96 research outputs found
Hubble flow variations as a test for inhomogeneous cosmology
Context. Backreactions from large-scale inhomogeneities may provide an
elegant explanation for the observed accelerated expansion of the universe
without the need to introduce dark energy. Aims. We propose a cosmological test
for a specific model of inhomogeneous cosmology, called timescape cosmology.
Using large-scale galaxy surveys such as SDSS and 2MRS, we test the variation
of expansion expected in the -CDM model versus a more generic
differential expansion using our own calibrations of bounds suggested by
timescape cosmology. Method. Our test measures the systematic variations of the
Hubble flow towards distant galaxies groups as a function of the matter
distribution in the lines of sight to those galaxy groups. We compare the
observed systematic variation of the Hubble flow to mock catalogues from the
Millennium Simulation in the case of the -CDM model, and a deformed
version of the same simulation that exhibits more pronounced differential
expansion. Results. We perform a series of statistical tests, ranging from
linear regressions to Kolmogorov-Smirnov tests, on the obtained data. They
consistently yield results preferring -CDM cosmology over our
approximated model of timescape cosmology. Conclusions. Our analysis of
observational data shows no evidence that the variation of expansion differs
from that of the standard -CDM model.Comment: 20 pages, 21 figures, accepted for publication in A&
The matter distribution in the local Universe as derived from galaxy groups in SDSS DR12 and 2MRS
Context. Friends-of-friends algorithms are a common tool to detect galaxy
groups and clusters in large survey data. In order to be as precise as
possible, they have to be carefully calibrated using mock catalogues.
Aims. We create an accurate and robust description of the matter distribution
in the local Universe using the most up-to-date available data. This will
provide the input for a specific cosmological test planned as follow-up to this
work, and will be useful for general extragalactic and cosmological research.
Methods. We created a set of galaxy group catalogues based on the 2MRS and
SDSS DR12 galaxy samples using a friends-of-friends based group finder
algorithm. The algorithm was carefully calibrated and optimised on a new set of
wide-angle mock catalogues from the Millennium simulation, in order to provide
accurate total mass estimates of the galaxy groups taking into account the
relevant observational biases in 2MRS and SDSS.
Results. We provide four different catalogues (i) a 2MRS based group
catalogue; (ii) an SDSS DR12 based group catalogue reaching out to a redshift z
= 0.11 with stellar mass estimates for 70% of the galaxies; (iii) a catalogue
providing additional fundamental plane distances for all groups of the SDSS
catalogue that host elliptical galaxies; (iv) a catalogue of the mass
distribution in the local Universe based on a combination of our 2MRS and SDSS
catalogues.
Conclusions. While motivated by a specific cosmological test, three of the
four catalogues that we produced are well suited to act as reference databases
for a variety of extragalactic and cosmological science cases. Our catalogue of
fundamental plane distances for SDSS groups provides further added value to
this paper.Comment: 31 pages, 25 figures, accepted for publication in A&
Dozens of compact and high velocity-dispersion early-type galaxies in Sloan Digital Sky Survey
Aims. We aim at finding candidates of potential survivors of high-redshift
compact galaxies in SDSS, as targets for more detailed follow-up observations.
Methods. From the virial theorem it is expected that for a given mass,
compact galaxies have stellar velocity dispersion higher than the mean due to
their smaller sizes. Therefore velocity dispersion coupled with size (or mass)
is an appropriate method to select relics, independent of the stellar
population properties. Based on these consideration we design a set of criteria
using distribution of early-type galaxies from SDSS on the
log(R)-log() plane to find the most extreme
objects on it.
Results. We find 76 galaxies at 0.05 < z < 0.2, which have properties similar
to the typical quiescent galaxies at high redshift. We study how well these
galaxies fit on well-known local universe relations of early-type galaxies such
as the fundamental plane, the red sequence or mass-size relations. As expected
from the selection criteria, the candidates are located in an extreme corner of
mass-size plane. However, they do not extend as deeply into the so-called zone
of exclusion as some of the high-redshift compact galaxies ('red nuggets')
found at high redshift, being a factor 2-3 less massive at a given intrinsic
scale size. Our candidates are systematically offset from scaling relations of
average early-type galaxies, while being in the mass-size range expected for
passive evolution of the red nuggets from their high redshift to the present.
