
projection. In any case, these errors can be avoided entirely by recovering
convergence fields directly on the celestial sphere. We apply the spherical
Kaiser-Squires mass-mapping method presented to the public Dark Energy Survey
(DES) science verification data to recover convergence maps directly on the
celestial sphere. |
Luminosity Function from dedicated SDSS-III and MMT data of quasars in
0.7<z<4.0 selected with a new approach: We present a measurement of the quasar luminosity function in the range
0.68<z<4 down to extinction corrected magnitude g_dered=22.5, using a simple
and well understood target selection technique based on the time-variability of
quasars. The completeness of our sample was derived directly from a control
sample of quasars, without requiring complex simulations of quasar light-curves
or colors. A total of 1877 quasar spectra were obtained from dedicated programs
on the Sloan telescope (as part of the SDSS-III/BOSS survey) and on the
Multiple Mirror Telescope. They allowed us to derive the quasar luminosity
function. It agrees well with previously published results in the redshift
range 0.68<z<2.6. Our deeper data allow us to extend the measurement to z=4. We
measured quasar densities to g_dered<22.5, obtaining 30 QSO per deg^2 at z<1,
99 QSO per deg^2 for 1<z<2.15, and 47 QSO per deg^2 at z>2.15. Using pure
luminosity evolution models, we fitted our LF measurements, and predicted
quasar number counts as a function of redshift and observed magnitude. These
predictions are useful inputs for future cosmology surveys such as those
relying on the observation of quasars to measure baryon acoustic oscillations. | Gravitational waves from Affleck-Dine condensate fragmentation: We compute the stochastic gravitational wave production from Affleck-Dine
condensate fragmentation in the early universe, focusing on an effective
potential with a logarithmic mass correction that typically arises in gravity
mediated supersymmetry breaking scenarios. We find that a significant
gravitational wave background can be generated when Q-balls are being formed
out of the condensate fragmentation. This gravitational wave background has a
distinct multi-peak power spectrum where the trough is closely linked to the
supersymmetry breaking scale and whose frequencies are peaked around kHz for
TeV supersymmetry breaking. |
Cluster science from ROSAT to eROSITA: Galaxy clusters are one of the important cosmological probes to test the
consistency of the observable structure and evolution of our Universe with the
predictions of specific cosmological models. We use results from our analysis
of the X-ray flux-limited REFLEX cluster sample from the ROSAT All-Sky Survey
to illustrate the constraints on cosmological parameters that can be achieved
with this approach. The upcoming eROSITA project of the Spektrum-Roentgen-Gamma
mission will increase these capabilities by two orders of magnitude and
importantly also increase the redshift range of such studies. We use the
projected instrument performance to make predictions on the scope of the
eROSITA survey and the potential of its exploitation. | Close Galaxy Pairs at z = 3: A Challenge to UV Luminosity Abundance
Matching: We use a sample of z~3 Lyman Break Galaxies (LBGs) to examine close pair
clustering statistics in comparison to LCDM-based models of structure
formation. Samples are selected by matching the LBG number density and by
matching the observed LBG 3-D correlation function of LBGs over the two-halo
term region. We show that UV-luminosity abundance matching cannot reproduce the
observed data, but if subhalos are chosen to reproduce the observed clustering
of LBGs we are able to reproduce the observed LBG pair fraction, (Nc), defined
as the average number of companions per galaxy. This model suggests an over
abundance of LBGs by a factor of ~5 over those observed, suggesting that only 1
in 5 halos above a fixed mass hosts a galaxy with LBG-like UV luminosity
detectable via LBG selection techniques. We find a total observable close pair
fraction of 23 \pm 0.6% (17.7 \pm 0.5%) using a prototypical cylinder radius in
our overdense fiducial model and 8.3 \pm 0.5% (5.6 \pm 0.2%) in an abundance
matched model (impurity corrected). For the matched spectroscopic slit
analysis, we find Ncs = 5.1\pm0.2% (1.68\pm0.02%), the average number of
companions observed serendipitously in our for fiducial slits (abundance
matched), whereas the observed fraction of serendipitous spectroscopic close
pairs is 4.7\pm1.5 per cent using the full LBG sample and 7.1\pm2.3% for a
subsample with higher signal-to-noise ratio. We show that the standard method
of halo assignment fails to reproduce the break in the LBG close pair behavior
at small scale. To reconcile these discrepancies we suggest that a plausible
fraction of LBGs in close pairs with lower mass than our sample experience
interaction-induced enhanced star formation that boosts their luminosity
sufficiently to be detected in observational sample but are not included in the
abundance matched simulation sample. |
Power spectrum extraction for redshifted 21-cm epoch of reionization
experiments: the LOFAR case: One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization
(EoR) project is to measure the power spectrum of variations in the intensity
of redshifted 21-cm radiation from the EoR. The sensitivity with which this
power spectrum can be estimated depends on the level of thermal noise and
sample variance, and also on the systematic errors arising from the extraction
process, in particular from the subtraction of foreground contamination. We
model the extraction process using realistic simulations of the cosmological
signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR
EoR experiment to the redshifted 21-cm power spectrum. Detection of emission
from the EoR should be possible within 360 hours of observation with a single
station beam. Integrating for longer, and synthesizing multiple station beams
within the primary (tile) beam, then enables us to extract progressively more
accurate estimates of the power at a greater range of scales and redshifts. We
discuss different observational strategies which compromise between depth of
observation, sky coverage and frequency coverage. A plan in which lower
frequencies receive a larger fraction of the time appears to be promising. We
also study the nature of the bias which foreground fitting errors induce on the
inferred power spectrum, and discuss how to reduce and correct for this bias.
The angular and line-of-sight power spectra have different merits in this
respect, and we suggest considering them separately in the analysis of LOFAR
data. | M82 as a Galaxy: Morphology and Stellar Content of the Disk and Halo: For decades, the nuclear starburst has taken all the limelight in M82 with
very little discussion on M82 as a galaxy. The situation is changing over the
last decade, with the publication of some important results on the morphology
and stellar content of its disk and halo. In this review, we discuss these
recent findings in the framework of M82 as a galaxy. It is known for almost
half a century that M82 as a galaxy doesn't follow the trends expected for
normal galaxies that had prompted the morphologists to introduce a separate
morphological type under the name Irr II or amorphous. It is now being
understood that the main reasons behind its apparently distinct morphological
appearance are its peculiar star formation history, radial distribution of gas
density and the form of the rotation curve. The disk formed almost all of its
stars through a burst mode around 500 Myr ago, with the disk star formation
completely quenched around 100 Myr ago. The fossil record of the disk-wide
burst lies in the form of hundreds of compact star clusters, similar in mass to
that of the globular clusters in the Milky Way, but an order of magnitude
younger. The present star formation is restricted entirely to the central 500
pc zone, that contains more than 200 young compact star clusters. The disk
contains a non-star-forming spiral arm, hidden from the optical view by a
combination of extinction and high inclination to the line of sight. The halo
of M82 is also unusual in its stellar content, with evidence for star
formation, albeit at low levels, occurring continuously for over a gigayear. We
carefully examine each of the observed abnormality to investigate the overall
effect of interaction on the evolution of M82. |
Halo Zeldovich model and perturbation theory: dark matter power spectrum
and correlation function: Perturbation theory for dark matter clustering has received a lot of
attention in recent years, but its convergence properties remain poorly
justified and there is no successful model that works both for correlation
function and for power spectrum. Here we present Halo Zeldovich approach
combined with perturbation theory (HZPT), in which we use standard perturbation
theory at one loop order (SPT) at very low $k$, and connect it to a version of
the halo model, for which we adopt the Zeldovich approximation plus a Pade
expansion of a compensated one halo term. This low $k$ matching allows us to
determine the one halo term amplitude and redshift evolution, both of which are
in an excellent agreement with simulations, and approximately agree with the
expected value from the halo model. Our Pade expansion approach of the one halo
term added to Zeldovich approximation identifies two typical halo scales
averaged over the halo mass function, the halo radius scale of order of 1Mpc/h,
and the halo mass compensation scale of order 26Mpc/h. The model gives better
than one percent accurate predictions for the correlation function above 5Mpc/h
at all redshifts, without any free parameters. With three fitted Pade expansion
coefficients the agreement in power spectrum is good to a percent up to $k \sim
1$h/Mpc, which can be improved to arbitrary $k$ by adding higher order terms in
Pade expansion. | Are redshift-space distortions actually a probe of growth of structure?: We present an impact of coupling between dark matter and a scalar field,
which might be responsible for dark energy, on measurements of redshift-space
distortions. We point out that, in the presence of conformal and/or disformal
coupling, linearized continuity and Euler equations for total matter fluid
significantly deviate from the standard ones even in the sub-horizon scales. In
such a case, a peculiar velocity of total matter field is determined not only
by a logarithmic time derivative of its density perturbation but also by
density perturbations for both dark matter and baryon, leading to a large
modification of the physical interpretation of observed data obtained by
measurements of redshift-space distortions. We reformulate galaxy two-point
correlation function in the redshift space based on the modified continuity and
Euler equations. We conclude from the resultant formula that the true value of
the linear growth rate of large-scale structure cannot be necessarily
constrained by single-redshift measurements of the redshift-space distortions,
unless one observes the actual time-evolution of structure. |
Formation of Planets by Hydrogravitational Dynamics: From hydro-gravitational cosmology, hydrogen-helium gas planets fragmented at
the plasma to gas transition 300,000 years after the big bang in
million-star-mass clumps. Stars may form in the clumps by mergers of the
planets to make globular star clusters. Star-less clumps persist as the dark
matter of galaxies as observed by Schild in 1996 using quasar microlensing, and
as predicted by Gibson in 1996 using fluid mechanics. Massive plasma
structures, at 10^46 kg proto-galaxy-cluster-mass, fragment at 30,000 years
when photon-viscous forces match gravitational fragmentation forces at the
horizon scale ct of the expanding universe, where c is the speed of light and t
is the time. Spinning proto-super-cluster-void and proto-galaxy-void boundaries
expand at sound speeds c/3^1/2 producing weak turbulence and linear-clusters of
gas-proto-galaxies that are fossils of turbulent-plasma vortex lines.
Hubble-space-telescope images of the most distant galaxies support this Gamov
1951 prediction. Vortex spin axes inferred from microwave background
anisotropies are interpreted as evidence of a turbulent big bang. A cosmic
distribution of life is attributed to hot water oceans of the interacting
hydrogen planets seeded by the first chemicals. | LOFAR: Recent imaging results & future prospects: The Low Frequency Array (LOFAR) is under construction in the Netherlands and
in several surrounding European countries. In this contribution, we describe
the layout and design of the telescope, with a particular emphasis on the
imaging characteristics of the array when used in its "standard imaging" mode.
After briefly reviewing the calibration and imaging software used for LOFAR
image processing, we show some recent results from the ongoing imaging
commissioning efforts. We conclude by summarizing future prospects for the use
of LOFAR in observing the little-explored low frequency Universe. |
The Obscured Fraction of AGN in the XMM-COSMOS Survey: A Spectral Energy
Distribution Perspective: The fraction of AGN luminosity obscured by dust and re-emitted in the mid-IR
is critical for understanding AGN evolution, unification, and parsec-scale AGN
physics. For unobscured (Type-1) AGN, where we have a direct view of the
accretion disk, the dust covering factor can be measured by computing the ratio
of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We
use this technique to estimate the obscured AGN fraction as a function of
luminosity and redshift for 513 Type-1 AGN from the XMM-COSMOS survey. The
re-processed and intrinsic luminosities are computed by fitting the 18-band
COSMOS photometry with a custom SED-fitting code, which jointly models emission
from: hot-dust in the AGN torus, the accretion disk, and the host-galaxy. We
find a relatively shallow decrease of the luminosity ratio as a function of
Lbol, which we interpret as a corresponding decrease in the obscured fraction.
In the context of the receding torus model, where dust sublimation reduces the
covering factor of more luminous AGN, our measurements require a torus height
which increases with luminosity as h ~ Lbol^{0.3-0.4}. Our obscured
fraction-luminosity relation agrees with determinations from SDSS censuses of
Type-1 and Type-2 quasars, and favors a torus optically thin to mid-IR
radiation. We find a much weaker dependence of obscured fraction on 2-10 keV
luminosity than previous determinations from X-ray surveys, and argue that
X-ray surveys miss a significant population of highly obscured Compton-thick
AGN. Our analysis shows no clear evidence for evolution of obscured fraction
with redshift. | Dark Matter Phase Transition Constrained at O(0.1) eV with LSB Rotation
Curves: In order to unravel the nature of the dark matter (DM) we have proposed a
particle-physics motivated model called Bound Dark Matter (BDM) that consist in
DM massless particles above a threshold energy Ec that acquire mass below it
due to nonperturbative methods. Therefore, the BDM model describes DM particles
which are relativistic, hot dark matter (HDM) in the denser (inner) regions of
galaxies and describes nonrelativistic, cold dark matter (CDM) where halo
density is below rho_c = Ec^4. We test this model by fitting rotation curves
from Low Surface Brightness (LSB) galaxies from The HI Nearby Galaxy Survey
(THINGS). We use a particular DM cored profile that contains three parameters:
a typical scale length (rs) and density (rho_0) of the halo, and a core radius
(rc) stemming from the relativistic nature of the BDM model. Since the energy
Ec parameterizes the phase transition due to the underlying particle physics
model, it is independent on the details of galaxy and/or structure formation
and therefore the DM profile parameters rs, rc, Ec are constrained, leaving
only two free parameters. Through the results we agree with previous ones
implying that cored profiles are preferred over the N-body motivated cuspy
profiles. We also compute 2D likelihoods of the BDM parameters rc and Ec for
the different galaxies and matter contents, and find an average galaxy core
radius rc = 1.48kpc and a transition energy between hot and cold dark matter at
Ec = 0.06 eV. The phase transition scale Ec is a new fundamental scale for our
DM model well motivated theoretical origin from gauge group dynamics. |
Mastering the effects of peculiar velocities in cosmic voids: How do peculiar velocities affect observed voids? To answer this question we
use the VIDE toolkit to identify voids in mock galaxy populations embedded
within an N-body simulation both with and without peculiar velocities included.
We compare the resulting void populations to assess the impact on void
properties. We find that void abundances and spherically-averaged radial
density profiles are mildly affected by peculiar velocities. However, peculiar
velocities can distort by up to 10% the shapes for a particular subset of voids
depending on the void size and density contrast, which can lead to increased
variance in Alcock-Paczy\'nski test. We offer guidelines for performing optimal
cuts on the void catalogue to reduce this variance by removing the most
severely affected voids while preserving the unaffected ones. In addition,
since this shape distortion is largely limited to the line of sight, we show
that the void radii are only affected at the $\sim$ 10% level and the
macrocenter positions at the $\sim$ 20% (even before performing cuts), meaning
that cosmological probes based on the Integrated Sachs-Wolfe and gravitational
lensing are not severely impacted by peculiar velocities. | Does $Λ$CDM really be in tension with the Hubble diagram data?: In this article, we elaborate further on the $\Lambda$CDM "tension",
suggested recently by the authors \cite{Lusso:2019akb,Risaliti:2018reu}. We
combine Supernovae type Ia (SNIa) with quasars (QSO) and Gamma Ray Bursts (GRB)
data in order to reconstruct a model independent Hubble diagram to as high
redshifts as possible. Specifically, in the case of either SNIa or SNIa/QSO
data, we find that current values of the cosmokinetic parameters extracted from
the Gaussian process are consistent with those of $\Lambda$CDM. Including GRBs,
in the analysis, we find a tension, which however is not as significant as that
mentioned in \cite{Lusso:2019akb, Risaliti:2018reu}. Finally, we argue that the
choice of the kernel function used in extracting the luminosity distance might
affect the amount of tension. |
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical
model. II. The colour-density relation up to z=1.5: [Abridged] We perform on galaxy mock catalogues the same colour-density
analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep
survey, and compare the results from mocks with observed data. We use mocks
with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-
analytic model by De Lucia & Blaizot (2007) applied to the Millennium
Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS
observational strategy (OMOCKS). We computed the B-band Luminosity Function LF
and the colour-density relation (CDR) in the mocks. We find that the LF in
mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of
the model LF is steeper than the VVDS one. Computing the LF for early and late
type galaxies, we show that mocks have an excess of faint early-type and of
bright late-type galaxies with respect to data. We find that the CDR in OMOCKS
is in excellent agreement with the one in CMOCKS. At z~0.7, the CDR in mocks
agrees with the VVDS one (red galaxies reside mainly in high densities). Yet,
the strength of the CDR in mocks does not vary within 0.2<z<1.5, while the
observed relation flattens with increasing z and possibly inverts at z=1.3. We
argue that the lack of evolution in the CDR in mocks is not due only to
inaccurate prescriptions for satellite galaxies, but that also the treatment of
central galaxies has to be revised. The reversal of the CDR can be explained by
wet mergers between young galaxies, producing a starburst event. This should be
seen on group scales. A residual of this is found in observations at z=1.5 on
larger scales, but not in the mocks, suggesting that the treatment of physical
processes affecting satellites and central galaxies in models should be
revised. | Molecular Tracers of Filamentary CO Emission Regions Surrounding the
Central Galaxies of Clusters: Optical emission is detected from filaments around the central galaxies of
clusters of galaxies. These filaments have lengths of tens of kiloparsecs. The
emission is possibly due to heating caused by the dissipation of mechanical
energy and by cosmic ray induced ionisation. CO millimeter and submillimeter
line emissions as well as H$_{2}$ infrared emission originating in such
filaments surrounding NGC~1275, the central galaxy of the Perseus cluster, have
been detected. Our aim is to identify those molecular species, other than CO,
that may emit detectable millimeter and submillimeter line features arising in
these filaments, and to determine which of those species will produce emissions
that might serve as diagnostics of the dissipation and cosmic ray induced
ionisation. The time-dependent UCL photon-dominated region modelling code was
used in the construction of steady-state models of molecular filamentary
emission regions at appropriate pressures, for a range of dissipation and
cosmic ray induced ionisation rates and incident radiation fields.HCO$^+$ and
C$_2$H emissions will potentially provide information about the cosmic ray
induced ionisation rates in the filaments. HCN and, in particular, CN are
species with millimeter and submillimeter lines that remain abundant in the
warmest regions containing molecules. Detections of the galaxy cluster
filaments in HCO$^{+}$, C$_{2}$H, and CN emissions and further detections of
them in HCN emissions would provide significant constraints on the dissipation
and cosmic ray induced ionisation rates. |
A New Probe of the Distribution of Dark Matter in Galaxies: The scale radius of dark matter halos is a critical parameter for specifying
the density distribution of dark matter, and is therefore a fundamental
parameter for modeling galaxies. We develop here a novel, observationally
motivated probe to quantitatively infer its value. We demonstrate that
disturbances in the extended atomic hydrogen gas disks of galaxies can be used
to infer the scale radius of dark matter halos. Our primary metric is the phase
of the $m=1$ mode of the disturbance in the outskirts of the gas disk, which we
take to be produced by a tidal interaction. We apply the method to the
Whirlpool Galaxy, which has an optically visible satellite. We explore
potential degeneracies due to orbital inclination and initial conditions and
find our results to be relatively insensitive to these considerations. Our
method of tracing the dark potential well through observed disturbances in
outer gas disks is complementary to gravitational lensing. | A Semi-analytic Ray-tracing Algorithm for Weak Lensing: We propose a new ray-tracing algorithm to measure the weak lensing shear and
convergence fields directly from N-body simulations. We calculate the
deflection of the light rays lensed by the 3-D mass density field or
gravitational potential along the line of sight on a grid-by-grid basis, rather
than using the projected 2-D lens planes. Our algorithm uses simple analytic
formulae instead of numerical integrations in the computation of the projected
density field along the line of sight, and so is computationally efficient,
accurate and straightforward to implement. This will prove valuable in the
interpretation of data from the next generation of surveys that will image many
thousands of square degrees of sky. |
Radiative feedback and the low efficiency of galaxy formation in
low-mass haloes at high redshift: Any successful model of galaxy formation needs to explain the low rate of
star formation in the small progenitors of today's galaxies. This inefficiency
is necessary for reproducing the low stellar-to-virial mass fractions,
suggested by current abundance matching models. A possible driver of this low
efficiency is the radiation pressure exerted by ionizing photons from massive
stars. The effect of radiation pressure in cosmological, zoom-in galaxy
formation simulations is modeled as a non-thermal pressure that acts only in
dense and optically thick star-forming regions. We also include photoionization
and photoheating by massive stars. The full photoionization of hydrogen reduces
the radiative cooling in the $10^{4-4.5}$ K regime. The main effect of
radiation pressure is to regulate and limit the high values of gas density and
the amount of gas available for star formation. This maintains a low star
formation rate of $\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}$ in halos with masses
about $10^{11} \ {M_\odot}$ at $z\simeq3$. Infrared trapping and
photoionization/photoheating processes are secondary effects in this mass
range. The galaxies residing in these low-mass halos contain only $\sim0.6\%$
of the total virial mass in stars, roughly consistent with abundance matching.
Radiative feedback maintains an extended galaxy with a rising circular velocity
profile. | The clustering of galaxies in the completed SDSS-III Baryon Oscillation
Spectroscopic Survey: Baryon Acoustic Oscillations in Fourier-space: We analyse the Baryon Acoustic Oscillation (BAO) signal of the final Baryon
Oscillation Spectroscopic Survey (BOSS) data release (DR12). Our analysis is
performed in Fourier-space, using the power spectrum monopole and quadrupole.
The dataset includes $1\,198\,006$ galaxies over the redshift range $0.2 < z <
0.75$. We divide this dataset into three (overlapping) redshift bins with the
effective redshifts $\zeff = 0.38$, $0.51$ and $0.61$. We demonstrate the
reliability of our analysis pipeline using N-body simulations as well as $\sim
1000$ MultiDark-Patchy mock catalogues, which mimic the BOSS-DR12 target
selection. We apply density field reconstruction to enhance the BAO
signal-to-noise ratio. By including the power spectrum quadrupole we can
separate the line-of-sight and angular modes, which allows us to constrain the
angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$ separately.
We obtain two independent $1.6\%$ and $1.5\%$ constraints on $D_A(z)$ and
$2.9\%$ and $2.3\%$ constraints on $H(z)$ for the low ($\zeff=0.38$) and high
($\zeff=0.61$) redshift bin, respectively. We obtain two independent $1\%$ and
$0.9\%$ constraints on the angular averaged distance $D_V(z)$, when ignoring
the Alcock-Paczynski effect. The detection significance of the BAO signal is of
the order of $8\sigma$ (post-reconstruction) for each of the three redshift
bins. Our results are in good agreement with the Planck prediction within
$\Lambda$CDM. This paper is part of a set that analyses the final galaxy
clustering dataset from BOSS. The measurements and likelihoods presented here
are combined with others in~\citet{Alam2016} to produce the final cosmological
constraints from BOSS. |
The clustering of intermediate redshift quasars as measured by the
Baryon Oscillation Spectroscopic Survey: We measure the quasar two-point correlation function over the redshift range
2.2<z<2.8 using data from the Baryon Oscillation Spectroscopic Survey. We use a
homogeneous subset of the data consisting of 27,129 quasars with spectroscopic
redshifts---by far the largest such sample used for clustering measurements at
these redshifts to date. The sample covers 3,600 square degrees, corresponding
to a comoving volume of 9.7(Gpc/h)^3 assuming a fiducial LambdaCDM cosmology,
and it has a median absolute i-band magnitude of -26, k-corrected to z=2. After
accounting for redshift errors we find that the redshift space correlation
function is fit well by a power-law of slope -2 and amplitude s_0=(9.7\pm
0.5)Mpc/h over the range 3<s<25Mpc/h. The projected correlation function, which
integrates out the effects of peculiar velocities and redshift errors, is fit
well by a power-law of slope -1 and r_0=(8.4\pm 0.6)Mpc/h over the range
4<R<16Mpc/h. There is no evidence for strong luminosity or redshift dependence
to the clustering amplitude, in part because of the limited dynamic range in
our sample. Our results are consistent with, but more precise than, previous
measurements at similar redshifts. Our measurement of the quasar clustering
amplitude implies a bias factor of b~3.5 for our quasar sample. We compare the
data to models to constrain the manner in which quasars occupy dark matter
halos at z~2.4 and infer that such quasars inhabit halos with a characteristic
mass of <M>~10^{12}Msun/h with a duty cycle for the quasar activity of 1 per
cent. | Highly asymmetric probability distribution from a finite-width upward
step during inflation: We study a single-field inflation model in which the inflaton potential has
an upward step between two slow-roll regimes by taking into account the finite
width of the step. We calculate the probability distribution function (PDF) of
the curvature perturbation $P[{\cal{R}}]$ using the $\delta N$ formalism. The
PDF has an exponential-tail only for positive ${\cal{R}}$ whose slope depends
on the step width. We find that the tail may have a significant impact on the
estimation of the primordial black hole abundance. We also show that the PDF
$P[{\cal{R}}]$ becomes highly asymmetric on a particular scale exiting the
horizon before the step, at which the curvature power spectrum has a dip. This
asymmetric PDF may leave an interesting signature in the large scale structure
such as voids. |
Supercluster A2142 and collapse in action - infalling and merging groups
and galaxy transformations: We study the dynamical state and properties of galaxies and groups in the
supercluster SClA2142 that has a collapsing core, to understand its possible
formation and evolution. We find the substructure of galaxy groups using normal
mixture modelling. We have used the projected phase space (PPS) diagram,
spherical collapse model, clustercentric distances, and magnitude gap between
the brightest galaxies in groups to study the dynamical state of groups and to
analyse group and galaxy properties. We compared the alignments of groups and
their brightest galaxies with the supercluster axis. The supercluster core has
a radius of about $8 h^{-1}$Mpc and total mass $M_{\mathrm{tot}} \approx
2.3\times~10^{15}h^{-1}M_\odot$ and is collapsing. Galaxies in groups on the
supercluster axis have older stellar populations than off-axis groups, with
median stellar ages $4 - 6$ and $< 4$Gyr, correspondingly. The cluster A2142
and the group Gr8 both host galaxies with the oldest stellar populations among
groups in SClA2142 having the median stellar age $t > 8$Gyr. Recently quenched
galaxies and active galactic nuclei (AGNs) are mostly located at virial radii
or in merging regions of groups, and at clustercentric distances $D_c \approx 6
h^{-1}$ Mpc. The most elongated groups lie along the supercluster axis and are
aligned with it. Magnitude gaps between the brightest galaxies of groups are
less than one magnitude, suggesting that groups in SClA2142 are dynamically
young. The collapsing core of the supercluster, infall of galaxies and groups,
and possible merging groups, which affect galaxy properties and may trigger the
activity of AGNs, show how the whole supercluster is evolving. | Degree-Scale CMB Polarization Measurements from Three Years of BICEP1
Data: BICEP1 is a millimeter-wavelength telescope designed specifically to measure
the inflationary B-mode polarization of the Cosmic Microwave Background (CMB)
at degree angular scales. We present results from an analysis of the data
acquired during three seasons of observations at the South Pole (2006 to 2008).
This work extends the two-year result published in Chiang et al. (2010), with
additional data from the third season and relaxed detector-selection criteria.
This analysis also introduces a more comprehensive estimation of band-power
window functions, improved likelihood estimation methods and a new technique
for deprojecting monopole temperature-to-polarization leakage which reduces
this class of systematic uncertainty to a negligible level. We present maps of
temperature, E- and B-mode polarization, and their associated angular power
spectra. The improvement in the map noise level and polarization spectra error
bars are consistent with the 52% increase in integration time relative to
Chiang et al. (2010). We confirm both self-consistency of the polarization data
and consistency with the two-year results. We measure the angular power spectra
at 21 <= l <= 335 and find that the EE spectrum is consistent with Lambda Cold
Dark Matter (LCDM) cosmology, with the first acoustic peak of the EE spectrum
now detected at 15sigma. The BB spectrum remains consistent with zero. From
B-modes only, we constrain the tensor-to-scalar ratio to r = 0.03+0.27-0.23, or
r < 0.70 at 95% confidence level. |
Enhanced Small-Scale Structure in the Cosmic Dark Ages: We consider the consequences of a matter power spectrum which rises on small
scales until eventually being cutoff by microphysical processes associated with
the particle nature of dark matter. Evolving the perturbations of a weakly
interacting massive particle from before decoupling until deep in the nonlinear
regime, we show that nonlinear structure can form abundantly at very high
redshifts. In such a scenario, dark matter annihilation is substantially
increased after matter-radiation equality. Furthermore, since the power
spectrum can be increased over a broad range of scales, the first star forming
halos may form earlier than usual as well. The next challenge is determining
how early Universe observations may constrain such enhanced dark matter
perturbations. | A natural origin of primordial density perturbations: We suggest here a mechanism for the seeding of the primordial density
fluctuations. We point out that a process like reheating at the end of
inflation will inevitably generate perturbations, even on superhorizon scales,
by the local diffusion of energy. Provided that the reheating temperature is of
order the GUT scale, the density contrast $\delta_R$ for spheres of radius $R$
will be of order $10^{-5}$ at horizon entry, consistent with the values
measured by \texttt{WMAP}. If this were a purely classical process,
$\delta_R^2$ would fall as $1/R^4$ beyond the horizon, and the resulting
primordial density power spectrum would be $P(k) \propto k^n$ with $n=4$.
However, as shown by Gabrielli et al, a quantum diffusion process can generate
a power spectrum with any index in the range $0<n\leq 4$, including values
close to the observed $n=1$ ($\delta_R^2$ will then be $\propto 1/R^{3+n}$ for
$n<1$ and $1/R^4$ for $n>1$). Thus, the two characteristic parameters that
determine the appearance of present day structures could be natural
consequences of this mechanism. These are in any case the minimum density
variations that must have formed if the universe was rapidly heated to GUT
temperatures by the decay of a `false vacuum'. There is then no \emph{a priori}
necessity to postulate additional (and fine tuned) quantum fluctuations in the
`false vacuum', nor a pre-inflationary period. Given also the very stringent
pre-conditions required to trigger a satisfactory period of inflation,
altogether it seems at least as natural to assume that the universe began in a
flat and homogeneously expanding phase. |
Finding Early Supernovae at 5 $< z <$ 12 with Frontier Fields: Supernovae are important probes of the properties of stars at high redshifts
because they can be detected at early epochs and their masses can be inferred
from their light curves. Direct detection of the first cosmic explosions in the
universe will only be possible with JWST, WFIRST and the next generation of
extremely large telescopes. But strong gravitational lensing by massive
clusters, like those in the Frontier Fields, could reveal supernovae at
slightly lower redshifts now by magnifying their flux by factors of 10 or more.
We find that Frontier Fields will likely discover dozens of core-collapse
supernovae at 5 $ < z <$ 12. Future surveys of cluster lenses similar in scope
to Frontier Fields by JWST might find hundreds of these events out to $z \sim$
15 - 17. Besides revealing the masses of early stars, these ancient supernovae
could also constrain cosmic star formation rates in the era of first galaxy
formation. | Primordial black holes induced stochastic axion-photon oscillations in
primordial magnetic field: Primordial black holes (PBHs) can be produced in the very early Universe due
to the large density fluctuations. The cosmic background of axion-like
particles (ALPs) could be non-thermally generated by PBHs. In this paper, we
investigate the ALPs emitted by ultra-light PBHs with the mass range $10 \,
{\rm g} \lesssim M_{\rm PBH} \lesssim 10^9 \, \rm g$, in which PBHs would have
completely evaporated before the start of Big Bang Nucleosynthesis (BBN) and
can therefore not be directly constrained. In this case, the minimal scenario
that ALPs could interact only with photons is supposed. We study the stochastic
oscillations between the ALPs and photons in the cosmic magnetic field in
detail. The primordial magnetic field (PMF) can be modelled as the stochastic
background field model with the completely non-homogeneous component of the
cosmic plasma. Using the latest stringent limits on PMF, we show the numerical
results of ALP-photon oscillation probability distributions with the
homogeneous and stochastic magnetic field scenarios. The PBH-induced stochastic
ALP-photon oscillations in the PMF may have the effects on some further
phenomena, such as the cosmic microwave background (CMB), the cosmic X-ray
background (CXB), and the extragalactic gamma-ray background (EGB). |
f(R) as a dark energy fluid: We study the equations for the evolution of cosmological perturbations in
$f\left(\mathcal{R}\right)$ and conclude that this modified gravity model can
be expressed as a dark energy fluid at background and linearised perturbation
order. By eliminating the extra scalar degree of freedom known to be present in
such theories, we are able to characterise the evolution of the perturbations
in the scalar sector in terms of equations of state for the entropy
perturbation and anisotropic stress which are written in terms of the density
and velocity perturbations of the dark energy fluid and those in the matter, or
the metric perturbations. We also do the same in the much simpler vector and
tensor sectors. In order to illustrate the simplicity of this formulation, we
numerically evolve perturbations in a small number of cases. | Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies
at z>1: We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional emission-line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic diagnostics ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha) remain
consistent with X-ray AGN/SF classification. The X-ray data also suggest that
"composite" galaxies (with intermediate AGN/SF classification) host bona-fide
AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have nuclear activity
detected by either X-rays or the classic diagnostics. Compared to the X-ray and
line ratio classifications, the mass-excitation method remains effective at
z>1, but we show that the color-excitation method requires a new calibration to
successfully identify AGNs at these redshifts. |
The Southern 2MASS AGN Survey: spectroscopic follow-up with 6dF: The Two Micron All-Sky Survey (2MASS) has provided a uniform photometric
catalog to search for previously unknown red AGN and QSOs. We have extended the
search to the southern equatorial sky by obtaining spectra for 1182 AGN
candidates using the 6dF multifibre spectrograph on the UK Schmidt Telescope.
These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey.
The candidates were selected using a single color cut of J - Ks > 2 to Ks ~
15.5 and a galactic latitude of |b|>30 deg. 432 spectra were of sufficient
quality to enable a reliable classification. 116 sources (or ~27%) were
securely classified as type 1 AGN, 20 as probable type 1s, and 57 as probable
type 2 AGN. Most of them span the redshift range 0.05<z<0.5 and only 8 (or ~6%)
were previously identified as AGN or QSOs. Our selection leads to a
significantly higher AGN identification rate amongst local galaxies (>20%) than
in any previous galaxy survey. A small fraction of the type 1 AGN could have
their optical colors reddened by optically thin dust with A_V<2 mag relative to
optically selected QSOs. A handful show evidence for excess far-IR emission.
The equivalent width (EW) and color distributions of the type 1 and 2 AGN are
consistent with AGN unified models. In particular, the EW of the [OIII]
emission line weakly correlates with optical--near-IR color in each class of
AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the
optical properties of the 2MASS red AGN are not dramatically different from
those of optically-selected QSOs. Our near-IR selection appears to detect the
most near-IR luminous QSOs in the local universe to z~0.6 and provides
incentive to extend the search to deeper near-IR surveys. | Search for low-frequency diffuse radio emission around a shock in the
massive galaxy cluster MACS J0744.9+3927: Merging galaxy clusters produce low Mach number shocks in the intracluster
medium. These shocks can accelerate electrons to relativistic energies that are
detectable at radio frequencies. MACS J0744.9+3927 is a massive ($M_{500} =
(11.8 \pm 2.8) \times 10^{14} M_{\odot}$), high-redshift ($z=0.6976$) cluster
where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich
maps from MUSTANG indicate that a shock, with Mach number $\mathcal{M} =
1.0-2.9$ and an extension of $\sim 200$ kpc, sits near the centre of the
cluster. The shock is also detected as a brightness and temperature
discontinuity in X-ray observations. To search for diffuse radio emission
associated with the merger, we have imaged the cluster with the LOw Frequency
ARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previously
undetected AGN emission, but do not show clear cluster-scale diffuse emission
in the form of a radio relic nor a radio halo. The region of the shock is on
the western edge of AGN lobe emission from the brightest cluster galaxy.
Correlating the flux of known shock-induced radio relics versus their size, we
find that the radio emission overlapping the shocked region in MACS
J0744.9+3927 is likely of AGN origin. We argue against the presence of a relic
caused by diffusive shock acceleration and suggest that the shock is too weak
to accelerate electrons from the intracluster medium. |
The molecular gas in Luminous Infrared Galaxies I: CO lines, extreme
physical conditions, and their drivers: We report results from a large molecular line survey of Luminous Infrared
Galaxies (L_{IR} >= 10^{11} L_sol) in the local Universe (z<=0.1), conducted
during the last decade with the James Clerk Maxwell Telescope (JCMT) and the
IRAM 30-m telescope. This work presents the CO and {13}CO line data for 36
galaxies, further augmented by multi-J total CO luminosities available for
other IR-bright galaxies from the literature. This yields a sample of N=70
galaxies with the star-formation (SF) powered fraction of their IR luminosities
spanning L_{IR} (10^{10}-2x10^{12}) L_sol and a wide range of morphologies.
Simple comparisons of their available CO Spectral Line Energy Distributions
(SLEDs) with local ones, as well as radiative transfer models discern a
surprisingly wide range of average ISM conditions, with most of the surprises
found in the high-excitation regime. These take the form of global CO SLEDs
dominated by a very warm (T_{kin}>=100 K) and dense (n>=10^4 cm^{-3}) gas
phase, involving galaxy-sized (~(few)x10^9 M_sol) gas mass reservoirs under
conditions that would otherwise amount only ~1% of mass per typical SF
molecular cloud in the Galaxy. Some of the highest excitation CO SLEDs are
found in the so-called Ultra Luminous Infrared Galaxies and seem irreducible to
ensembles of ordinary SF-powered regions. Highly supersonic turbulence and high
cosmic ray (CR) energy densities rather than far-UV/optical photons or
SNR-induced shocks from individual SF sites can globally warm the large amounts
of dense gas found in these merger-driven starbursts and easily power their
extraordinary CO line excitation..... | Scale Dependence of the Halo Bias in General Local-Type Non-Gaussian
Models I: Analytical Predictions and Consistency Relations: We investigate the clustering of halos in cosmological models starting with
general local-type non-Gaussian primordial fluctuations. We employ multiple
Gaussian fields and add local-type non-Gaussian corrections at arbitrary order
to cover a class of models described by frequently-discussed f_nl, g_nl and
\tau_nl parameterization. We derive a general formula for the halo power
spectrum based on the peak-background split formalism. The resultant spectrum
is characterized by only two parameters responsible for the scale-dependent
bias at large scale arising from the primordial non-Gaussianities in addition
to the Gaussian bias factor. We introduce a new inequality for testing
non-Gaussianities originating from multi fields, which is directly accessible
from the observed power spectrum. We show that this inequality is a
generalization of the Suyama-Yamaguchi inequality between f_nl and \tau_nl to
the primordial non-Gaussianities at arbitrary order. We also show that the
amplitude of the scale-dependent bias is useful to distinguish the simplest
quadratic non-Gaussianities (i.e., f_nl-type) from higher-order ones (g_nl and
higher), if one measures it from multiple species of galaxies or clusters of
galaxies. We discuss the validity and limitations of our analytic results by
comparison with numerical simulations in an accompanying paper. |
Direct test of the FLRW metric from strongly lensed gravitational wave
observations: The assumptions of large-scale homogeneity and isotropy underly the familiar
Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) metric that appears to be an
accurate description of our Universe. In this paper, we propose a new strategy
of testing the validity of the FLRW metric, based on the galactic-scale lensing
systems where strongly lensed gravitational waves and their electromagnetic
counterparts can be simultaneously detected. Each strong lensing system creates
opportunity to infer the curvature parameter of the Universe. Consequently,
combined analysis of many such systems will provide a model-independent tool to
test the validity of the FLRW metric. Our study demonstrates that the
third-generation ground based GW detectors, like the Einstein Telescope (ET)
and space-based detectors, like the Big Bang Observer (BBO), are promising
concerning determination of the curvature parameter or possible detection of
deviation from the FLRW metric. Such accurate measurements of the FLRW metric
can become a milestone in precision GW cosmology. | Clustering in Massive Neutrino Cosmologies via Eulerian Perturbation
Theory: We introduce an Eulerian Perturbation Theory to study the clustering of
tracers for cosmologies in the presence of massive neutrinos. Our approach is
based on mapping recently-obtained Lagrangian Perturbation Theory results to
the Eulerian framework. We add Effective Field Theory counterterms,
IR-resummations and a biasing scheme to compute the one-loop redshift-space
power spectrum. To assess our predictions, we compare the power spectrum
multipoles against synthetic halo catalogues from the Quijote simulations,
finding excellent agreement on scales $k\lesssim 0.25 \,h \text{Mpc}^{-1}$. One
can obtain the same fitting accuracy using higher wave-numbers, but then the
theory fails to give a correct estimation of the linear bias parameter. We
further discuss the implications for the tree-level bispectrum. Finally,
calculating loop corrections is computationally costly, hence we derive an
accurate approximation wherein we retain only the main features of the kernels,
as produced by changes to the growth rate. As a result, we show how FFTLog
methods can be used to further accelerate the loop computations with these
reduced kernels. |
Footprints of Loop I on Cosmic Microwave Background Maps: Cosmology has made enormous progress through studies of the cosmic microwave
background, however the subtle signals being now sought such as B-mode
polarisation due to primordial gravitational waves are increasingly hard to
disentangle from residual Galactic foregrounds in the derived CMB maps. We
revisit our finding that on large angular scales there are traces of the nearby
old supernova remnant Loop I in the WMAP 9-year map of the CMB and confirm this
with the new SMICA map from the Planck satellite. | VLT Optical BVR observations of two bright Supernova Ia hosts in the
Virgo cluster: We study the two galaxies NGC4621 and NGC4374 in the Virgo cluster to derive
their distances and stellar population properties. The targets have hosted
three type Ia Supernova events allowing to investigate the correlations between
the SNeIa and their host stellar systems. Using deep BVR data, obtained with
FORS2 at the VLT, we analyse the Surface Brightness Fluctuations (SBF)
properties of the targets. We adopt our measurements and existing calibrations
to estimate the distance of NGC4621 and NGC4374. For stellar population
analysis, we measured SBF amplitudes in different galaxy regions. We present a
detailed comparison between data and models to constrain the characteristics of
the dominant stellar components at i) various galactic radii, and ii) in the
regions where SNeIa were recorded. Our V and R SBF measures provide distances
in agreement with literature estimates. The median of our and literature
SBF-based distances agrees with the one from non-SBF methods. Comparing data
with models we find that stellar populations properties do not change
significantly along galactic radius, with a dominant population having old age
and solar chemical composition. The galaxies appear similar in all properties
analysed, except for B-band SBF. Since the SBF magnitudes in this band are
sensitive to the properties of a hot stellar component, we speculate that such
behaviour is a consequence of different diffuse hot components in the galaxies.
We find that the presence of a percentage of hot-HB stars in old and metal rich
stellar populations could be at the origin of the observed differences. We find
a good uniformity in the V and R SBF and integrated colours in the regions
where the three SNeIa exploded. On the other hand, the B-band SBF signal shows
intriguing differences. |
Cosmology with gamma-ray bursts: I. The Hubble diagram through the
calibrated $E_{\rm p,i}$ - $E_{\rm iso}$ correlation: Gamma-ray bursts are the most energetic explosions in the Universe. They are
detectable up to very high redshifts, therefore can be used to study the
expansion rate of the Universe and to investigate the observational properties
of dark energy, provided that empirical correlations between spectral and
intensity properties are appropriately calibrated. We used the type Ia
supernova luminosity distances to calibrate the correlation between the peak
photon energy, $E_{p, i}$, and the isotropic equivalent radiated energy, $
E_{iso}$ in GRBs. With this correlation, we tested the reliability of applying
GRBs to measure cosmological parameters and to obtain indications on the basic
properties and evolution of dark energy. Using 162 GRBs with measured redshifts
and spectra, we applied a local regression technique to calibrate the $E_{p,
i}$-$E_{iso}$ correlation against the type Ia SN data to build a calibrated GRB
Hubble diagram. We tested the possible redshift dependence of the correlation
and its effect on the Hubble diagram. Finally, we used the GRB Hubble diagram
to investigate the dark energy EOS. For this, we focused on the so-called
Chevalier-Polarski-Linder (CPL) parametrization of the dark energy EOS and
implemented the Markov chain Monte Carlo (MCMC) method to efficiently sample
the space of cosmological parameters. Our analysis shows once more that the
$E_{p, i}$-$E_{iso}$ correlation has no significant redshift dependence.
Therefore the high-redshift GRBs can be used as a cosmological tool to
determine the basic cosmological parameters and to test different models of
dark energy in the redshift region ($z\geqslant 3$), which is unexplored by the
SNIa and baryonic acoustic oscillations data. Our updated calibrated Hubble
diagram of GRBs provides some marginal indication (at $1\sigma$ level) of an
evolving dark energy EOS. | Motion induced second order temperature and y-type anisotropies after
the subtraction of linear dipole in the CMB maps: y-type spectral distortions of the cosmic microwave background allow us to
detect clusters and groups of galaxies, filaments of hot gas and the
non-uniformities in the warm hot intergalactic medium. Several CMB experiments
(on small areas of sky) and theoretical groups (for full sky) have recently
published y-type distortion maps. We propose to search for two artificial hot
spots in such y-type maps resulting from the incomplete subtraction of the
effect of the motion induced dipole on the cosmic microwave background sky.
This dipole introduces, at second order, additional temperature and
y-distortion anisotropy on the sky of amplitude few \mu K which could
potentially be measured by Planck HFI and Pixie experiments and can be used as
a source of cross channel calibration by CMB experiments. This y-type
distortion is present in every pixel and is not the result of averaging the
whole sky. This distortion, calculated exactly from the known linear dipole,
can be subtracted from the final y-type maps, if desired. |
An improved Halo Occupation Distribution prescription from UNITsim
H_alpha Emission Line Galaxies: conformity and modified radial profile: Emission line galaxies (ELGs) are targeted by the new generation of
spectroscopic surveys to make unprecedented measurements in cosmology from
their distribution. Accurately interpreting this data requires understanding
the imprints imposed by the physics of galaxy formation and evolution on galaxy
clustering. In this work we utilize a semi-analytical model of galaxy formation
(SAGE) to explore the necessary components for accurately reproducing the
clustering of ELGs. We focus on developing a Halo Occupation Distribution (HOD)
prescription able to reproduce the clustering of SAGE galaxies. Typically, HOD
models assume that satellite and central galaxies of a given type are
independent events. We investigate the need for conformity, i.e. whether the
average satellite occupation depends on the existence of a central galaxy of a
given type. Incorporating conformity into HOD models is crucial for reproducing
the clustering in the reference galaxy sample. Another aspect we investigate is
the radial distribution of satellite galaxies within haloes. The traditional
density profile models, NFW and Einasto profiles, fail to accurately replicate
the small-scale clustering measured for SAGE satellite galaxies. To overcome
this limitation, we propose a generalization of the NFW profile, thereby
enhancing our understanding of galaxy clustering. | Semi-holographic model revisited: In a recent work Zhang, Li and Noh [Phys. Lett. B {\bf 694}, 177
(2010)]proposed a model for dark energy assuming this component strictly obeys
the holographic principle. They performed a dynamical system analysis, finding
a scaling solution which is helpful to solve the coincidence problem. However
they need explicitly a cosmological constant. In this paper we derive an
explicit analytical solution, without $\Lambda$, that shows agreement with the
Supernovae data. However this solution is not physical because violate all the
energy conditions. |
Quintessence versus phantom dark energy: the arbitrating power of
current and future observations: We analyze the possibility to distinguish between quintessence and phantom
scalar field models of dark energy using observations of luminosity distance
moduli of SNe Ia, CMB anisotropies and polarization, matter density
perturbations and baryon acoustic oscillations. Among the present observations
only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic
oscillations may be able to decide between quintessence or phantom scalar field
models, however for each model a set of best-fit parameters exists, which
matches all data with similar goodness of fit. We compare the relative
differences of best-fit model predictions with observational uncertainties for
each type of data and we show that the accuracy of SNe Ia luminosity distance
data is far from the one necessary to distinguish these types of dark energy
models, while the CMB data (WMAP, ACT, SPT and especially Planck) are close to
being able to reliably distinguish them. Also an improvement of the large-scale
structure data (future releses of SDSS BOSS and e.g. Euclid or BigBOSS) will
enable us to surely decide between quintessence and phantom dark energy. | Step potentials for Dark Energy: We consider a reconstructing scheme using observational data from SNIa, BAO
and CMB, based on a model of dark unification using a single non-minimally
coupled scalar field. We investigate through a reconstruction program, the main
features the current observational data imposes to the scalar field potential.
We found that the form suggested by observations implies a step feature in the
potential, where the kinetic and potential energy becomes of the same order of
magnitude. |
Discrepancies between CFHTLenS cosmic shear & Planck: new physics or
systematic effects?: There is currently a discrepancy in the measured value of the amplitude of
matter clustering, parameterised using $\sigma_8$, inferred from galaxy weak
lensing, and cosmic microwave background data, which could be an indication of
new physics, such as massive neutrinos or a modification to the gravity law, or
baryon feedback. In this paper we make the assumption that the cosmological
parameters are well determined by Planck, and use weak lensing data to
investigate the implications for baryon feedback and massive neutrinos, as well
as possible contributions from intrinsic alignments and biases in photometric
redshifts. We apply a non-parametric approach to model the baryonic feedback on
the dark matter clustering, which is flexible enough to reproduce the OWLS and
Illustris simulation results. The statistic we use, 3D cosmic shear, is a
method that extracts cosmological information from weak lensing data using a
spherical-Bessel function power spectrum approach. We analyse the CFHTLenS weak
lensing data and, assuming best fit cosmological parameters from the Planck CMB
experiment, find that there is no evidence for baryonic feedback on the dark
matter power spectrum, but there is evidence for a bias in the photometric
redshifts in the CFHTLenS data, consistent with a completely independent
analysis by Choi et al. (2015), based on spectroscopic redshifts; and that
these conclusions are robust to assumptions about the intrinsic alignment
systematic. We also find an upper limit on the sum of neutrino masses
conditional on other $\Lambda$CDM parameters being fixed, of $< 0.28$ eV
($1\sigma$). | Generation of Arbitrarily Non-Gaussian Fields with a Set Correlation
Structure: Non-Gaussianity in the cosmic microwave background and the large-scale
structure of galaxies provides an increasingly powerful probe of the universe.
I implement an algorithm to generate realisations of fields that possess an
arbitrary probability distribution function and an arbitrary power spectrum and
demonstrate the code with a number of examples, including the uniform
distribution, the Laplace distribution, the $\chi$ and $\chi^2$ distributions,
Rayleigh and Maxwell-Boltzmann distributions. The code is available at
http://sourceforge.net/projects/nongaussian. |
A wide Chandra view of the core of the Perseus cluster: We present new Chandra images of the X-ray emission from the core of the
Perseus cluster of galaxies. The total observation time is now 1.4 Ms. New
depressions in X-ray surface brightness are discovered to the north of NGC1275,
which we interpret as old rising bubbles. They imply that bubbles are
long-lived and do not readily breakup when rising in the hot cluster
atmosphere. The existence of a 300 kpc long NNW-SSW bubble axis means there
cannot be significant transverse large scale flows exceeding 100 km/s.
Interesting spatial correlations are seen along that axis in early deep radio
maps. A semi-circular cold front about 100 kpc west of the nucleus is seen. It
separates an inner disturbed region dominated by the activity of the active
nucleus of NGC1275 from the outer region where a subcluster merger dominates. | Equivalence Principle and the Baryon Acoustic Peak: We study the dominant effect of a long wavelength density perturbation
$\delta(\lambda_L)$ on short distance physics. In the non-relativistic limit,
the result is a uniform acceleration, fixed by the equivalence principle, and
typically has no effect on statistical averages due to translational
invariance. This same reasoning has been formalized to obtain a "consistency
condition" on the cosmological correlation functions. In the presence of a
feature, such as the acoustic peak at $l_{\rm BAO}$, this naive expectation
breaks down for $\lambda_L<l_{\rm BAO}$. We calculate a universal piece of the
three-point correlation function in this regime. The same effect is shown to
underlie the spread of the acoustic peak, and is calculable to all orders in
the long modes. This can be used to improve the result of perturbative
calculations - a technique known as "infra-red resummation" - and is explicitly
applied to the one-loop calculation of power spectrum. Finally, the success of
BAO reconstruction schemes is argued to be another empirical evidence for the
validity of the results. |
Cross-Correlation of Planck CMB Lensing with DESI-Like LRGs: Cross-correlations between the lensing of the cosmic microwave background
(CMB) and other tracers of large-scale structure provide a unique way to
reconstruct the growth of dark matter, break degeneracies between cosmology and
galaxy physics, and test theories of modified gravity. We detect a
cross-correlation between DESI-like luminous red galaxies (LRGs) selected from
DECaLS imaging and CMB lensing maps reconstructed with the Planck satellite at
a significance of $S/N = 27.2$ over scales $\ell_{\rm min} = 30$, $\ell_{\rm
max} = 1000$. To correct for magnification bias, we determine the slope of the
LRG cumulative magnitude function at the faint limit as $s = 0.999 \pm 0.015$,
and find corresponding corrections on the order of a few percent for $C^{\kappa
g}_{\ell}, C^{gg}_{\ell}$ across the scales of interest. We fit the large-scale
galaxy bias at the effective redshift of the cross-correlation $z_{\rm eff}
\approx 0.68$ using two different bias evolution agnostic models: a HaloFit
times linear bias model where the bias evolution is folded into the
clustering-based estimation of the redshift kernel, and a Lagrangian
perturbation theory model of the clustering evaluated at $z_{\rm eff}$. We also
determine the error on the bias from uncertainty in the redshift distribution;
within this error, the two methods show excellent agreement with each other and
with DESI survey expectations. | Globular Cluster Systems of Early-type Galaxies in Low-density
Environments: Deep images of 10 early-type galaxies in low-density environments have been
obtained with the Advanced Camera for Surveys (ACS) on the Hubble Space
Telescope. The global properties of the globular cluster (GC) systems of the
galaxies have been derived in order to investigate the role of the environment
in galaxy formation and evolution. Using the ACS Virgo Cluster Survey (ACSVCS)
as a high-density counterpart, the similarities and differences between the GC
properties in high- and low-density environments are presented. We find a
strong correlation of the GC mean colours and the degree of colour bimodality
with the host galaxy luminosity in low-density environments, in good agreement
with high-density environments. In contrast, the GC mean colours at a given
host luminosity are somewhat bluer (\Delta(g-z) ~ 0.05) than those for cluster
galaxies, indicating more metal-poor (\Delta[Fe/H] ~ 0.10-0.15) and/or younger
(\Delta age > 2 Gyr) GC systems than those in dense environments. Furthermore,
with decreasing host luminosity, the colour bimodality disappears faster, when
compared to galaxies in cluster environments. Our results suggest that: (1) in
both high- and low-density environments, the mass of the host galaxy has the
dominant effect on GC system properties, (2) the local environment has only a
secondary effect on the history of GC system formation, (3) GC formation must
be governed by common physical processes across a range of environments. |
Galaxy bias from galaxy-galaxy lensing in the DES Science Verification
Data: We present a measurement of galaxy-galaxy lensing around a magnitude-limited
($i_{AB} < 22.5$) sample of galaxies from the Dark Energy Survey Science
Verification (DES-SV) data. We split these lenses into three
photometric-redshift bins from 0.2 to 0.8, and determine the product of the
galaxy bias $b$ and cross-correlation coefficient between the galaxy and dark
matter overdensity fields $r$ in each bin, using scales above 4 Mpc/$h$
comoving, where we find the linear bias model to be valid given our current
uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing
with those obtained from galaxy clustering (Crocce et al. 2016) and CMB lensing
(Giannantonio et al. 2016) for the same sample of galaxies, and find our
measurements to be in good agreement with those in Crocce et al. (2016), while,
in the lowest redshift bin ($z\sim0.3$), they show some tension with the
findings in Giannantonio et al. (2016). We measure $b\cdot r$ to be $0.87\pm
0.11$, $1.12 \pm 0.16$ and $1.24\pm 0.23$, respectively for the three redshift
bins of width $\Delta z = 0.2$ in the range $0.2<z <0.8$, defined with the
photometric-redshift algorithm BPZ. Using a different code to split the lens
sample, TPZ, leads to changes in the measured biases at the 10-20\% level, but
it does not alter the main conclusion of this work: when comparing with Crocce
et al. (2016) we do not find strong evidence for a cross-correlation parameter
significantly below one in this galaxy sample, except possibly at the lowest
redshift bin ($z\sim 0.3$), where we find $r = 0.71 \pm 0.11$ when using TPZ,
and $0.83 \pm 0.12$ with BPZ. | Gravitational waves from first order cosmological phase transitions in
the Sound Shell Model: We calculate gravitational wave power spectra from first order early Universe
phase transitions using the Sound Shell Model. The model predicts that the
power spectrum depends on the mean bubble separation, the phase transition
strength, the phase boundary speed, with the overall frequency scale set by the
nucleation temperature. There is also a dependence on the time evolution of the
bubble nucleation rate. The gravitational wave peak power and frequency are in
good agreement with published numerical simulations, where bubbles are
nucleated simultaneously. Agreement is particularly good for detonations, but
the total power for deflagrations is predicted higher than numerical
simulations show, indicating refinement of the model of the transfer of energy
to the fluid is needed for accurate computations. We show how the
time-dependence of the bubble nucleation rate affects the shape of the power
spectrum: an exponentially rising nucleation rate produces higher amplitude
gravitational waves at a longer wavelength than simultaneous nucleation. We
present an improved fit for the predicted gravitational wave power spectrum in
the form of a double broken power law, where the two breaks in the slope happen
at wavenumber corresponding to the mean bubble separation and the thickness of
the fluid shell surrounding the expanding bubbles, which in turn is related to
the difference of the phase boundary speed from the speed of sound. |
PPAK Wide field Integral Field Spectroscopy of NGC 628 III. Stellar
population properties: We present a stellar population analysis of the nearby, face-on, SA(s)c
galaxy, NGC628, which is part of the PPAK IFS Nearby Galaxies Survey (PINGS).
The data cover a field of view of ~6 arcmin in diameter with a sampling of
$\sim$2.7 arcsec per spectrum and a wavelength range (3700-7000A). We apply
spectral inversion methods to derive 2-dimensional maps of star formation
histories and chemical enrichment. We present maps of the mean (luminosity- and
mass-weighted) age and metallicity that reveal the presence of structures such
as a nuclear ring, previously seen in molecular gas. The disk is dominated in
mass by an old stellar component at all radii sampled by our data, while the
percentage of young stars increase with radius. The mean stellar age and
metallicity profiles have a two defined regions, an inner one with flatter
gradients (even slightly positive) and an external ones with a negative,
steeper one, separated at $\sim$60 arcsec. This break in the profiles is more
prominent in the old stellar component. The young component shows a metallicity
gradient that is very similar to that of the gas, and that is flatter in the
whole disc. The agreement between the metallicity gradient of the young stars
and the gas, and the recovery of the measured colours from our derived star
formation histories validate the techniques to recover the age-metallicity and
the star formation histories in disc galaxies from integrated spectra. We
speculate about the possible origin of the break and conclude that the most
likely scenario is that we are seeing, in the center of NGC 628, a dissolving
bar, as predicted in some numerical simulations. | Probing spectral properties of radio-quiet quasars searched for optical
microvariability: We obtained SDSS spectra for a set of 37 radio-quiet quasars (RQQSOs) that
had been previously examined for rapid small scale optical variations, or
microvariability. Their H-beta and Mg II emission lines were carefully fit to
determine line widths (FWHM) as well as equivalent widths (EW) due to the broad
emission line components. The line widths were used to estimate black hole
masses and Eddington ratios, ell. Both EW and FWHM are anticorrelated with ell.
The EW distributions provide no evidence for the hypothesis that a weak jet
component in the RQQSOs is responsible for their microvariability. |
Searching for cosmological signatures of the Einstein equivalence
principle breaking: Modifications of gravity generated by a multiplicative coupling of a scalar
field to the electromagnetic Lagrangian lead to a breaking of Einstein
equivalence principle (EEPB) as well as to variations of fundamental constants.
In these theoretical frameworks, deviations of standard values of the fine
structure constant, $\Delta \alpha/\alpha=\phi$, and of the cosmic distance
duality relation, $D_L(1+z)^{-2}/D_A=\eta=1$, where $D_L$ and $D_A$ are the
luminosity and angular diameter distances, respectively, are unequivocally
linked. In this paper, we search for cosmological signatures of the EEPB by
using angular diameter distance from galaxy clusters, obtained via their
Sunyaev-Zeldovich effect (SZE) and X-ray observations, and distance modulus of
type Ia supernovae (SNe Ia). The crucial point here is that we take into
account the dependence of the SZE/X-ray technique with $\phi$ and $\eta$. Our
new results show no indication of the EEPB. | Non-linear power spectra in the synchronous gauge: We study the non-linear corrections to the matter and velocity power spectra
in the synchronous gauge (SG). We consider the perturbations up to third order
in a zero-pressure fluid in flat cosmological background, which is relevant for
the non-linear growth of cosmic structure. As a result, we point out that the
SG is an inappropriate coordinate choice when handling the non-linear growth of
the large-scale structure. Although the equations in the SG happen to coincide
with those in the comoving gauge (CG) to linear order, they differ from second
order. In particular, the second order hydrodynamic equations in the the SG are
apparently in the Lagrangian form, whereas those in the CG are in the Eulerian
form. Thus, the non-linear power spectra naively presented in the original SG
show strange behavior quite different from the result of the Newtonian theory
even on sub-horizon scales. The power spectra in the SG show regularized
behaviors only after we introduce convective terms in the second order so that
the equations in two gauges coincide to the second order. |
Approximations for the divergence of the local large-scale structure
velocity field and its implications for Tilted Cosmology: We characterize the peculiar velocity field of the local large-scale
structure reconstructed from the $2M++$ survey, by treating it as a fluid,
extracting the divergence via different approximations over a range pf averaged
scales. This reconstructed field is important for cosmology, since it was used
to correct the peculiar redshifts of the last SNIA compilation Pantheon+. The
results have intriguing implications for the LLSS fluid dynamics and
particularly for the ``Tilted Cosmology'' model, although those results have to
be taken carefully as the velocity field could contain significant bias due to
the reconstruction procedure. Those possible bias and its influence in our
results are discussed. Representative values of the apparent deceleration
parameter ($\Tilde{q}$) are computed, in order to compare our results with the
theoretical predictions of the tilted-universe scenario. We conclude that
better velocity field reconstructions are necessary in order to constrain the
parameters implied in LLSS research and alternative cosmologies. | Dark Energy Survey Year 1 Results: Wide field mass maps via forward
fitting in harmonic space: We present new wide-field weak lensing mass maps for the Year 1 Dark Energy
Survey data, generated via a forward fitting approach. This method of producing
maps does not impose any prior constraints on the mass distribution to be
reconstructed. The technique is found to improve the map reconstruction on the
edges of the field compared to the conventional Kaiser-Squires method, which
applies a direct inversion on the data; our approach is in good agreement with
the previous direct approach in the central regions of the footprint. The
mapping technique is assessed and verified with tests on simulations; together
with the Kaiser-Squires method, the technique is then applied to data from the
Dark Energy Survey Year 1 data and the differences between the two methods are
compared. We also produce the first DES measurements of the convergence
Minkowski functionals and compare them to those measured in simulations. |
Clues on void evolution II: Measuring density and velocity profiles on
SDSS galaxy redshift space distortions: Using the redshift-space distortions of void-galaxy cross-correlation
function we analyse the dynamics of voids embedded in different environments.
We compute the void-galaxy cross-correlation function in the Sloan Digital Sky
Survey (SDSS) in terms of distances taken along the line of sight and projected
into the sky. We analyse the distortions on the cross-correlation isodensity
levels and we find anisotropic isocontours consistent with expansion for large
voids with smoothly rising density profiles and collapse for small voids with
overdense shells surrounding them. Based on the linear approach of
gravitational collapse theory we developed a parametric model of the
void-galaxy redshift space cross-correlation function. We show that this model
can be used to successfully recover the underlying velocity and density
profiles of voids from redshift space samples. By applying this technique to
real data, we confirm the twofold nature of void dynamics: large voids
typically are in an expansion phase whereas small voids tend to be surrounded
by overdense and collapsing regions. These results are obtained from the SDSS
spectroscopic galaxy catalogue and also from semi-analytic mock galaxy
catalogues, thus supporting the viability of the standard LCDM model to
reproduce large scale structure and dynamics. | Sensitivity of the Hydrogen Epoch of Reionization Array and its
Build-out Stages to One-point Statistics from Redshifted 21 cm Observations: We present a baseline sensitivity analysis of the Hydrogen Epoch of
Reionization Array (HERA) and its build-out stages to one-point statistics
(variance, skewness, and kurtosis) of redshifted 21 cm intensity fluctuation
from the Epoch of Reionization (EoR) based on realistic mock observations. By
developing a full-sky 21 cm lightcone model, taking into account the proper
field of view and frequency bandwidth, utilising a realistic measurement
scheme, and assuming perfect foreground removal, we show that HERA will be able
to recover statistics of the sky model with high sensitivity by averaging over
measurements from multiple fields. All build-out stages will be able to detect
variance, while skewness and kurtosis should be detectable for HERA128 and
larger. We identify sample variance as the limiting constraint of the variance
measurement while skewness and kurtosis measurements will be primarily limited
by thermal noise. The sensitivity can be improved by performing frequency
binning and windowing. In addition, we find that strong sample variance
fluctuation in the kurtosis measured from an individual field of observation
indicates the present of outlying cold or hot regions in the underlying
fluctuations, a feature that can potentially be used as an EoR bubble
indicator. This manuscript is altered from the originally published paper to
reflect corrections in the erratum. |
A Multiwavelength Study on the Fate of Ionizing Radiation in Local
Starbursts: The fate of ionizing radiation is vital for understanding cosmic ionization,
energy budgets in the interstellar and intergalactic medium, and star formation
rate indicators. The low observed escape fractions of ionizing radiation have
not been adequately explained, and there is evidence that some starbursts have
high escape fractions. We examine the spectral energy distributions of a sample
of local star-forming galaxies, containing thirteen local starburst galaxies
and ten of their ordinary star-forming counterparts, to determine if there
exist significant differences in the fate of ionizing radiation in these
galaxies. We find that the galaxy-to-galaxy variations in the SEDs is much
larger than any systematic differences between starbursts and non-starbursts.
For example, we find no significant differences in the total absorption of
ionizing radiation by dust, traced by the 24um, 70um, and 160um MIPS bands of
the Spitzer Space Telescope, although the dust in starburst galaxies appears to
be hotter than that of non-starburst galaxies. We also observe no excess
ultraviolet flux in the GALEX bands that could indicate a high escape fraction
of ionizing photons in starburst galaxies. The small H-alpha fractions of the
diffuse, warm ionized medium in starburst galaxies are apparently due to
temporarily boosted H-alpha luminosity within the star-forming regions
themselves, with an independent, constant WIM luminosity. This independence of
the WIM and starburst luminosities contrasts with WIM behavior in non-starburst
galaxies and underscores our poor understanding of radiation transfer in both
ordinary and starburst galaxies. | Determining thermal dust emission from Planck HFI data using a sparse,
parametric technique: Context: The Planck data releases have provided the community with
sub-millimetre and radio observations of the full-sky at unprecedented
resolutions. We make use of the Planck 353, 545 and 857 GHz maps alongside the
IRAS 3000 GHz map. These maps contain information on the cosmic microwave
background (CMB), cosmic infrared background (CIB), extragalactic point sources
and diffuse thermal dust emission. Aims: We aim to determine the modified black
body (MBB) model parameters of thermal dust emission in total intensity and
produce all sky maps of pure thermal dust, having separated this Galactic
component from the CMB and CIB. Methods: This separation is completed using a
new, sparsity-based, parametric method which we refer to as premise. The method
comprises of three main stages: 1) filtering of the raw data to reduce the
effect of the CIB on the MBB fit. 2) fitting an MBB model to the filtered data
across super-pixels of various sizes determined by the algorithm itself and 3)
refining these super-pixel estimates into full resolution maps of the MBB
parameters. Results: We present our maps of MBB temperature, spectral index and
optical depth at 5 arcmin resolution and compare our estimates to those of
GNILC as well as the two-step MBB fit presented by the Planck collaboration in
2013. Conclusions: By exploiting sparsity we avoid the need for smoothing,
enabling us to produce the first full resolution MBB parameter maps from
intensity measurements of thermal dust emission.We consider the premise
parameter estimates to be competitive with the existing state-of-the-art
solutions, outperforming these methods within low signal-to-noise regions as we
account for the CIB without removing thermal dust emission through
over-smoothing. |
Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in
the Ring Galaxy AM0644-741: We combine data from the ATNF and the SEST to investigate the neutral ISM in
AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is
concentrated in the 42-kpc diameter starburst ring, but appears dominated by
atomic gas, with a global molecular fraction (f_mol) of only 7.9%. Apart from
the starburst peak, the gas ring is stable against the growth of gravitational
instabilities (Q_gas=2-7). Including stars lowers Q overall, but not enough to
make Q<1 everywhere. The ring's global star formation efficiency (SFE) appears
somewhat elevated, but varies around the ring by more than an order of
magnitude, peaking where star formation is most intense. AM0644-741's star
formation law is peculiar: HI follows a Schmidt law while H2 is uncorrelated
with SFR/area. Photodissociation models yield low volume densities in the ring,
particularly in the starburst quadrant (n~2 cm^-3), implying a warm neutral
medium dominated ISM. At the same time, the ring's pressure and ambient
far-ultraviolet radiation field lead to the expectation of a predominantly
molecular ISM. We argue that the ring's peculiar star formation law, n, SFE,
and f_mol result from the ISM's >100 Myr confinement time in the starburst
ring, which enhances the destructive effects of embedded massive stars and
supernovae. As a result, the ring's molecular ISM becomes dominated by small
clouds where star formation is most intense, causing H2 to be underestimated by
12CO line fluxes: in effect X(CO) >> X(Gal) despite the ring's solar
metallicity. The observed large HI component is primarily a low density
photodissociation product, i.e., a tracer rather than a precursor of massive
star formation. Such an "over-cooked" ISM may be a general characteristic of
evolved starburst ring galaxies. | Flying across Galaxy Clusters with Google Earth: additional imagery from
SDSS co-added data: Galaxy clusters are spectacular. We provide a Google Earth compatible imagery
for the deep co-added images from the Sloan Digital Sky Survey and make it a
tool for examing galaxy clusters. More details about how to get it can be found
from the following website: https://sites.google.com/site/geclusters/ |
Beyond y and μ: the shape of the CMB spectral distortions in the
intermediate epoch, 1.5x10^4 < z < 2x10^5: We calculate numerical solutions and analytic approximations for the
intermediate-type spectral distortions. Detection of a \mu-type distortion
(saturated comptonization) in the CMB will constrain the time of energy
injection to be at a redshift 2x10^6> z > 2x10^5, while a detection of a y-type
distortion (minimal comptonization) will mean that there was heating of CMB at
redshift z< 1.5x10^4. We point out that the partially comptonized spectral
distortions, generated in the redshift range 1.5x10^4 < z x 2x10^5, are much
richer in information than the pure y and \mu-type distortions. The spectrum
created during this period is intermediate between y and \mu-type distortions
and depends sensitively on the redshift of energy injection. These
intermediate-type distortions cannot be mimicked by a mixture of y and \mu-type
distortions at all frequencies and vice versa. The measurement of these
intermediate-type CMB spectral distortions has the possibility to constrain
precisely not only the amount of energy release in the early Universe but also
the mechanism, for example, particle annihilation and Silk damping can be
distinguished from particle decay. The intermediate-type distortion templates
and software code using these templates to calculate the CMB spectral
distortions for user-defined energy injection rate are made publicly available. | Constraints on primordial magnetic fields from the optical depth of the
cosmic microwave background: Damping of magnetic fields via ambipolar diffusion and decay of
magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the
intergalactic medium (IGM). Delayed recombination of hydrogen atoms in the IGM
yields an optical depth to scattering of the cosmic microwave background (CMB).
The optical depth generated at $z\gg 10$ does not affect the "reionization
bump" of the CMB polarization power spectrum at low multipoles, but affects the
temperature and polarization power spectra at high multipoles. Writing the
present-day energy density of fields smoothed over the damping scale at the
decoupling epoch as $\rho_{B,0}=B_{0}^2/2$, we constrain $B_0$ as a function of
the spectral index, $n_B$. Using the Planck 2013 likelihood code that uses the
Planck temperature and lensing data together with the WMAP 9-year polarization
data, we find the 95% upper bounds of $B_0<0.63$, 0.39, and 0.18~nG for
$n_B=-2.9$, $-2.5$, and $-1.5$, respectively. For these spectral indices, the
optical depth is dominated by dissipation of the decaying MHD turbulence that
occurs shortly after the decoupling epoch. Our limits are stronger than the
previous limits ignoring the effects of the fields on ionization history.
Inverse Compton scattering of CMB photons off electrons in the heated IGM
distorts the thermal spectrum of CMB. Our limits on $B_0$ imply that the
$y$-type distortion from dissipation of fields in the post decoupling era
should be smaller than $10^{-9}$, $4\times10^{-9}$, and $10^{-9}$,
respectively. |
CMB statistical isotropy confirmation at all scales using multipole
vectors: We present an efficient numerical code and conduct, for the first time, a
null and model-independent CMB test of statistical isotropy using Multipole
Vectors (MVs) at all scales. Because MVs are insensitive to the angular power
spectrum $C_\ell$, our results are independent from the assumed cosmological
model. We avoid a posteriori choices and use pre-defined ranges of scales
$\ell\in[2,30]$, $\ell\in[2,600]$ and $\ell\in[2,1500]$ in our analyses. We
find that all four masked Planck maps, from both 2015 and 2018 releases, are in
agreement with statistical isotropy for $\ell\in[2,30]$, $\ell\in[2,600]$. For
$\ell\in[2,1500]$ we detect anisotropies but this is indicative of simply the
anisotropy in the noise: there is no anisotropy for $\ell < 1300$ and an
increasing level of anisotropy at higher multipoles. Our findings of no
large-scale anisotropies seem to be a consequence of avoiding \emph{a
posteriori} statistics. We also find that the degree of anisotropy in the full
sky (i.e. unmasked) maps vary enormously (between less than 5 and over 1000
standard deviations) among the different mapmaking procedures and data
releases. | The Swift Gamma-Ray Burst redshift distribution: selection biases and
optical brightness evolution at high-z?: We employ realistic constraints on astrophysical and instrumental selection
effects to model the Gamma-Ray Burst (GRB) redshift distribution using {\it
Swift} triggered redshift samples acquired from optical afterglows (OA) and the
TOUGH survey. Models for the Malmquist bias, redshift desert, and the fraction
of afterglows missing because of host galaxy dust extinction, are used to show
how the "true" GRB redshift distribution is distorted to its presently observed
biased distribution. We also investigate another selection effect arising from
a correlation between $E_{{\rm iso}}$ and $L_{{\rm opt}}$. The analysis, which
accounts for the missing fraction of redshifts in the two data subsets, shows
that a combination of selection effects (both instrumental and astrophysical)
can describe the observed GRB redshift distribution. Furthermore, the observed
distribution is compatible with a GRB rate evolution that tracks the global
SFR, although the rate at high-$z$ cannot be constrained with confidence.
Taking selection effects into account, it is not necessary to invoke
high-energy GRB luminosity evolution with redshift to explain the observed GRB
rate at high-$z$. |
Not too big, not too small: the dark halos of the dwarf spheroidals in
the Milky Way: We present a new analysis of the Aquarius simulations done in combination
with a semi-analytic galaxy formation model. Our goal is to establish whether
the subhalos present in LCDM simulations of Milky Way-like systems could host
the dwarf spheroidal (dSph) satellites of our Galaxy. Our analysis shows that,
contrary to what has been assumed in most previous work, the mass profiles of
subhalos are generally not well fit by NFW models but that Einasto profiles are
preferred. We find that for shape parameters alpha = 0.2 - 0.5 and Vmax = 10 -
30 km/s there is very good correspondence with the observational constraints
obtained for the nine brightest dSph of the Milky Way. However, to explain the
internal dynamics of these systems as well as the number of objects of a given
circular velocity the total mass of the Milky Way should be ~ 8x10^11 Msun, a
value that is in agreement with many recent determinations, and at the low mass
end of the range explored by the Aquarius simulations. Our simulations show
important scatter in the number of bright satellites, even when the Aquarius
Milky Way-like hosts are scaled to a common mass, and we find no evidence for a
missing population of massive subhalos in the Galaxy. This conclusion is also
supported when we examine the dynamics of the satellites of M31. | Structure Formation and Backreaction in Growing Neutrino Quintessence: A dependence of the neutrino masses on the dark energy scalar field could
provide a solution to the why now problem of dark energy. The dynamics of the
resulting cosmological model, growing neutrino quintessence, include an
attractive force between neutrinos substantially stronger than gravity. We
present a comprehensive approach towards an understanding of the full
cosmological evolution including the formation of large-scale neutrino
structures. Important effects we account for are local variations in the dark
energy and the backreaction on the background evolution, as well as
relativistic neutrino velocities. For this aim, we develop a relativistic
N-body treatment of the neutrinos combined with an explicit computation of the
local quintessence field. At its current stage, the simulation method is
successful until z ~ 1 and reveals a rich phenomenology. We obtain a detailed
picture of the formation of large-scale neutrino structures and their influence
on the evolution of matter, dark energy, and the late-time expansion of the
universe. |
Scaling properties of cosmological axion strings: There has been recent interest in the evolution and cosmological consequences
of global axionic string networks, and in particular in the issue of whether or
not these networks reach the scale-invariant scaling solution that is known to
exist for the simpler Goto-Nambu and Abelian-Higgs string networks. This is
relevant for determining the amount and spectrum of axions they produce. We use
the canonical velocity-dependent one-scale model for cosmic defect network
evolution to study the evolution of these global networks, confirming the
presence of deviations to scale-invariant evolution and in agreement with the
most recent numerical simulations. We also quantify the cosmological impact of
these corrections and discuss how the model can be used to extrapolate the
results of numerical simulations, which have a limited dynamic range, to the
full cosmological evolution of the networks, enabling robust predictions of
their consequences. Our analysis suggests that around the QCD scale, when the
global string network is expected to disappear and produce most of the axions,
the number of global strings per Hubble patch should be around $\xi\sim4.2$,
but also highlights the need for additional high-resolution numerical
simulations. | Discovery of a diffuse optical line emitting halo in the core of the
Centaurus cluster of galaxies: Line emission outside the protection of the
filaments: We present the discovery of diffuse optical line emission in the Centaurus
cluster seen with the MUSE IFU. The unparalleled sensitivity of MUSE allows us
to detect the faint emission from these structures which extend well beyond the
bounds of the previously known filaments. Diffuse structures (emission
surrounding the filaments, a northern shell and an extended Halo) are detected
in many lines typical of the nebulae in cluster cores ([NII]$_{\lambda
6548\&6583}$ ,[SII]$_{\lambda 6716\&6731}$, [OI]$_{\lambda 6300}$,
[OIII]$_{\lambda 4959\&5007}$ etc.) but are more than an order of magnitude
fainter than the filaments, with the faint halo only detected through the
brightest line in the spectrum ([NII]$_{\lambda 6583}$). These structures are
shown to be kinematically distinct from the stars in the central galaxy and
have different physical and excitation states to the filaments. Possible
origins are discussed for each structure in turn and we conclude that shocks
and/or pressure imbalances are resulting in gas dispersed throughout the
cluster core, formed from either disrupted filaments or direct cooling, which
is not confined to the bright filaments. |
Large-scale clustering as a probe of the origin and the host environment
of fast radio bursts: We propose to use degree-scale angular clustering of fast radio bursts (FRBs)
to identify their origin and the host galaxy population. We study the
information content in autocorrelation of the angular positions and dispersion
measures (DM) and in cross-correlation with galaxies. We show that the
cross-correlation with Sloan Digital Sky Survey (SDSS) galaxies will place
stringent constraints on the mean physical quantities associated with FRBs. If
$\sim$10,000 FRBs are detected with $\lesssim \rm deg$ resolution in the SDSS
field, the clustering analysis with the intrinsic DM scatter of $100\, {\rm
pc}/{\rm cm}^3$ can constrain the global abundance of free electrons at $z\lt1$
and the large-scale bias of FRB host galaxies (the statistical relation between
the distribution of host galaxies and cosmic matter density field) with
fractional errors (with a $68\%$ confidence level) of $\sim10\%$ and
$\sim20\%$, respectively. The mean near-source dispersion measure and the delay
time distribution of FRB rates relative to the global star forming rate can be
also determined by combining the clustering and the probability distribution
function of DM. Our approach will be complementary to high-resolution ($\ll
{\rm deg}$) event localization using e.g., VLA and VLBI for identifying the
origin of FRBs and the source environment. We strongly encourage future
observational programs such as CHIME, UTMOST, and HIRAX to survey FRBs in the
SDSS field. | Estimates for the number of visible galaxy-spanning civilizations and
the cosmological expansion of life: If advanced civilizations appear in the universe with an ability and desire
to expand, the entire universe can become saturated with life on a short
timescale, even if such expanders appear rarely. Our presence in an apparently
untouched Milky Way thus constrains the appearance rate of galaxy-spanning
Kardashev type III (K3) civilizations, if it is assumed that some fraction of
K3 civilizations will continue their expansion at intergalactic distances. We
use this constraint to estimate the appearance rate of K3 civilizations for 81
cosmological scenarios by specifying the extent to which humanity is a
statistical outlier. We find that in nearly all plausible scenarios, the
distance to the nearest visible K3 is cosmological. In searches for K3 galaxies
where the observable range is limited, we also find that the most likely
detections tend to be expanding civilizations who have entered the observable
range from farther away. An observation of K3 clusters is thus more likely than
isolated K3 galaxies. |
Viable Intermediate Inflation in the Mimetic DBI Model: We study the intermediate inflation in the mimetic Dirac-Born-Infeld model.
By considering the scale factor as $a=a_{0}\exp(bt^{\beta})$, we show that in
some ranges of the intermediate parameters $b$ and $\beta$, the model is free
of the ghost and gradient instabilities. We study the scalar spectral index,
tensor spectral index, and the tensor-to-scalar ratio in this model and compare
the results with Planck2018 TT, TE, EE+lowE+lensing +BAO +BK14 data at $68\%$
and $95\%$ CL. In this regard, we find some constraints on the intermediate
parameters that lead to the observationally viable values of the perturbation
parameters. We also seek the non-gaussian features of the primordial
perturbations in the equilateral configuration. By performing the numerical
analysis on the nonlinearity parameter in this configuration, we show that the
amplitude of the non-gaussianity in the intermediate mimetic DBI model is
predicted to be in the range $-16.7<f^{equil}<-12.5$. We show that, with
$0<b\leq 10$ and $0.345<\beta<0.387$, we have an instabilities-free
intermediate mimetic DBI model that gives the observationally viable
perturbation and non-gaussianity parameters. | The GAMA Panchromatic Survey: The Galaxy And Mass Assembly Survey (GAMA) has now been operating for almost
5 years gathering spectroscopic redshifts for five regions of sky spanning 300
sq degrees in total to a depth of r<19.8 mag. The survey has amassed over
225,000 redshifts making it the third largest redshift campaign after the SDSS
and BOSS surveys. The survey has two novel features that set it apart: (1)
complete and uniform sampling to a fixed flux limit (r<19.8 mag) regardless of
galaxy clustering due to multiple-visits to each sky region, enabling the
construction of high-fidelity catalogues of groups and pairs, (2) co-ordination
with diverse imaging campaigns which together sample an extremely broad range
along the electro-magnetic spectrum from the UV (GALEX) through optical (VST
KIDs), near-IR (VISTA VIKING), mid-IR (WISE), far-IR (Herschel-Atlas), 1m
(GMRT), and eventually 20cm continuum and rest-frame 21cm line measurements
(ASKAP DINGO). Apart from the ASKAP campaign all multi-wavelength programmes
are either complete or in the final stages of observations and the UV-far-IR
data are expected to be fully merged by the end of 2013. This article provides
a brief flavour of the coming panchromatic database which will eventually
include measurements or upper-limits across 27 wavebands for 380,000 galaxies.
GAMA DR2 is scheduled for the end of January 2013. |
Impact of Warm Dark Matter on the Cosmic Neutrino Background
Anisotropies: The Cosmic Neutrino Background (C$\nu$B) anisotropies for massive neutrinos
are a unique probe of large-scale structure formation. The redshift-distance
measure is completely different for massive neutrinos as compared to
electromagnetic radiation. The C$\nu$B anisotropies in massive neutrinos grow
in response to non-relativistic motion in gravitational potentials seeded by
relatively high $k$-modes. Differences in the early phases of large-scale
structure formation in Warm Dark Matter (WDM) versus Cold Dark Matter (CDM)
cosmologies have an impact on the magnitude of the C$\nu$B anisotropies for
contributions to the angular power spectrum that peak at high $k$-modes. We
take the examples of WDM consisting of 2, 3 or 7 keV sterile neutrinos and show
that the C$\nu$B anisotropies for 0.05 eV neutrinos drop off at high-$l$
multipole moment in the angular power spectrum relative to CDM. At the same
angular scales that one can observe baryonic acoustical oscillations in the
CMB, the C$\nu$B anisotropies begin to become sensitive to differences in WDM
and CDM cosmologies. The precision measurement of high-$l$ multipoles in the
C$\nu$B neutrino sky map is a potential possibility for the PTOLEMY experiment
with thin film targets of spin-polarized atomic tritium superfluid that exhibit
significant quantum liquid amplification for non-relativistic relic neutrino
capture. | Improved Limits on Spin-Dependent WIMP-Proton Interactions from a Two
Liter CF$_3$I Bubble Chamber: Data from the operation of a bubble chamber filled with 3.5 kg of CF$_{3}$I
in a shallow underground site are reported. An analysis of ultrasound signals
accompanying bubble nucleations confirms that alpha decays generate a
significantly louder acoustic emission than single nuclear recoils, leading to
an efficient background discrimination. Three dark matter candidate events were
observed during an effective exposure of 28.1 kg-day, consistent with a neutron
background. This observation provides the strongest direct detection constraint
to date on WIMP-proton spin-dependent scattering for WIMP masses $>20$
GeV/c$^{2}$. |
Scalar models for the unification of the dark sector: We review the difficulties of the generalized Chaplygin gas model to fit
observational data, due to the tension between background and perturbative
tests. We argue that such issues may be circumvented by means of a
self-interacting scalar field representation of the model. However, this
proposal seems to be successful only if the self-interacting scalar field has a
non-canonical form. The latter can be implemented in Rastall's theory of
gravity. | From Planck data to Planck era: Observational tests of Holographic
Cosmology: We test a class of holographic models for the very early universe against
cosmological observations and find that they are competitive to the standard
$\Lambda$CDM model of cosmology. These models are based on three dimensional
perturbative super-renormalizable Quantum Field Theory (QFT), and while they
predict a different power spectrum from the standard power-law used in
$\Lambda$CDM, they still provide an excellent fit to data (within their regime
of validity). By comparing the Bayesian evidence for the models, we find that
$\Lambda$CDM does a better job globally, while the holographic models provide a
(marginally) better fit to data without very low multipoles (i.e. $l\lesssim
30$), where the dual QFT becomes non-perturbative. Observations can be used to
exclude some QFT models, while we also find models satisfying all
phenomenological constraints: the data rules out the dual theory being
Yang-Mills theory coupled to fermions only, but allows for Yang-Mills theory
coupled to non-minimal scalars with quartic interactions. Lattice simulations
of 3d QFT's can provide non-perturbative predictions for large-angle statistics
of the cosmic microwave background, and potentially explain its apparent
anomalies. |
Characterizing the linear growth rate of cosmological density
perturbations in an f(R) model: We investigate the linear growth rate of cosmological matter density
perturbations of a viable f(R) model both numerically and analytically. We find
that the growth rate in the scalar-tensor regime can be characterized by a
simple analytic formula. We also investigate a prospect of constraining the
Compton wavelength scale of the f(R) model with a future weak lensing survey. | A tentative derivation of the main cosmological parameters: Based on the assumption that some apparent properties of the observable
universe are accurate at a reasonable level of approximation, a tentative is
made to independently derive the values of the baryon density parameter, the
Hubble constant, the cosmic microwave background temperature and the helium
mass fraction. The obtained values are in excellent agreement with those given
by the most recent observational data. |
Are $H_0$ and $σ_8$ tensions generic to present cosmological data?: Yes, for a wide range of cosmological models ($\Lambda$CDM, non-interacting
$w_z$CDM or models with possible interactions between dark energy and dark
matter, in either phantom or non-phantom regimes). In the recent past there
have been many attempts to solve the tension between direct measurements of
$H_0$ and $\sigma_8 \sqrt{\Omega_{0 {\rm m}}}$ from the respective low redshift
observables and indirect measurements of these quantities from the cosmic
microwave background (CMB). In this work we reconstruct a model independent
approach that boils down to different classes of cosmological models under
suitable parameters choices. We test this parameterization against the latest
Planck CMB data combined with recent BAO, SNeIa datasets and the R16 direct
$H_0$ measurements, and compare among different cosmological models. Our
analysis reveals that a strong positive correlation between $H_0$ and
$\sigma_8$ is more or less generic, irrespective of the choice of cosmological
models. We also find that present data slightly prefers a phantom equation of
state for dark energy and a slight negative value for effective equation of
state for dark matter (which is a direct signature of interacting models) with
a relatively high value for $H_0$ consistent with R16 and simultaneously, a
consistent value for $\Omega_{0 {\rm m}}$. Thus, even though the tensions
cannot be fully resolved, interacting models with phantom equation of state get
a slight edge over the others for currently available data. We also see that
allowing interaction between dark energy and dark matter may resolve the
tension between the high redshift CMB data and individual low redshift
datasets, but the low redshift datasets have inconsistencies between them (e.g.
between BAO and $H_0$, SNeIa and BAO, and cluster counts and $H_0$) that are
practically independent of the cosmological model. | An Analytic Formulation of 21-cm Signal from Early Phase of Epoch of
Reionization: We present an analytic formulation to model the fluctuating component of the
HI signal from the epoch of reionization during the phase of partial heating.
During this phase, we assume self-ionized regions, whose size distribution can
be computed using excursion set formalism, to be surrounded by heated regions.
We model the evolution of heating profile around these regions (near zone) and
their merger into the time-dependent background (far zone). We develop a
formalism to compute the two-point correlation function for this topology,
taking into account the heating auto-correlation and heating-ionization
cross-correlation. We model the ionization and X-ray heating using four
parameters: efficiency of ionization, $\zeta$, number of X-ray photons per
stellar baryon, $N_{\rm heat}$, the spectral index of X-ray photons, $\alpha$,
and the minimum frequency of X-ray photons, $\nu_{\rm min}$. We compute the HI
signal in the redshift range $10 < z < 20$ for the $\Lambda$CDM model for a set
of these parameters. We show that the HI signal for a range of scales
$1\hbox{-}8 \, \rm Mpc$ show a peak strength $100\hbox{-}1000 \, \rm (mK)^2$
during the partially heated era. The redshift at which the signal makes a
transition to uniformly heated universe depends on modelling parameters, e.g.
if $\nu_{\rm min}$ is changed from $100 \, \rm eV$ to $1 \, \rm keV$, this
transition moves from $z \simeq 15$ to $z \simeq 12$. This result, along with
the dependence of the HI signal on modelling parameters, is in reasonable
agreement with existing results from N-body simulations. |
Optical spectral index - luminosity relation for the 17 mapped
Palomar-Green quasars: In this paper, the optical spectra index - luminosity relationship is checked
for the well-known 17 individual mapped QSOs, in order to give one more clearer
conclusion on the so far conflicting dependence of the spectral index on the
luminosity for AGN. Different from the global relationships based on the color
difference (photometry parameters) for samples of AGN, the more reliable
relationship is determined for the multi-epoch observed individual mapped QSOs
with no contamination from the host galaxies, the line variabilities and the
much different central properties. The final confirmed results are as follows.
(1): No strong dependence of the optical spectral index on the continuum
luminosity can be found for all the 17 QSOs, besides two objects (PG 0026 and
PG 1613) having some weak trends (with $3\sigma$ confidence level) for the
relationship. In other words, the common sense 'AGNs get bluer when they get
brighter' is not so common. (2): There are much different damped intrinsic
variability time scales for the variability modes of the optical spectral index
and the continuum emission, through the well applied Damped Random Walk method
for the AGN variability. In other words, there are some different intrinsic
mechanisms controlling the variabilities of the optical spectral index and the
power law AGN continuum emission. Therefore, the much weak dependence of the
optical spectral index on the continuum luminosity can be further confirmed. | The M_bh-sigma diagram, and the offset nature of barred active galaxies: From a sample of 50 predominantly inactive galaxies with direct supermassive
black hole mass measurements, it has recently been established that barred
galaxies tend to reside rightward of the M_bh-sigma relation defined by
non-barred galaxies. Either black holes in barred galaxies tend to be anaemic
or the central velocity dispersions in these galaxies have a tendency to be
elevated by the presence of the bar. The latter option is in accord with
studies connecting larger velocity dispersions in galaxies with old bars, while
the former scenario is at odds with the observation that barred galaxies do not
deviate from the M_bh-luminosity relation. Using a sample of 88 galaxies with
active galactic nuclei, whose supermassive black hole masses have been
estimated from their associated emission lines, we reveal for the first time
that they also display this same general behavior in the M_bh-sigma diagram
depending on the presence of a bar or not. A new symmetrical and
non-symmetrical "barless" M_bh-sigma relation is derived using 82 non-barred
galaxies. The barred galaxies are shown to reside on or up to ~1 dex below this
relation. This may explain why narrow-line Seyfert 1 galaxies appear offset
from the "barless" M_bh-sigma relation, and has far reaching implications given
that over half of the disk galaxy population are barred. |
Analytical model for non-thermal pressure in galaxy clusters - III.
Removing the hydrostatic mass bias: Non-thermal pressure in galaxy clusters leads to underestimation of the mass
of galaxy clusters based on hydrostatic equilibrium with thermal gas pressure.
This occurs even for dynamically relaxed clusters that are used for calibrating
the mass-observable scaling relations. We show that the analytical model for
non-thermal pressure developed in Shi & Komatsu 2014 can correct for this
so-called 'hydrostatic mass bias', if most of the non-thermal pressure comes
from bulk and turbulent motions of gas in the intracluster medium. Our
correction works for the sample average irrespective of the mass estimation
method, or the dynamical state of the clusters. This makes it possible to
correct for the bias in the hydrostatic mass estimates from X-ray surface
brightness and the Sunyaev-Zel'dovich observations that will be available for
clusters in a wide range of redshifts and dynamical states. | Infrared photometry of Young Massive Clusters in the starburst galaxy
NGC 4214: We present the results of an infrared photometric survey performed with
NICS@TNG in the nearby starburst galaxy NGC 4214. We derived accurate
integrated JK magnitudes of 10 young massive clusters and compared them with
the already available Hubble Space Telescope ultraviolet colors. These clusters
are located in the combined ultraviolet-infrared colors planes on well defined
sequences, whose shapes allow a precise determination of their age. By means of
the comparison with suitable stellar evolution models we estimated ages,
metallicities, reddening and masses of these clusters. All the analyzed
clusters appear to be younger than log(t/yr)<8.4, moderately metal-rich and
slightly less massive than present-day Galactic globular clusters. The derived
ages for clusters belonging to the secondary HII star forming complex are
significantly larger than those previously estimated in the literature. We also
discuss the possibility of using the ultraviolet-infrared color-color diagram
to select candidate young massive clusters hosting multiple stellar
populations. |
Spectral variability of quasars from multi-epoch photometric data in the
Sloan Digital Sky Survey Stripe 82: We present a new approach to analysing the dependence of quasar variability
on rest-frame wavelengths. We exploited the spectral archive of the Sloan
Digital Sky Survey (SDSS) to create a sample of more than 9000 quasars in the
Stripe 82. The quasar catalogue was matched with the Light Motion Curve
Catalogue for SDSS Stripe 82 and individual first-order structure functions
were computed. The structure functions are used to create a variability
indicator that is related to the same intrinsic timescales for all quasars (1
to 2 yr in the rest frame). We study the variability ratios for adjacent SDSS
filter bands as a function of redshift. While variability is almost always
stronger in the bluer passband compared to the redder, the variability ratio
depends on whether strong emission lines contribute to either one band or the
other. The variability ratio-redshift relations resemble the corresponding
colour index-redshift relations. From the comparison with Monte Carlo
simulations of variable quasar spectra we find that the observed variability
ratio-redshift relations are closely fitted assuming that (a) the r.m.s.
fluctuation of the quasar continuum follows a power law-dependence on the
intrinsic wavelength with an exponent -2 (i.e., bluer when brighter) and (b)
the variability of the emission line flux is only about 10% of that of the
underlying continuum. These results, based upon the photometry of more than
8000 quasars, confirm the previous findings by Wilhite et al. (2005) from 315
quasars with repeated SDSS spectroscopy. Finally, we find that quasars with
unusual spectra and weak emission lines tend to have less variability than
conventional quasars. This trend is opposite to what is expected from the
dilution effect of variability due to line emission and may be indicative of
high Eddington ratios in these unconventinal quasars. | Influence of the turbulent motion on the chiral magnetic effect in the
early Universe: We study the magnetohydrodynamics of relativistic plasmas accounting for the
chiral magnetic effect (CME). To take into account the evolution of the plasma
velocity, obeying the Navier-Stokes equation, we approximate it by the Lorentz
force accompanied by the phenomenological drag time parameter. On the basis of
this ansatz, we obtain the contributions of both the turbulence effects,
resulting from the dynamo term, and the magnetic field instability, caused by
the CME, to the evolution of the magnetic field governed by the modified
Faraday equation. In this way, we explore the evolution of the magnetic field
energy and the magnetic helicity density spectra in the early Universe plasma.
We find that the right-left electron asymmetry is enhanced by the turbulent
plasma motion in a strong seed magnetic field compared to the pure the CME case
studied earlier for the hot Universe plasma in the same broken phase. |
Physical properties underlying observed kinematics of satellite galaxies: We study the kinematics of satellites around isolated galaxies selected from
the Sloan Digital Sky Survey (SDSS) spectroscopic catalog. Using a model of the
phase-space density previously measured for the halos of LCDM dark matter
cosmological simulations, we determine the properties of the halo mass
distribution and the orbital anisotropy of the satellites as a function of the
colour-based morphological type and the stellar mass of the central host
galaxy. We place constraints on the halo mass and the concentration parameter
of dark matter and the satellite number density profiles. We obtain a
concentration-mass relation for galactic dark matter haloes that is consistent
with predictions of a standard LCDM cosmological model. At given halo or
stellar mass, red galaxies have more concentrated halos than their blue
counterparts. The fraction of dark matter within a few effective radii is
minimal for 11.25<log M_star<11.5. The number density profile of the satellites
appears to be shallower than of dark matter, with the scale radius typically 60
per cent larger than of dark matter. The orbital anisotropy around red hosts
exhibits a mild excess of radial motions, in agreement with the typical
anisotropy profiles found in cosmological simulations, whereas blue galaxies
are found to be consistent with an isotropic velocity distribution. Our new
constraints on the halo masses of galaxies are used to provide analytic
approximations of the halo-to-stellar mass relation for red and blue galaxies. | Thermal Inflation with a Thermal Waterfall Scalar Field Coupled to a
Light Spectator Scalar Field: This thesis begins with an introduction to the state of the art of modern
Cosmology. The field of Particle Cosmology is then introduced and explored, in
particular with regard to the study of cosmological inflation. We then
introduce a new model of Thermal Inflation, in which the mass of the thermal
waterfall field responsible for the inflation is dependent on a light spectator
scalar field. The model contains a variety of free parameters, two of which
control the power of the coupling term and the non-renormalizable term. We use
the $\delta N$ formalism to investigate the "end of inflation" and modulated
decay scenarios in turn to see whether they are able to produce the dominant
contribution to the primordial curvature perturbation $\zeta$. We constrain the
model and then explore the parameter space. We explore key observational
signatures, such as non-Gaussianity, the scalar spectral index and the running
of the scalar spectral index. We find that for some regions of the parameter
space, the ability of the model to produce the dominant contribution to $\zeta$
is excluded. However, for other regions of the parameter space, we find that
the model yields a sharp prediction for a variety of parameters within the
model. |
The Zurich Environmental Study (ZENS) of Galaxies in Groups along the
Cosmic Web. I. Which Environment Affects Galaxy Evolution?: The Zurich Environmental Study (ZENS) is based on a sample of ~1500 galaxy
members of 141 groups in the mass range ~10^12.5-14.5 M_sun within the narrow
redshift range 0.05<z<0.0585. ZENS adopts novel approaches, here described, to
quantify four different galactic environments, namely: (1) the mass of the host
group halo; (2) the projected halo-centric distance; (3) the rank of galaxies
as central or satellites within their group halos; and (4) the filamentary
large-scale structure (LSS) density. No self-consistent identification of a
central galaxy is found in ~40% of <10^13.5 M_sun groups, from which we
estimate that ~15% of groups at these masses are dynamically unrelaxed systems.
Central galaxies in relaxed and unrelaxed groups have in general similar
properties, suggesting that centrals are regulated by their mass and not by
their environment. Centrals in relaxed groups have however ~30% larger sizes
than in unrelaxed groups, possibly due accretion of small satellites in
virialized group halos. At M>10^10 M_sun, satellite galaxies in relaxed and
unrelaxed groups have similar size, color and (specific) star formation rate
distributions; at lower galaxy masses, satellites are marginally redder in
relaxed relative to unrelaxed groups, suggesting quenching of star formation in
low-mass satellites by physical processes active in relaxed halos. Finally,
relaxed and unrelated groups show similar stellar mass conversion efficiencies,
peaking at halo masses around 10^12.5 M_sun. In the enclosed ZENS catalogue we
publish all environmental diagnostics as well as the galaxy structural and
photometric measurements described in companion ZENS papers II and III. | Identification of Superclusters and their Properties in the Sloan
Digital Sky Survey Using WHL Cluster Catalog: Superclusters are the largest massive structures in the cosmic web on tens to
hundreds of megaparsecs (Mpc) scales. They are the largest assembly of galaxy
clusters in the Universe. Apart from a few detailed studies of such structures,
their evolutionary mechanism is still an open question. In order to address and
answer the relevant questions, a statistically significant, large catalog of
superclusters covering a wide range of redshifts and sky areas is essential.
Here, we present a large catalog of 662 superclusters identified using a
modified $\textit{ Friends of Friends}$ algorithm applied on the WHL
(Wen-Han-Liu) cluster catalog within a redshift range of $0.05 \le z \le 0.42$.
We name the most massive supercluster at $z \sim 0.25$ as $\textit{Einasto
Supercluster}$. We find that the median mass of superclusters is $\sim 5.8
\times 10^{15}$ M$_{\odot}$ and median size $\sim 65$ Mpc. We find that the
supercluster environment slightly affects the growth of clusters. We compare
the properties of the observed superclusters with the mock superclusters
extracted from the Horizon Run 4 cosmological simulation. The properties of
superclusters in mocks and observations are in broad agreement. We find that
the density contrast of a supercluster is correlated with its maximum extent
with a power law index, $\alpha \sim -2$. The phase-space distribution of mock
superclusters shows that, on average, $\sim 90\%$ part of a supercluster has a
gravitational influence on its constituents. We also show mock halos' average
number density and peculiar velocity profiles in and around the superclusters. |
Morphology in the Era of Large Surveys: The study of galaxies has changed dramatically over the past few decades with
the advent of large-scale astronomical surveys. These large collaborative
efforts have made available high-quality imaging and spectroscopy of hundreds
of thousands of systems, providing a body of observations which has
significantly enhanced our understanding not only of cosmology and large-scale
structure in the universe but also of the astrophysics of galaxy formation and
evolution. Throughout these changes, one thing that has remained constant is
the role of galaxy morphology as a clue to understanding galaxies. But
obtaining morphologies for large numbers of galaxies is challenging; this
topic, "Morphology in the era of large surveys", was the subject of a recent
discussion meeting at the Royal Astronomical Society, and this "Astronomy and
Geophysics" article is a report on that meeting. | Direct tests of General Relativity under screening effect with
galaxy-scale strong lensing systems: Observations of galaxy-scale strong gravitational lensing (SGL) systems have
enabled unique tests of nonlinear departures from general relativity (GR) on
the galactic and supergalactic scales. One of the most important cases of such
tests is constraints on the gravitational slip between two scalar gravitational
potentials. In this paper, we use a newly compiled sample of strong
gravitational lenses to test the validity of GR, focusing on the screening
effects on the apparent positions of lensed sources relative to the GR
predictions. This is the first simultaneous measurement of the Post-Newtonian
(PN) parameter ($\gamma_{PN}$) and the screening radius ($\Lambda$) without any
assumptions about the contents of the Universe. Our results suggest that the
measured PPN is marginally consistent with GR ($\gamma_{PN}=1$) with increasing
screening radius ($\Lambda = 10-300 $kpc), although the choice of lens models
may have a significant influence on the final measurements. Based on a
well-defined sample of 5000 simulated strong lenses from the forthcoming LSST,
our methodology will provide a strong extragalactic test of GR with an accuracy
of 0.5\%, assessed up to scales of $\Lambda \sim 300$ kpc. For the current and
future observations of available SGL systems, there is no noticeable evidence
indicating some specific cutoff scales on kpc-Mpc scales, beyond which new
gravitational degrees of freedom are expressed. |
Probing galaxy assembly bias with LRG weak lensing observations: In Montero-Dorta et al. 2017, we show that luminous red galaxies (LRGs) from
the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at $z\sim0.55$ can
be divided into two groups based on their star formation histories. So-called
fast-growing LRGs assemble $80\%$ of their stellar mass at $z\sim5$, whereas
slow-growing LRGs reach the same evolutionary state at $z\sim1.5$. We further
demonstrate that these two subpopulations present significantly different
clustering properties on scales of $\sim1 - 30 \mathrm{Mpc}$. Here, we measure
the mean halo mass of each subsample using the galaxy-galaxy lensing technique,
in the $\sim190\deg^2$ overlap of the LRG catalogue and the CS82 and CFHTLenS
shear catalogues. We show that fast- and slow-growing LRGs have similar lensing
profiles, which implies that they live in haloes of similar mass:
$\log\left(M_{\rm halo}^{\rm fast}/h^{-1}\mathrm{M}_{\odot}\right) =
12.85^{+0.16}_{-0.26}$ and $\log\left(M_{\rm halo}^{\rm
slow}/h^{-1}\mathrm{M}_{\odot}\right) =12.92^{+0.16}_{-0.22}$. This result,
combined with the clustering difference, suggests the existence of galaxy
assembly bias, although the effect is too subtle to be definitively proven
given the errors on our current weak-lensing measurement. We show that this can
soon be achieved with upcoming surveys like DES. | Constraining Primordial Black-Hole Bombs through Spectral Distortions of
the Cosmic Microwave Background: We consider the imprint of superradiant instabilities of nonevaporating
primordial black holes (PBHs) on the spectrum of the cosmic microwave
background (CMB). In the radiation dominated era, PBHs are surrounded by a
roughly homogeneous cosmic plasma which endows photons with an effective mass
through the plasma frequency. In this setting, spinning PBHs are unstable to a
spontaneous spindown through the well-known "black-hole bomb" mechanism. At
linear level, the photon density is trapped by the effective photon mass and
grows exponentially in time due to superradiance. As the plasma density
declines due to cosmic expansion, the associated energy around PBHs is released
and dissipated in the CMB. We evaluate the resulting spectral distortions of
the CMB in the redshift range 10^3 < z < 2x10^6. Using the existing COBE/FIRAS
bounds on CMB spectral distortions, we derive upper limits on the fraction of
dark matter that can be associated with spinning PBHs in the mass range
10^{-8}*Msun < M < 0.2*Msin. For maximally-spinning PBHs, our limits are much
tighter than those derived from microlensing or other methods. Future data from
the proposed PIXIE mission could improve our limits by several orders of
magnitude. |
Massive Fields as Systematics for Single Field Inflation: During inflation, massive fields can contribute to the power spectrum of
curvature perturbation via a dimension-5 operator. This contribution can be
considered as a bias for the program of using $n_s$ and $r$ to select inflation
models. Even the dimension-5 operator is suppressed by $\Lambda = M_p$, there
is still a significant shift on the $n_s$-$r$ diagram if the massive fields
have $m\sim H$. On the other hand, if the heavy degree of freedom appears only
at the same energy scale as the suppression scale of the dimension-5 operator,
then significant shift on the $n_s$-$r$ diagram takes place at $m=\Lambda \sim
70H$, which is around the inflationary time-translation symmetry breaking
scale. Hence, the systematics from massive fields pose a greater challenge for
future high precision experiments for inflationary model selection. This result
can be thought of as the impact of UV sensitivity to inflationary observables. | MADLens, a python package for fast and differentiable non-Gaussian
lensing simulations: We present MADLens a python package for producing non-Gaussian lensing
convergence maps at arbitrary source redshifts with unprecedented precision.
MADLens is designed to achieve high accuracy while keeping computational costs
as low as possible. A MADLens simulation with only $256^3$ particles produces
convergence maps whose power agree with theoretical lensing power spectra up to
$L{=}10000$ within the accuracy limits of HaloFit. This is made possible by a
combination of a highly parallelizable particle-mesh algorithm, a sub-evolution
scheme in the lensing projection, and a machine-learning inspired sharpening
step. Further, MADLens is fully differentiable with respect to the initial
conditions of the underlying particle-mesh simulations and a number of
cosmological parameters. These properties allow MADLens to be used as a forward
model in Bayesian inference algorithms that require optimization or
derivative-aided sampling. Another use case for MADLens is the production of
large, high resolution simulation sets as they are required for training novel
deep-learning-based lensing analysis tools. We make the MADLens package
publicly available under a Creative Commons License
(https://github.com/VMBoehm/MADLens). |
The Galaxy Stellar Mass Function of X-ray detected groups: environmental
dependence of galaxy evolution in the COSMOS survey: We study the stellar mass distribution for galaxies in 160 X-ray detected
groups of 10^13<Log(M_200/M_sun)<2x10^14 and compare it with that of galaxies
in the field, to investigate the action of environment on the build up of the
stellar mass. We highlight differences in the build up of the passive
population in the field, which imprint features in the distribution of stellar
mass of passive galaxies at Log(M/M_sun)< 10.5. The gradual diminishing of the
effect when moving to groups of increasing total masses indicates that the
growing influence of the environment in bound structures is responsible for the
build up of a quenched component at Log(M/M_sun)< 10.5. Differently, the
stellar mass distribution of star forming galaxies is similar in shape in all
the environments, and can be described by a single Schechter function both in
groups and in the field. Little evolution is seen up to redshift 1.
Nevertheless at z=0.2-0.4 groups with M_200<6x10^13 Msun (low mass groups) tend
to have a characteristic mass for star forming galaxies which is 50% higher
than in higher mass groups; we interpret it as a reduced action of
environmental processes in such systems. Furthermore we analyse the
distribution of sSFR--Log(M) in groups and in the field, and find that groups
show on average a lower sSFR (by ~0.2 dex) at z<0.8. Accordingly, we find that
the fraction of star forming galaxies is increasing with redshift in all
environments, but at a faster pace in the denser ones. Finally our analysis
highlights that low mass groups have a higher fraction (by 50%) of the stellar
mass locked in star forming galaxies than higher mass systems (i.e. 2/3 of
their stellar mass). | Testing the Copernican Principle with Hubble Parameter: Using the longitudinal expression of Hubble expansion rate for the general
Lema\^itre-Tolman-Bondi (LTB) metric as a function of cosmic time, we examine
the scale on which the Copernican Principle holds in the context of a void
model. By way of performing parameter estimation on the CGBH void model, we
show that the Hubble parameter data favors a void with characteristic radius of
2 ~ 3 Gpc. This brings the void model closer, but not yet enough, to harmony
with observational indications given by the background kinetic
Sunyaev-Zel'dovich effect and the normalization of near-infrared galaxy
luminosity function. However, the test of such void models may ultimately lie
in the future detection of the discrepancy between longitudinal and transverse
expansion rates, a touchstone of inhomogeneous models. With the proliferation
of observational Hubble parameter data and future large-scale structure
observation, a definitive test could be performed on the question of cosmic
homogeneity. Particularly, the spherical LTB void models have been ruled out,
but more general non-spherical inhomogeneities still need to be tested by
observation. In this paper, we utilise a spherical void model to provide
guidelines into how observational tests may be done with more general models in
the future. |
An analytical method to simulate the HI 21-cm visibility signal for
intensity mapping experiments: Simulations play a vital role in testing and validating HI 21-cm power
spectrum estimation techniques. Conventional methods use techniques like N-body
simulations to simulate the sky signal which is then passed through a model of
the instrument. This makes it necessary to simulate the HI distribution in a
large cosmological volume, and incorporate both the light-cone effect and the
telescope's chromatic response. The computational requirements may be
particularly large if one wishes to simulate many realizations of the signal.
In this paper we present an analytical method to simulate the HI visibility
signal. This is particularly efficient if one wishes to simulate a large number
of realizations of the signal. Our method is based on theoretical predictions
of the visibility correlation which incorporate both the light-cone effect and
the telescope's chromatic response. We have demonstrated this method by
applying it to simulate the HI visibility signal for the upcoming Ooty Wide
Field Array Phase I. | The shape distribution of superclusters in SDSS DR 12: Galaxy superclusters, the largest galaxy structures in the cosmic web, are
formed due to the gravitational collapse (although they are not usually
gravitationally bound). Their geometrical properties can shed light on the
structure formation process on cosmological scales, hence on the fundamental
properties of gravity itself. In this work we study the distributions of the
shape, topology and morphology of the superclusters extracted from SDSS DR 12
main galaxy sample and defined in two different ways - using fixed and adaptive
density threshold in the luminosity-density field. To assess the geometry and
topology of each individual supercluster, we employ Minkowski functionals and
Shapefinders, precisely calculated by the shape diagnostic tool SURFGEN2. Both
supercluster samples produce similar shape distributions. Not surprisingly,
most superclusters are spherical in shape with trivial topology. However, large
superclusters with volumes $V \gtrsim 10^{4}$ Mpc$^{3}$ are statistically found
to be filamentary with non-zero genus values. The results, shape distributions
and catalogues have been made publicly available. |
Inhomogeneous cosmological models: exact solutions and their
applications: Recently, inhomogeneous generalisations of the
Friedmann-Lemaitre-Robertson-Walker cosmological models have gained interest in
the astrophysical community and are more often employed to study cosmological
phenomena. However, in many papers the inhomogeneous cosmological models are
treated as an alternative to the FLRW models. In fact, they are not an
alternative, but an exact perturbation of the latter, and are gradually
becoming a necessity in modern cosmology. The assumption of homogeneity is just
a first approximation introduced to simplify equations. So far this assumption
is commonly believed to have worked well, but future and more precise
observations will not be properly analysed unless inhomogeneities are taken
into account. This paper reviews recent developments in the field and shows the
importance of an inhomogeneous framework in the analysis of cosmological
observations. | CosmoPMC: Cosmology Population Monte Carlo: We present the public release of the Bayesian sampling algorithm for
cosmology, CosmoPMC (Cosmology Population Monte Carlo). CosmoPMC explores the
parameter space of various cosmological probes, and also provides a robust
estimate of the Bayesian evidence. CosmoPMC is based on an adaptive importance
sampling method called Population Monte Carlo (PMC). Various cosmology
likelihood modules are implemented, and new modules can be added easily. The
importance-sampling algorithm is written in C, and fully parallelised using the
Message Passing Interface (MPI). Due to very little overhead, the wall-clock
time required for sampling scales approximately with the number of CPUs. The
CosmoPMC package contains post-processing and plotting programs, and in
addition a Monte-Carlo Markov chain (MCMC) algorithm. The sampling engine is
implemented in the library pmclib, and can be used independently. The software
is available for download at http://www.cosmopmc.info. |
Explosive phenomena in modified gravity: Observational manifestations of some models of modified gravity, which have
been suggested to explain the accelerated cosmological expansion, are analyzed
for gravitating systems with time dependent mass density. It is shown that if
the mass density rises with time, the system evolves to the singular state with
infinite curvature scalar. The corresponding characteristic time is typically
much shorter than the cosmological time. | Influence of baryons on spatial distribution of matter: higher order
correlation functions: Baryonic physical processes could leave non-negligible imprint on cosmic
matter distribution pattern. Series of high precision simulation data sets with
identical initial condition are employed for count-in-cell (CIC) analysis,
including one N-body dark matter run, one with adiabatic gas only and one with
dissipative processes. Variances and higher order correlation functions of dark
matter and gas are estimated. It is found that baryon physical processes mainly
affected dark matter distribution at scales less than $1h^{-1}$Mpc. In
comparison with the pure dark matter run, adiabatic process alone strengthens
variance of dark matter by \sim 10% at scale $0.1h^{-1}$Mpc, while $S_n$s of
dark matter deviate from pure dark matter case only mildly at a few
percentages. Dissipative gas run does not differ much to the adiabatic run in
dark matter variance, but renders significantly different $S_n$ parameters of
dark matter, bringing about more than 10% enhancement to $S_3$ at
$0.1h^{-1}$Mpc and $z=0$. Distribution patterns of gas in two hydrodynamical
simulations are prominently different. Variance of gas at $z=0$ decreases by
$\sim 30%$ in adiabatic simulation while by $\sim 60%$ in non-adiabatic
simulation at $0.1h^{-1}$Mpc, the attenuation is weaker at larger scales but
still obvious at $\sim 10h^{-1}$Mpc. $S_n$ parameters of gas are biased upward
at scales $< \sim 4h^{-1}$Mpc, dissipative processes give $\sim 84%$ promotion
at $z=0$ to $S_3$ at $0.1h^{-1}$Mpc against the moderate $\sim 7%$ in adiabatic
simulation. The clustering segregation we observed between gas and dark matter
could have intricate implication on modeling galaxy distribution and relevant
cosmological application demanding fine details of matter distribution in
strongly nonlinear regime. |
GAMA: towards a physical understanding of galaxy formation: The Galaxy And Mass Assembly (GAMA) project is the latest in a tradition of
large galaxy redshift surveys, and is now underway on the 3.9m Anglo-Australian
Telescope at Siding Spring Observatory. GAMA is designed to map extragalactic
structures on scales of 1kpc - 1Mpc in complete detail to a redshift of z~0.2,
and to trace the distribution of luminous galaxies out to z~0.5. The principal
science aim is to test the standard hierarchical structure formation paradigm
of Cold Dark Matter (CDM) on scales of galaxy groups, pairs, discs, bulges and
bars. We will measure (1) the Dark Matter Halo Mass Function (as inferred from
galaxy group velocity dispersions); (2) baryonic processes, such as star
formation and galaxy formation efficiency (as derived from Galaxy Stellar Mass
Functions); and (3) the evolution of galaxy merger rates (via galaxy close
pairs and galaxy asymmetries). Additionally, GAMA will form the central part of
a new galaxy database, which aims to contain 275,000 galaxies with
multi-wavelength coverage from coordinated observations with the latest
international ground- and space-based facilities: GALEX, VST, VISTA, WISE,
HERSCHEL, GMRT and ASKAP. Together, these data will provide increased depth
(over 2 magnitudes), doubled spatial resolution (0.7"), and significantly
extended wavelength coverage (UV through Far-IR to radio) over the main SDSS
spectroscopic survey for five regions, each of around 50 deg^2. This database
will permit detailed investigations of the structural, chemical, and dynamical
properties of all galaxy types, across all environments, and over a 5 billion
year timeline. | Violation of the FRW consistency condition as a signature of
backreaction: We propose a backreaction toy model with realistic features and confront it
with the Union2.1 supernova data. The model provides a good fit even though the
expansion history is quite different from the LCDM model and the effective
equation of state is far from -1. We discuss compatibility (or lack thereof)
with other observations. We show that the FRW consistency condition between
distance and expansion rate is violated with an amplitude that is slightly
below the current observational limits. We expect that this is also the case in
the real universe if backreaction is significant, providing a distinct
signature of backreaction. |
A measurement of the scale of homogeneity in the Early Universe: We present the first measurement of the homogeneity index, $\mathcal{H}$, a
fractal or Hausdorff dimension of the early Universe from the Planck CMB
temperature variations $\delta T$ in the sky. This characterization of the
isotropy scale is model-free and purely geometrical, independent of the
amplitude of $\delta T$. We find evidence of homogeneity ($\mathcal{H}=0$) for
scales larger than $\theta_{\mathcal{H}} = 65.9 \pm 9.2 \deg $ on the CMB sky.
This finding is at odds with the $\Lambda$CDM prediction, which assumes a scale
invariant infinite universe. Such anomaly is consistent with the well known low
quadrupule amplitude in the angular $\delta T$ spectrum, but quantified in a
direct and model independent way. We estimate the significance of our finding
for $\mathcal{H}=0$ using a principal component analysis from the sampling
variations of the observed sky. This analysis is validated with theoretical
prediction of the covariance matrix \textcolor{black}{ and simulations, booth
base purely on data or in the $\Lambda$CDM prediction.} Assuming translation
invariance (and flat geometry) we can convert the isotropy scale
$\theta_\mathcal{H}$ into a (comoving) homogeneity scale which is very close to
the trapped surface generated by the observed cosmological constant $\Lambda$. | Astrophysics from the 21-cm background: This chapter describes the astrophysics encoded by the 21-cm background. We
begin with a brief introduction to the radiative transfer and ionization
chemistry relevant to the high-z intergalactic medium. Then, we will provide a
review of the most plausible sources of ionization and heating in the early
Universe. Finally, we will explore a variety of current 21-cm predictions, and
illustrate the sensitivity of the global 21-cm signal and power spectrum to
parameters of interest. |
Constraints on power law cosmology from cosmic chronometer, standard
ruler, and standard candle data: In this paper I investigate how well simple power law expansion fits
observational data in comparison to the standard $\Lambda$CDM model. I analyze
a data set consisting of cosmic chronometer, standard ruler, and standard
candle measurements, finding that the $\Lambda$CDM model provides a better fit
to most combinations of these data than the power law ansatz. | Constraints on the curvature power spectrum from primordial black hole
evaporation: We estimate the maximum allowed amplitude for the power spectrum of the
primordial curvature perturbations, ${\cal P_R}(k)$, on all scales from the
absence of any detection signals of sub-solar mass black holes. In particular
we analyze the constraints on the PBHs and we focus on the low mass limit where
the Hawking radiation is expected to significantly influence the big bang
observables, considering also different early cosmic histories. We derive the
upper bounds for the variance of density perturbations, $\sigma(M)$, for any
possible reheating temperature as well as for the cosmological scenario of a
scalar condensate domination. We expect our results to have considerable
implications for models designed to generate PBHs, especially in the low mass
range, and provide additional constraints to a large class of inflationary
models. |
Galaxy-galaxy(-galaxy) lensing as a sensitive probe of galaxy evolution: The gravitational lensing effect provides various ways to study the mass
environment of galaxies. We investigate how galaxy-galaxy(-galaxy) lensing can
be used to test models of galaxy formation and evolution. We consider two
semi-analytic galaxy formation models based on the Millennium Run N-body
simulation: the Durham model by Bower et al. (2006) and the Garching model by
Guo et al. (2011). We generate mock lensing observations for the two models,
and then employ Fast Fourier Transform methods to compute second- and
third-order aperture statistics in the simulated fields for various galaxy
samples. We find that both models predict qualitatively similar aperture
signals, but there are large quantitative differences. The Durham model
predicts larger amplitudes in general. In both models, red galaxies exhibit
stronger aperture signals than blue galaxies. Using these aperture measurements
and assuming a linear deterministic bias model, we measure relative bias ratios
of red and blue galaxy samples. We find that a linear deterministic bias is
insufficient to describe the relative clustering of model galaxies below ten
arcmin angular scales. Dividing galaxies into luminosity bins, the aperture
signals decrease with decreasing luminosity for brighter galaxies, but increase
again for fainter galaxies. This increase is likely an artifact due to too many
faint satellite galaxies in massive group and cluster halos predicted by the
models. Our study shows that galaxy-galaxy(-galaxy) lensing is a sensitive
probe of galaxy evolution. | Cosmology with the Highly Redshifted 21cm Line: In addition to being a probe of Cosmic Dawn and Epoch of Reionization
astrophysics, the 21cm line at $z>6$ is also a powerful way to constrain
cosmology. Its power derives from several unique capabilities. First, the 21cm
line is sensitive to energy injections into the intergalactic medium at high
redshifts. It also increases the number of measurable modes compared to
existing cosmological probes by orders of magnitude. Many of these modes are on
smaller scales than are accessible via the CMB, and moreover have the advantage
of being firmly in the linear regime (making them easy to model theoretically).
Finally, the 21cm line provides access to redshifts prior to the formation of
luminous objects. Together, these features of 21cm cosmology at $z>6$ provide
multiple pathways toward precise cosmological constraints. These include the
"marginalizing out" of astrophysical effects, the utilization of redshift space
distortions, the breaking of CMB degeneracies, the identification of signatures
of relative velocities between baryons and dark matter, and the discovery of
unexpected signs of physics beyond the $\Lambda$CDM paradigm at high redshifts. |
Nexus of the Cosmic Web: One of the important unknowns of current cosmology concerns the effects of
the large scale distribution of matter on the formation and evolution of dark
matter haloes and galaxies. One main difficulty in answering this question lies
in the absence of a robust and natural way of identifying the large scale
environments and their characteristics. This work summarizes the NEXUS+
formalism which extends and improves our multiscale scale-space MMF method. The
new algorithm is very successful in tracing the Cosmic Web components, mainly
due to its novel filtering of the density in logarithmic space. The method, due
to its multiscale and hierarchical character, has the advantage of detecting
all the cosmic structures, either prominent or tenuous, without preference for
a certain size or shape. The resulting filamentary and wall networks can easily
be characterized by their direction, thickness, mass density and density
profile. These additional environmental properties allows to us to investigate
not only the effect of environment on haloes, but also how it correlates with
the environment characteristics. | Quantum Discord of Cosmic Inflation: Can we Show that CMB Anisotropies
are of Quantum-Mechanical Origin?: We investigate the quantumness of primordial cosmological fluctuations and
its detectability. The quantum discord of inflationary perturbations is
calculated for an arbitrary splitting of the system, and shown to be very large
on super-Hubble scales. This entails the presence of large quantum
correlations, due to the entangled production of particles with opposite
momentums during inflation. To determine how this is reflected at the
observational level, we study whether quantum correlators can be reproduced by
a non-discordant state, i.e. a state with vanishing discord that contains
classical correlations only. We demonstrate that this can be done for the power
spectrum, the price to pay being twofold: first, large errors in other
two-point correlation functions and second, the presence of intrinsic
non-Gaussianity. The detectability of these two features remains to be
determined but could possibly rule out a non-discordant description of the
cosmic microwave background. If one abandons the idea that perturbations should
be modeled by quantum mechanics and wants to use a classical stochastic
formalism instead, we show that any two-point correlators on super-Hubble
scales can be exactly reproduced regardless of the squeezing of the system. The
latter becomes important only for higher-order correlation functions that can
be accurately reproduced only in the strong squeezing regime. |
JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified
by MACS0416, and implications for dark matter models: We report the discovery of Mothra, an extremely magnified monster star,
likely a binary system of two supergiant stars, in one of the strongly lensed
galaxies behind the galaxy cluster MACS0416. The star is in a galaxy with
spectroscopic redshift $z=2.091$ in a portion of the galaxy that is parsecs
away from the cluster caustic. The binary star is observed only on the side of
the critical curve with negative parity but has been detectable for at least
eight years, implying the presence of a small lensing perturber.
Microlenses alone cannot explain the earlier observations of this object made
with the Hubble Space Telescope. A larger perturber with a mass of at least
$10^4$\,\Msun\ offers a more satisfactory explanation. Based on the lack of
perturbation on other nearby sources in the same arc, the maximum mass of the
perturber is $M< 2.5\times10^6$\,\Msun, making it the smallest substructure
constrained by lensing above redshift 0.3. The existence of this millilens is
fully consistent with the expectations from the standard cold dark matter
model. On the other hand, the existence of such small substructure in a cluster
environment has implications for other dark matter models. In particular, warm
dark matter models with particle masses below 8.7\,keV are excluded by our
observations. Similarly, axion dark matter models are consistent with the
observations only if the axion mass is in the range $0.5\times10^{-22}\, {\rm
eV} < m_a < 5\times10^{-22}\, {\rm eV}$. | ANNz2 - photometric redshift and probability distribution function
estimation using machine learning: We present ANNz2, a new implementation of the public software for photometric
redshift (photo-z) estimation of Collister and Lahav (2004), which now includes
generation of full probability distribution functions (PDFs). ANNz2 utilizes
multiple machine learning methods, such as artificial neural networks and
boosted decision/regression trees. The objective of the algorithm is to
optimize the performance of the photo-z estimation, to properly derive the
associated uncertainties, and to produce both single-value solutions and PDFs.
In addition, estimators are made available, which mitigate possible problems of
non-representative or incomplete spectroscopic training samples. ANNz2 has
already been used as part of the first weak lensing analysis of the Dark Energy
Survey, and is included in the experiment's first public data release. Here we
illustrate the functionality of the code using data from the tenth data release
of the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic
Survey. The code is available for download at
https://github.com/IftachSadeh/ANNZ . |
Correcting correlation functions for redshift-dependent interloper
contamination: The construction of catalogues of a particular type of galaxy can be
complicated by interlopers contaminating the sample. In spectroscopic galaxy
surveys this can be due to the misclassification of an emission line; for
example in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) low
redshift [OII] emitters may make up a few percent of the observed Ly${\alpha}$
emitter (LAE) sample. The presence of contaminants affects the measured
correlation functions and power spectra. Previous attempts to deal with this
using the cross-correlation function have assumed sources at a fixed redshift,
or not modelled evolution within the adopted redshift bins. However, in
spectroscopic surveys like HETDEX, where the contamination fraction is likely
to be redshift dependent, the observed clustering of misclassified sources will
appear to evolve strongly due to projection effects, even if their true
clustering does not. We present a practical method for accounting for the
presence of contaminants with redshift-dependent contamination fractions and
projected clustering. We show using mock catalogues that our method, unlike
existing approaches, yields unbiased clustering measurements from the upcoming
HETDEX survey in scenarios with redshift-dependent contamination fractions
within the redshift bins used. We show our method returns auto-correlation
functions with systematic biases much smaller than the statistical noise for
samples with at least as high as 7 per cent contamination. We also present and
test a method for fitting for the redshift-dependent interloper fraction using
the LAE-[OII] galaxy cross-correlation function, which gives less biased
results than assuming a single interloper fraction for the whole sample. | The Hubble Tension in Light of the Full-Shape Analysis of Large-Scale
Structure Data: The disagreement between direct late-time measurements of the Hubble constant
from the SH0ES collaboration, and early-universe measurements based on the
$\Lambda$CDM model from the Planck collaboration might, at least in principle,
be explained by new physics in the early universe. Recently, the application of
the Effective Field Theory of Large-Scale Structure to the full shape of the
power spectrum of the SDSS/BOSS data has revealed a new, rather powerful, way
to measure the Hubble constant and the other cosmological parameters from
Large-Scale Structure surveys. In light of this, we analyze two models for
early universe physics, Early Dark Energy and Rock 'n' Roll, that were designed
to significantly ameliorate the Hubble tension. Upon including the information
from the full shape to the Planck, BAO, and Supernovae measurements, we find
that the degeneracies in the cosmological parameters that were introduced by
these models are well broken by the data, so that these two models do not
significantly ameliorate the tension. |
Probing new physics with multi-vacua quantum tunnelings beyond standard
model through gravitational waves: We report on a novel phenomenon of particle cosmology, which features
specific cosmological phase transitions via quantum tunnelings through multiple
vacua. The latter is inspired by the axiverse ideas and enables us to probe the
associated new physics models through a potential observation of specific
patterns in the stochastic gravitational waves background. Multiple vacua may
induce the nucleation of co-existing bubbles over the phase transition epoch,
hence enhancing the overall process of bubbles' nucleation. Our detailed
analysis of semi-analytical and numerical solutions to the bounce equations of
the path integral in three vacua case has enabled us to determine the existence
of three instanton solutions. This new mechanism of cosmological phase
transitions clearly predicts a possibly sizeable new source of gravitational
waves, with its energy spectrum being featured with particular patterns, which
could be probed by the future gravitational wave interferometers. | Accretion, Growth of Supermassive Black Holes, and Feedback in Galaxy
Mergers: Super-Eddington accretion is very efficient in growing the mass of a black
hole: in a fraction of the Eddington time its mass can grow to an arbitrary
large value if the feedback effect is not taken into account. However, since
super-Eddington accretion has a very low radiation efficiency, people have
argued against it as a major process for the growth of the black holes in
quasars since observations have constrained the average accretion efficiency of
the black holes in quasars to be $\ga 0.1$. In this paper we show that the
observational constraint does not need to be violated if the black holes in
quasars have undergone a two-phase growing process: with a short
super-Eddington accretion process they get their masses inflated by a very
large factor until the feedback process becomes important, then with a
prolonged sub-Eddington accretion process they have their masses increased by a
factor $\ga 2$. The overall average efficiency of this two-phase process is
then $\ga 0.1$, and the existence of black holes of $10^9 M_\odot$ by redshift
6 is easily explained. Observational test of the existence of the
super-Eddington accretion phase is briefly discussed. |
Recoiling Black Holes in Merging Galaxies: Relationship to AGN
Lifetimes, Starbursts, and the M-sigma Relation: Gravitational-wave (GW) recoil of merging supermassive black holes (SMBHs)
may influence the co-evolution of SMBHs and their host galaxies. We examine
this possibility using SPH/N-body simulations of gaseous galaxy mergers in
which the merged BH receives a recoil kick. This enables us to follow recoiling
BHs in self-consistent, evolving merger remnants. In contrast to recent studies
on similar topics, we conduct a large parameter study, generating a suite of
over 200 simulations with more than 60 merger models and a range of recoil
velocities (vk). Our main results are as follows. (1) BHs kicked at nearly the
central escape speed (vesc) may oscillate on large orbits for up to a Hubble
time, but in gas-rich mergers, BHs kicked with up to ~ 0.7 vesc may be confined
to the central few kpc of the galaxy, owing to gas drag and steep central
potentials. (2) vesc in gas-rich mergers may increase rapidly during final
coalescence, in which case trajectories may depend on the timing of the BH
merger relative to the formation of the potential well. (3) Recoil events
generally reduce the lifetimes of bright active galactic nuclei (AGN), but may
actually extend AGN lifetimes at lower luminosities. (4) Kinematically-offset
AGN (v > 800 km s^-1) may be observable for up to ~ 10 Myr either immediately
after the recoil or during pericentric passages through a gas-rich remnant. (5)
Spatially-offset AGN (R > 1 kpc) generally have low luminosities and lifetimes
of ~ 1 - 100 Myr. (6) Rapidly-recoiling BHs may be up to ~ 5 times less massive
than their stationary counterparts. This lowers the normalization of the
M-sigma relation and contributes to both intrinsic and overall scatter. (7)
Finally, the displacement of AGN feedback after a recoil event enhances central
star formation rates, thereby extending the starburst phase of the merger and
creating a denser stellar cusp. [Abridged.] | The FLAMINGO project: the coupling between baryonic feedback and
cosmology in light of the $S_8$ tension: Large-scale structure surveys have reported measurements of the density of
matter, $\Omega_\mathrm{m}$, and the amplitude of clustering, $\sigma_8$, that
are in tension with the values inferred from observations of the cosmic
microwave background. While this may be a sign of new physics that slows the
growth of structure at late times, strong astrophysical feedback processes
could also be responsible. In this work, we argue that astrophysical processes
are not independent of cosmology and that their coupling naturally leads to
stronger baryonic feedback in cosmological models with suppressed structure
formation or when combined with a mechanism that removes dark matter from
halos. We illustrate this with two well-motivated extensions of the Standard
Model known to suppress structure formation: massive neutrinos and decaying
dark matter. Our results, based on the FLAMINGO suite of hydrodynamical
simulations, show that the combined effect of baryonic and non-baryonic
suppression mechanisms is greater than the sum of its parts, particularly for
decaying dark matter. We also show that the dependence of baryonic feedback on
cosmology can be modelled as a function of the ratio
$f_\mathrm{b}/c^2_\mathrm{v}\sim
f_\mathrm{b}/(\Omega_\mathrm{m}\sigma_8)^{1/4}$ of the universal baryon
fraction, $f_\mathrm{b}$, to a velocity-based definition of halo concentration,
$c^2_\mathrm{v}$, giving an accurate fitting formula for the baryonic
suppression of the matter power spectrum. Although the combination of baryonic
and non-baryonic suppression mechanisms can resolve the tension, the models
with neutrinos and decaying dark matter are challenged by constraints on the
expansion history. |
A review of the discovery reach of directional Dark Matter detection: Cosmological observations indicate that most of the matter in the Universe is
Dark Matter. Dark Matter in the form of Weakly Interacting Massive Particles
(WIMPs) can be detected directly, via its elastic scattering off target nuclei.
Most current direct detection experiments only measure the energy of the
recoiling nuclei. However, directional detection experiments are sensitive to
the direction of the nuclear recoil as well. Due to the Sun's motion with
respect to the Galactic rest frame, the directional recoil rate has a dipole
feature, peaking around the direction of the Solar motion. This provides a
powerful tool for demonstrating the Galactic origin of nuclear recoils and
hence unambiguously detecting Dark Matter. Furthermore, the directional recoil
distribution depends on the WIMP mass, scattering cross section and local
velocity distribution. Therefore, with a large number of recoil events it will
be possible to study the physics of Dark Matter in terms of particle and
astrophysical properties. We review the potential of directional detectors for
detecting and characterizing WIMPs. | A Framework for Measuring Weak-Lensing Magnification Using the
Fundamental Plane: Galaxy-galaxy lensing is an essential tool for probing dark matter halos and
constraining cosmological parameters. While galaxy-galaxy lensing measurements
usually rely on shear, weak-lensing magnification contains additional
constraining information. Using the fundamental plane (FP) of elliptical
galaxies to anchor the size distribution of a background population is one
method that has been proposed for performing a magnification measurement. We
present a formalism for using the FP residuals of elliptical galaxies to
jointly estimate the foreground mass and background redshift errors for a
stacked lens scenario. The FP residuals include information about weak-lensing
magnification $\kappa$, and therefore foreground mass, since to first order,
nonzero $\kappa$ affects galaxy size but not other FP properties. We also
present a modular, extensible code that implements the formalism using emulated
galaxy catalogs of a photometric galaxy survey. We find that combining FP
information with observed number counts of the source galaxies constrains mass
and photo-z error parameters significantly better than an estimator that
includes number counts only. In particular, the constraint on the mass is
17.0\% if FP residuals are included, as opposed to 27.7\% when only number
counts are included. The effective size noise for a foreground lens of mass
$M_H=10^{14}M_\odot$, with a conservative selection function in size and
surface brightness applied to the source population, is
$\sigma_{\kappa,\mathrm{eff}}=0.250$. We discuss the improvements to our FP
model necessary to make this formalism a practical companion to shear analyses
in weak lensing surveys. |
The Star Formation Histories of Red-Sequence Galaxies, Mass-to-Light
Ratios and the Fundamental Plane: This paper addresses the challenge of understanding the typical star
formation histories of red sequence galaxies, using linestrength indices and
mass-to-light ratios as complementary constraints on their stellar age
distribution. We construct simple parametric models of the star formation
history that bracket a range of scenarios, and fit these models to the
linestrength indices of low-redshift cluster red-sequence galaxies. For giant
galaxies, we confirm the downsizing trend. We find, however, that this trend
flattens or reverses at sigma < 70 km/s. We then compare predicted stellar
mass-to-light ratios with dynamical mass-to-light ratios derived from the
Fundamental Plane (FP), or by the SAURON group. For galaxies with sigma ~ 70
km/s, models with a "frosting" of young stars and models with exponential star
formation histories have stellar mass-to-light ratios that are larger than
observed dynamical mass-to-light ratios by factors of 1.7 and 1.4,
respectively, and so are rejected. The SSP model is consistent with the FP, and
requires a modest amount of dark matter (20-30%) to account for the difference
between stellar and dynamical mass-to-light ratios. A model in which star
formation was "quenched" at intermediate ages is also consistent with the
observations. We find that the contribution of stellar populations to the
"tilt" of the FP is highly dependent on the assumed star-formation history: for
the SSP model, the tilt of the FP is driven primarily by stellar-population
effects. For a quenched model, two-thirds of the tilt is due to stellar
populations and only one third is due to dark matter or non-homology. | VLBI observations of Brightest Cluster Galaxies: are cooling and parsec
scale morphology correlated?: We present a statistical study on parsec scale properties of a sample of
Brigthest Cluster Galaxies (BCGs) in Abell Clusters. These data show a possible
difference between BCGs in cool core clusters (two-sided parsec scale jets) and
in non cool core clusters (one-sided parsec scale jet). We suggest that the
two-sided morphology in cool core clusters could be due to the presence of
mildly relativistic jets slowed down already at mas scale as consequence of the
jet interaction with a dense surrounding medium. |
Active and Sterile Neutrino Emission and SN1987A Pulsar Velocity: Recently estimates have been made of the velocities of pulsars produced by
the emission of sterile neutrinos during the first 10 seconds and by active
neutrinos during the second 10 seconds after a supernova event reaches thermal
equilibrium. Neutrinos produced with electrons in the lowest Landau level are
emitted in the direction of the magnetic field, and the resulting pulsar
velocity depends mainly on the temperature. Using measurements of the neutrino
energies emitted from SN1987A, the temperature can be estimated, and from this
we estimate the velocity of the resulting pulsar from both active and large
mixing-angle sterile neutrinos. | Cosmological perturbations in f(T) gravity: We investigate the cosmological perturbations in f(T) gravity. Examining the
pure gravitational perturbations in the scalar sector using a diagonal
vierbien, we extract the corresponding dispersion relation, which provides a
constraint on the f(T) ansatzes that lead to a theory free of instabilities.
Additionally, upon inclusion of the matter perturbations, we derive the fully
perturbed equations of motion, and we study the growth of matter overdensities.
We show that f(T) gravity with f(T) constant coincides with General Relativity,
both at the background as well as at the first-order perturbation level.
Applying our formalism to the power-law model we find that on large subhorizon
scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ
from LCDM cosmology. Finally, examining the linear perturbations of the vector
and tensor sectors, we find that (for the standard choice of vierbein) f(T)
gravity is free of massive gravitons. |
Empirical Delay Time Distributions of Type Ia Supernovae From The
Extended GOODS/HST Supernova Survey: Using the Hubble Space Telescope ACS imaging of the GOODS North and South
fields during Cycles 11, 12, and 13, we derive empirical constraints on the
delay-time distribution function for type Ia supernovae. We extend our previous
analysis to the three-year sample of 56 SNe Ia over the range 0.2<z<1.8, using
a Markov chain Monte Carlo to determine the best-fit unimodal delay-time
distribution function. The test, which ultimately compares the star formation
rate density history to the unbinned volumetric SN Ia rate history from the
GOODS/HST-SN survey, reveals a SN Ia delay-time distribution that is tightly
confined to 3-4 Gyrs (to >95% confidence). This result is difficult to resolve
with any intrinsic delay-time distribution function (bimodal or otherwise), in
which a substantial fraction (e.g., >10%) of events are ``prompt'', requiring
less than approximately 1 Gyr to develop from formation to explosion. The
result is, however, strongly motivated by the decline in the number of SNe Ia
at z>1.2. Sub-samples of the HST-SN data confined to lower redshifts (z<1) show
plausible delay-time distributions that are dominated by prompt events, which
is more consistent with results from low-redshift supernova samples and
supernova host galaxy properties. Scenarios in which a substantial fraction of
z>1.2 supernovae are extraordinarily obscured by dust may partly explain the
differences in low-z and high-z results. Other possible resolutions may include
environmental dependencies (such as gas-phase metallicity) that affect the
progenitor mechanism efficiency, especially in the early universe. | Bayesian Analysis of Inflation III: Slow Roll Reconstruction Using Model
Selection: We implement Slow Roll Reconstruction -- an optimal solution to the inverse
problem for inflationary cosmology -- within ModeCode, a publicly available
solver for the inflationary dynamics. We obtain up-to-date constraints on the
reconstructed inflationary potential, derived from the WMAP 7-year dataset and
South Pole Telescope observations, combined with large scale structure data
derived from SDSS Data Release 7. Using ModeCode in conjunction with the
MultiNest sampler, we compute Bayesian evidence for the reconstructed potential
at each order in the truncated slow roll hierarchy. We find that the data are
well-described by the first two slow roll parameters, \epsilon and \eta, and
that there is no need to include a nontrivial \xi parameter. |
Integral field spectroscopy in the near infrared of NGC 3125-A and SBS
0335-052: We present integral field spectroscopy in the near infrared of the nearby
dwarf starburst galaxies NGC 3125-A and of the low metallicity dwarf galaxy SBS
0335-052. The use of adaptive optics in the observations produces sub-arcsecond
angular resolution. We pinpoint the star forming cores of both galaxies,
identify relevant ISM components such as dust, photo ionized gas, shock excited
gas and molecular gas. We relate these components to the large scale star
formation process of the galaxies. In particular we find the emission of the
near infrared lines of H2 and especially [FeII] does not coincide with the HII
region in NGC 3125. We have the first clear detection of [FeII] in SBS
0335-052. | Red, Straight, no bends: primordial power spectrum reconstruction from
CMB and large-scale structure: We present a minimally parametric, model independent reconstruction of the
shape of the primordial power spectrum. Our smoothing spline technique is
well-suited to search for smooth features such as deviations from scale
invariance, and deviations from a power law such as running of the spectral
index or small-scale power suppression. We use a comprehensive set of the
state-of the art cosmological data: {\it Planck} observations of the
temperature and polarisation anisotropies of the cosmic microwave background,
WiggleZ and Sloan Digital Sky Survey Data Release 7 galaxy power spectra and
the Canada-France-Hawaii Lensing Survey correlation function. This
reconstruction strongly supports the evidence for a power law primordial power
spectrum with a red tilt and disfavours deviations from a power law power
spectrum including small-scale power suppression such as that induced by
significantly massive neutrinos. This offers a powerful confirmation of the
inflationary paradigm, justifying the adoption of the inflationary prior in
cosmological analyses. |
ALFALFA HI Data Stacking III. Comparison of environmental trends in HI
gas mass fraction and specific star formation rate: It is well known that both the star formation rate and the cold gas content
of a galaxy depend on the local density out to distances of a few Megaparsecs.
In this paper, we compare the environmental density dependence of the atomic
gas mass fractions of nearby galaxies with the density dependence of their
central and global specific star formation rates. We stack HI line spectra
extracted from the Arecibo Legacy Fast ALFA survey centered on galaxies with UV
imaging from GALEX and optical imaging/spectroscopy from SDSS. We use these
stacked spectra to evaluate the mean atomic gas mass fraction of galaxies in
bins of stellar mass and local density. For galaxies with stellar masses less
than 10^10.5 M_sun, the decline in mean atomic gas mass fraction with density
is stronger than the decline in mean global and central specific star formation
rate. The same conclusion does not hold for more massive galaxies. We interpret
our results as evidence for ram-pressure stripping of atomic gas from the outer
disks of low mass satellite galaxies. We compare our results with the
semi-analytic recipes of Guo et al. (2011) implemented on the Millennium II
simulation. These models assume that only the diffuse gas surrounding satellite
galaxies is stripped, a process that is often termed "strangulation". We show
that these models predict relative trends in atomic gas and star formation that
are in disagreement with observations. We use mock catalogues generated from
the simulation to predict the halo masses of the HI-deficient galaxies in our
sample. We conclude that ram-pressure stripping is likely to become effective
in dark matter halos with masses greater than 10^13 M_sun. | Macro Dark Matter: Dark matter is a vital component of the current best model of our universe,
$\Lambda$CDM. There are leading candidates for what the dark matter could be
(e.g. weakly-interacting massive particles, or axions), but no compelling
observational or experimental evidence exists to support these particular
candidates, nor any beyond-the-Standard-Model physics that might produce such
candidates. This suggests that other dark matter candidates, including ones
that might arise in the Standard Model, should receive increased attention.
Here we consider a general class of dark matter candidates with characteristic
masses and interaction cross-sections characterized in units of grams and
cm$^2$, respectively -- we therefore dub these macroscopic objects as Macros.
Such dark matter candidates could potentially be assembled out of Standard
Model particles (quarks and leptons) in the early universe. A combination of
Earth-based, astrophysical, and cosmological observations constrain a portion
of the Macro parameter space. A large region of parameter space remains, most
notably for nuclear-dense objects with masses in the range $55 - 10^{17}$ g and
$2\times10^{20} - 4\times10^{24}$ g, although the lower mass window is closed
for Macros that destabilize ordinary matter. |
The Impact of the WHIM on the IGM Thermal State Determined from the
Low-$z$ Lyman-$α$ Forest: At $z \lesssim 1$, shock heating caused by large-scale velocity flows and
possibly violent feedback from galaxy formation, converts a significant
fraction of the cool gas ($T\sim 10^4$ K) in the intergalactic medium (IGM)
into warm-hot phase (WHIM) with $T >10^5$K, resulting in a significant
deviation from the previously tight power-law IGM temperature-density
relationship, $T=T_0 (\rho / {\bar{\rho}})^{\gamma -1}$. This study explores
the impact of the WHIM on measurements of the low-$z$ IGM thermal state,
$[T_0,\gamma]$, based on the $b$-$N_{H I}$ distribution of the Lyman-$\alpha$
forest. Exploiting a machine learning-enabled simulation-based inference method
trained on Nyx hydrodynamical simulations, we demonstrate that [$T_0$,
$\gamma$] can still be reliably measured from the $b$-$N_{H I}$ distribution at
$z=0.1$, notwithstanding the substantial WHIM in the IGM. To investigate the
effects of different feedback, we apply this inference methodology to mock
spectra derived from the IllustrisTNG and Illustris simulations at $z=0.1$. The
results suggest that the underlying $[T_0,\gamma]$ of both simulations can be
recovered with biases as low as $|\Delta \log(T_0/\text{K})| \lesssim 0.05$
dex, $|\Delta \gamma | \lesssim 0.1$, smaller than the precision of a typical
measurement. Given the large differences in the volume-weighted WHIM fractions
between the three simulations (Illustris 38\%, IllustrisTNG 10\%, Nyx 4\%) we
conclude that the $b$-$N_{H I}$ distribution is not sensitive to the WHIM under
realistic conditions. Finally, we investigate the physical properties of the
detectable Lyman-$\alpha$ absorbers, and discover that although their $T$ and
$\Delta$ distributions remain mostly unaffected by feedback, they are
correlated with the photoionization rate used in the simulation. | Constraints on extended Bekenstein models from cosmological,
astrophysical, and local data: Searching for variations of nature's fundamental constants is a crucial step
in our quest to go beyond our current standard model of fundamental physics. If
they exist, such variations will be very likely driven by the existence of a
new fundamental field. The Bekenstein model and its extensions introduce such a
scalar field in a purely phenomenological way, inducing a variation of the
fine-structure constant on cosmological scales. This theoretical framework is
as simple and general as possible while still preserving all the symmetries of
standard quantum electrodynamics. When allowing for couplings to the other
sectors of the Universe, such as baryons, dark matter, and the cosmological
constant, the Bekenstein model is expected to reproduce the low energy limits
of several grand unification, quantum gravity, and higher dimensional theories.
In this work, we constrain different versions of the Bekenstein model by
confronting the full cosmological evolution of the field with an extensive set
of astrophysical, cosmological, and local measurements. We show that couplings
of the order of parts per million (ppm) are excluded for all the cases
considered, imposing strong restrictions on theoretical frameworks aiming to
deal with variations of the fine-structure constant. |
Galaxy Bias and its Effects on the Baryon Acoustic Oscillations
Measurements: The baryon acoustic oscillation (BAO) feature in the clustering of matter in
the universe serves as a robust standard ruler and hence can be used to map the
expansion history of the universe. We use high force resolution simulations to
analyze the effects of galaxy bias on the measurements of the BAO signal. We
apply a variety of Halo Occupation Distributions (HODs) and produce biased mass
tracers to mimic different galaxy populations. We investigate whether galaxy
bias changes the non-linear shifts on the acoustic scale relative to the
underlying dark matter distribution presented by Seo et al (2009). For the less
biased HOD models (b < 3), we do not detect any shift in the acoustic scale
relative to the no-bias case, typically 0.10% \pm 0.10%. However, the most
biased HOD models (b > 3) show a shift at moderate significance (0.79% \pm
0.31% for the most extreme case). We test the one-step reconstruction technique
introduced by Eisenstein et al. (2007) in the case of realistic galaxy bias and
shot noise. The reconstruction scheme increases the correlation between the
initial and final (z = 1) density fields achieving an equivalent level of
correlation at nearly twice the wavenumber after reconstruction. Reconstruction
reduces the shifts and errors on the shifts. We find that after reconstruction
the shifts from the galaxy cases and the dark matter case are consistent with
each other and with no shift. The 1-sigma systematic errors on the distance
measurements inferred from our BAO measurements with various HODs after
reconstruction are about 0.07% - 0.15%. | Imprints of Massive Primordial Fields on Large-Scale Structure: Attention has focussed recently on models of inflation that involve a second
or more fields with a mass near the inflationary Hubble parameter $H$, as may
occur in supersymmetric theories if the supersymmetry-breaking scale is not far
from $H$. Quasi-single-field (QsF) inflation is a relatively simple family of
phenomenological models that serve as a proxy for theories with additional
fields with masses $m\sim H$. Since QsF inflation involves fields in addition
to the inflaton, the consistency conditions (ccs) between correlations that
arise in single-clock inflation are not necessarily satisfied. As a result,
correlation functions in the squeezed limit may be larger than in single-field
inflation. Scalar non-Gaussianities mediated by the massive isocurvature field
in QsF have been shown to be potentially observable. These are especially
interesting since they would convey information about the mass of the
isocurvature field. Here we consider non-Gaussian correlators involving tensor
modes and their observational signatures. A physical correlation between a
(long-wavelength) tensor mode and two scalar modes (tss), for instance, may
give rise to local departures from statistical isotropy or, in other words, a
non-trivial four-point function. The presence of the tensor mode may moreover
be inferred geometrically from the shape dependence of the four-point function.
We compute tss and stt (one soft curvature mode and two hard tensors) bispectra
in QsF inflation, identifying the conditions necessary for these to "violate"
the ccs. We find that while ccs are violated by stt correlations, they are
preserved by the tss in the minimal QsF model. Our study of primordial
correlators which include gravitons in seeking imprints of additional fields
with masses $m\sim H$ during inflation can be seen as complementary to the
recent "cosmological collider physics" proposal. |
Planck 2013 results. XIV. Zodiacal emission: The Planck satellite provides a set of all-sky maps at nine frequencies from
30 GHz to 857 GHz. Planets, minor bodies, and diffuse interplanetary dust
emission (IPD) are all observed. The IPD can be separated from Galactic and
other emissions because Planck views a given point on the celestial sphere
multiple times, through different columns of IPD. We use the Planck data to
investigate the behaviour of zodiacal emission over the whole sky at
sub-millimetre and millimetre wavelengths. We fit the Planck data to find the
emissivities of the various components of the COBE zodiacal model -- a diffuse
cloud, three asteroidal dust bands, a circumsolar ring, and an Earth-trailing
feature. The emissivity of the diffuse cloud decreases with increasing
wavelength, as expected from earlier analyses. The emissivities of the dust
bands, however, decrease less rapidly, indicating that the properties of the
grains in the bands are different from those in the diffuse cloud. We fit the
small amount of Galactic emission seen through the telescope's far sidelobes,
and place limits on possible contamination of the CMB results from both
zodiacal and far-sidelobe emission. When necessary, the results are used in the
Planck pipeline to make maps with zodiacal emission and far sidelobes removed.
We show that the zodiacal correction to the CMB maps is small compared to the
Planck CMB temperature power spectrum and give a list of flux densities for
small Solar System bodies. | Mass reconstruction by gravitational shear and flexion: Galaxy clusters are considered as excellent probes for cosmology. For that
purpose, their mass needs to be measured and their structural properties needs
to be understood. We propose a method for galaxy cluster mass reconstruction
which combines information from strong lensing, weak lensing shear and flexion.
We extend the weak lensing analysis to the inner parts of the cluster and, in
particular, improve the resolution of substructure. We use simulations to show
that the method recovers the mass density profiles of the cluster. We find that
the weak lensing flexion is sensitive to substructure. After combining the
flexion data into the joint weak and strong lensing analysis, we can resolve
the cluster properties with substructures. |
A quantitative criteria for the coincidence problem: The cosmic coincidence problem is a serious challenge to dark energy model.
We suggest a quantitative criteria for judging the severity of the coincidence
problem. Applying this criteria to three different interacting models,
including the interacting quintessence, interacting phantom, and interacting
Chaplygin gas models, we find that the interacting Chaplygin gas model has a
better chance to solve the coincidence problem. Quantitatively, we find that
the coincidence index C for the interacting Chaplygin gas model is smaller than
that for the interacting quintessence and phantom models by six orders of
magnitude. | The extent of gravitationally bound structure in a ΛCDM universe: A new analytical model for constraining the extent of gravitationally bound
structure in the Universe is presented. This model is based on a simple
modification of the spherical collapse model (SCM), and its performance in
predicting the limits of bound structure in N-body simulations is compared to
that of two previous models with the aid of new software named COLDGaS--
compute unified device architecture (CUDA) object location determination in
GADGET2 snapshots -- which was developed by the author. All of these models can
be distilled down to a single unique parameter {\xi}, here named the critical
parameter, which was found to have values of 3 and 1.18 from the previous
studies, and a value of 1.89 from the modified SCM. While still on the
conservative side, this new model tends to better identify what structure is
gravitationally bound in simulations. All three analytical models are applied
to the Corona Borealis supercluster, with the modified SCM and {\xi} = 1.18
model making predictions that are in agreement with recent work showing that
A2056, A2061, A2065, A2067, and A2089 comprise a gravitationally bound
supercluster. As an additional test, the modified SCM is used to estimate the
mass within the turn around radius of the Virgo cluster, providing results in
good agreement with studies relating the virial mass of clusters to the total
mass within turn around. |
Spectral-based k-corrections and implications for the colour-magnitude
relation of E/S0s and its evolution: We select a sample of 70378 E/S0 (early-type) galaxies at 0<z<0.36 from the
Sloan Digital Sky Survey, excluding disk and star-forming galaxies. We estimate
g and r magnitudes in the observer- and rest-frames directly from the SDSS DR6
spectra; this provides an object-by-object estimate of the k-correction. We use
the k-corrections from the spectra to study the evolution of the rest-frame
colour-magnitude relation (CMR) and colour-sigma (velocity dispersion) relation
(CsigmaR). The evolution is very sensitive to the k-correction. Both the CMR
and CsigmaR evolve blueward with increasing redshift, approximately in
agreement with passive evolution models with age approx. 12 Gyr. The slope and
zero-point of the CMR depend on whether colours were defined in fixed physical
or angular apertures, a consequence of the fact that the centers of these
objects tend to be redder: the relation is steeper for fixed angular apertures.
One the other hand, the CsigmaR slope does not show this dependence on the
aperture in which the colour was defined, suggesting that colour gradients are
correlated with residuals from the sigma-M_r relation. As these residuals are
age indicators, our findings suggest that colour gradients correlate with the
age of the stellar population. | Multiwavelength studies of hard X-ray selected sources: Hard X-ray surveys like those provided by IBIS and BAT on board the INTEGRAL
and Swift satellites list a significant number of sources which are
unidentified and/or unclassified and which deserve multiwaveband observations
to be properly characterized. In this work we have been able to follow up 148
such sources, finding 27 X-ray binaries and 121 Active Galactic Nuclei (AGN).
From the AGN sample we extracted a set of 94 AGN, belonging to the
INTEGRAL/IBIS and Swift/BAT surveys, for which we performed an X-ray study to
determine absorption and 2-10 keV flux by means of XMM-Newton and Swift/XRT
available observations. Using a new diagnostic diagram we identified a few
peculiar sources which apparently do not fit within the AGN unified theory.
Finally, we have compared the optical versus X-ray properties of these 94 AGN
to study the optical reddening versus the X-ray absorption local to the AGN |
How to distinguish starbursts and quiescently star-forming galaxies: The
`bimodal' submillimetre galaxy population as a case study: In recent work (arXiv:1101.0002) we have suggested that the high-redshift (z
~ 2-4) bright submillimetre galaxy (SMG) population is heterogeneous, with
major mergers contributing both at early stages, where quiescently star-forming
discs are blended into one submm source (`galaxy-pair SMGs'), and late stages,
where mutual tidal torques drive gas inflows and cause strong starbursts. Here
we combine hydrodynamic simulations of major mergers with 3-D dust radiative
transfer calculations to determine observational diagnostics that can
distinguish between quiescently star-forming SMGs and starburst SMGs via
integrated data alone. We fit the far-IR SEDs of the simulated galaxies with
the optically thin single-temperature modified blackbody, the full form of the
single-temperature modified blackbody, and a power-law temperature-distribution
model. The effective dust temperature, T_dust, and power-law index of the dust
emissivity in the far-IR, \beta, derived can significantly depend on the
fitting form used, and the intrinsic \beta\ of the dust is not recovered.
However, for all forms used here, there is a T_dust above which almost all
simulated galaxies are starbursts, so a T_dust cut is very effective at
selecting starbursts. Simulated merger-induced starbursts also have higher
L_IR/M_gas and L_IR/L_FUV than quiescently star-forming galaxies and lie above
the star formation rate-stellar mass relation. These diagnostics can be used to
test our claim that the SMG population is heterogeneous and to observationally
determine what star formation mode dominates a given galaxy population. We
comment on applicability of these diagnostics to ULIRGs that would not be
selected as SMGs. These `hot-dust ULIRGs' are typically starburst galaxies
lower in mass than SMGs, but they can also simply be SMGs observed from a
different viewing angle. | A Lagrangian Perturbation Theory in the presence of massive neutrinos: We develop a Lagrangian Perturbation Theory (LPT) framework to study the
clustering of cold dark matter (CDM) in cosmologies with massive neutrinos. We
follow the trajectories of CDM particles with Lagrangian displacements fields
up to third order in perturbation theory. Once the neutrinos become
non-relativistic, their density fluctuations are modeled as being proportional
to the CDM density fluctuations, with a scale-dependent proportionality factor.
This yields a gravitational back-reaction that introduces additional scales to
the linear growth function, which is accounted for in the higher order LPT
kernels. Through non-linear mappings from Eulerian to Lagrangian frames, we
ensure that our theory has a well behaved large scale behavior free of unwanted
UV divergences, which are common when neutrino and CDM densities are not
treated on an equal footing, and in resummation schemes that manifestly break
Galilean invariance. We use our theory to construct correlation functions for
both the underlying matter field, as well as for biased tracers using
Convolution-LPT. Redshift-space distortions effects are modeled using the
Gaussian Streaming Model. When comparing our analytical results to simulated
data from the Quijote simulation suite, we find good accuracy down to $r=20
\,\text{Mpc} \, h^{-1}$ at redshift $z=0.5$, for the real space and redshift
space monopole particle correlation functions with no free parameters. The same
accuracy is reached for the redshift space quadrupole if we additionally
consider an effective field theory parameter that shifts the pairwise velocity
dispersion. For modeling the correlation functions of tracers we adopt a simple
Lagrangian biasing scheme with only density and curvature operators, which we
find sufficient to reach down to $r=20 \,\text{Mpc} \, h^{-1}$ when comparing
to simulated halos. |
Taylor expansion of luminosity distance in Szekeres cosmological models:
Effects of local structures evolution on cosmographic parameters: We consider the Goode-Wainwright representation of the Szekeres cosmological
models and calculate the Taylor expansion of the luminosity distance in order
to study the effects of the inhomogeneities on cosmographic parameters. Without
making a particular choice for the arbitrary functions defining the metric, we
Taylor expand up to the second order in redshift for Family I and up to the
third order for Family II Szekeres metrics under the hypotesis, based on
observation, that local structure formation is over. In a conservative fashion,
we also allow for the existence of a non null cosmological constant. | Dipolar Dark Matter and Cosmology: The phenomenology of the modified Newtonian dynamics (MOND) can be recovered
from a mechanism of "gravitational polarization" of some dipolar medium playing
the role of dark matter. We review a relativistic model of dipolar dark matter
(DDM) within standard general relativity to describe, at some effective level,
a fluid polarizable in a gravitational field. At first order in cosmological
perturbation theory, this model is equivalent to the concordance cosmological
scenario, or Lambda-cold dark matter (CDM) model. At second order, however, the
internal energy of DDM modifies the curvature perturbation generated by CDM.
This correction, which depends quadratically on the dipole, induces a new type
of non-Gaussianity in the bispectrum of the curvature perturbation with respect
to standard CDM. Recent observations by the Planck satellite impose stringent
constraints on the primordial value of the dipole field. |
Challenges to our understanding of radio relics: X-ray observations of
the Toothbrush cluster: The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three
radio relics and a giant radio halo. The northern relic, the Toothbrush, is
1.9-Mpc long and has an unusual linear morphology. According to simple
diffusive shock acceleration theory, its radio spectral index indicates a Mach
number of 3.3-4.6. Here, we present results from a deep XMM-Newton observation
of the cluster. We observe two distinct cluster cores that have survived the
merger. The presence of three shocks at or near the locations of the radio
relics is confirmed by density and temperature discontinuities. However, the
observation poses several puzzles that challenge our understanding of radio
relics: (i) at the Toothbrush, the shock Mach number is not larger than 2, in
apparent conflict with the shock strength predicted from the radio spectrum;
(ii) at the Toothbrush, the shock front is, in part, spatially offset from the
radio emission; (iii) at the eastern relic, we detect a temperature jump
corresponding to a Mach number of approximately 2.5, but there is no associated
surface brightness discontinuity. We discuss possible explanations for these
findings. | Molecular gas in the inner 0.7kpc-radius ring of M31: The study of the gas kinematic in the central 1.5kpc x 1.5kpc region of M31
has revealed several surprises. The starting point of this investigation was
the detection at the IRAM-30m telescope of molecular gas with very large line
splittings up to 260km/s within the beam (40 pc). In this region, which is
known for its low gas content, we also detect an ionised gas outflow in the
circumnuclear region (within 75pc from the centre) extending to the whole area
in X-ray. Relying on atomic, ionised, and molecular gas, we account for most
observables with a scenario that assumes that a few hundreds Myr ago, M31
underwent a frontal collision with M32, which triggered some star-formation
activity in the centre, and this collision explains the special configuration
of M31 with two rings observed at 0.7kpc and 10kpc. The inner disc (whose
rotation is detected in HI and ionised gas ([NII])) has thus been tilted
(inclination: 43deg, PA: 70deg) with respect to the main disc (inclination:
77deg, PA: 35deg). One of the CO velocity components is compatible with this
inner disc, while the second one comes from a tilted ring-like material with
40deg inclination and PA=-35deg. The relic star formation estimated by previous
works to have occurred more than 100Myr ago could have been triggered by the
collision and could be linked to the outflow detected in the ionised gas. Last,
we demonstrate that the amplitude of the line splittings detected in CO centred
on the systemic velocity with a relatively high spatial resolution (40pc)
cannot be accounted for by a possible weak bar that is roughly aligned along
the minor axis. Although M31 has a triaxial bulge, there are no bar indicators
in the gas component (photometry, no strong skewness of the isovelocities,
etc.). |
The Near-IR Luminosity Function and Bimodal Surface Brightness
Distribution of Virgo Cluster Galaxies: We have acquired deep, H-band, imaging for a sample of 286 Virgo cluster
galaxies with B <= 16 mag and extracted surface photometry from optical g,r,i,z
Sloan Digital Sky Survey images of 742 Virgo Cluster Catalog galaxies,
including those with H-band images. We confirm the detection of a dip in the
luminosity function indicative of a discontinuity in the cluster galaxy
population; the dip is more pronounced at redder wavelengths. We find, in
agreement with earlier works of Tully & Verheijen and ours for Ursa Major
cluster galaxies, a clear dichotomy between high and low surface brightness
galaxy disks. The difference between the low and high brightness peaks of Virgo
disk galaxies is ~2 H-mag arcsec^-2, significantly larger than any systematic
errors. The high surface brightness disk galaxies have two distinct classes of
high and low concentration bulges, while low surface brightness galaxies have
only low concentration bulges. Early-type galaxies exhibit a similar structural
bimodality though offset from that of the spiral galaxies towards higher
surface brightnesses. Both the early- and late-type structural bimodalities are
uncorrelated with colour or any other structural parameter except, possibly,
circular velocity. The structural bimodality may be linked to dynamical
properties of galaxies. Low angular momentum systems may collapse to form
dynamically important disks with high surface brightness, while high angular
momentum systems would end up as low surface brightness galaxies dominated by
the dark halo at all radii. The confirmation of structural bimodality for
gas-rich and gas-poor galaxies in the high-density Virgo cluster as well as the
low-density UMa cluster suggests that this phenomenon is independent of
environment. | LoCuSS: Probing Galaxy Transformation Physics with Herschel: We present an early broad-brush analysis of Herschel/PACS observations of
star-forming galaxies in 8 galaxy clusters drawn from our survey of 30 clusters
at z~0.2. We define a complete sample of 192 spectroscopically confirmed
cluster members down to L_TIR>3x10^10L_sun and L_K>0.25L_sun. The average
K-band and bolometric infrared luminosities of these galaxies both fade by a
factor of ~2 from clustercentric radii of 2r_200 to ~0.5r_200, indicating that
as galaxies enter the clusters ongoing star-formation stops first in the most
massive galaxies, and that the specific star-formation rate (SSFR) is
conserved. On smaller scales the average SSFR jumps by 25%, suggesting that in
cluster cores processes including ram pressure stripping may trigger a final
episode of star-formation that presumably exhausts the remaining gas. This
picture is consistent with our comparison of the Herschel-detected cluster
members with the cluster mass distributions, as measured in our previous
weak-lensing study of these clusters. For example, the spatial distribution of
the Herschel sources is positively correlated with the structures in the
weak-lensing mass maps at 5sigma significance, with the strongest signal seen
at intermediate group-like densities. The strong dependence of the total
cluster IR luminosity on cluster mass L_TIR propto M_virial^2 is also
consistent with accretion of galaxies and groups of galaxies (i.e. the
substructure mass function) driving the cluster IR luminosity. The most
surprising result is that roughly half of the Herschel-detected cluster members
have redder S_100/S_24 flux ratios than expected, based on the Rieke et al.
models. On average cluster members are redder than non-members, and the
fraction of red galaxies increases towards the cluster centers, both of which
indicate that these colors are not attributable to systematic photometric
errors. [Abridged] |
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