Conclusions. The 76 selected candidates form a well suited set of objects for
further follow-up observations. We argue that selecting a high velocity
dispersion is the best way to find analogues of compact high redshift galaxies
in the local universe.Comment: 37 pages, 24 figures, accepted for publication in A&
A data compression and optimal galaxy weights scheme for Dark Energy Spectroscopic Instrument and weak lensing data sets
Combining different observational probes, such as galaxy clustering and weak lensing, is a promising technique for unveiling the physics of the Universe with upcoming dark energy experiments. The galaxy redshift sample from the Dark Energy Spectroscopic Instrument (DESI) will have a significant overlap with major ongoing imaging surveys specifically designed for weak lensing measurements: The Kilo-Degree Survey (KiDS), the Dark Energy Survey (DES), and the Hyper Suprime-Cam (HSC) survey. In this work, we analyse simulated redshift and lensing catalogues to establish a new strategy for combining high-quality cosmological imaging and spectroscopic data, in view of the first-year data assembly analysis of DESI. In a test case fitting for a reduced parameter set, we employ an optimal data compression scheme able to identify those aspects of the data that are most sensitive to cosmological information and amplify them with respect to other aspects of the data. We find this optimal compression approach is able to preserve all the information related to the growth of structures
A data compression and optimal galaxy weights scheme for Dark Energy Spectroscopic Instrument and weak lensing datasets
Combining different observational probes, such as galaxy clustering and weak
lensing, is a promising technique for unveiling the physics of the Universe
with upcoming dark energy experiments. The galaxy redshift sample from the Dark
Energy Spectroscopic Instrument (DESI) will have a significant overlap with
major ongoing imaging surveys specifically designed for weak lensing
measurements: the Kilo-Degree Survey (KiDS), the Dark Energy Survey (DES) and
the Hyper Suprime-Cam (HSC) survey. In this work we analyse simulated redshift
and lensing catalogues to establish a new strategy for combining high-quality
cosmological imaging and spectroscopic data, in view of the first-year data
assembly analysis of DESI. In a test case fitting for a reduced parameter set,
we employ an optimal data compression scheme able to identify those aspects of
the data that are most sensitive to the cosmological information, and amplify
them with respect to other aspects of the data. We find this optimal
compression approach is able to preserve all the information related to the
growth of structure; we also extend this scheme to derive weights to be applied
to individual galaxies, and show that these produce near-optimal results.Comment: 14 pages, 12 Figures, DESI collaboration articl
The AIMSS Project – III. The Stellar Populations of Compact Stellar Systems
In recent years, a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilized discriminant, their stellar population properties. Based on new spectroscopy from 8–10m telescopes, we derive ages, metallicities, and [α/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals (cEs) larger than M32. Together with a literature compilation, this provides a panoramic view of the stellar population characteristics of early-type systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the cEs depart from the mass–metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultracompact dwarfs (UCDs) changes at a few times 107 M⊙, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS internal escape velocities
Synthetic light-cone catalogues of modern redshift and weak lensing surveys waith abacussummit
The joint analysis of different cosmological probes, such as galaxy clustering and weak lensing, can potentially yield invaluable insights into the nature of the primordial Universe, dark energy, and dark matter. However, the development of high-fidelity theoretical models is a necessary stepping stone. Here, we present public high-resolution weak lensing maps on the light-cone, generated using the N-body simulation suite abacussummit, and accompanying weak lensing mock catalogues, tuned to the Early Data Release small-scale clustering measurements of the Dark Energy Spectroscopic Instrument. Available in this release are maps of the cosmic shear, deflection angle, and convergence fields at source redshifts ranging from z = 0.15 to 2.45 as well as cosmic microwave background convergence maps for each of the 25 base-resolution simulations (and Npart = 69123) as well as for the two huge simulations (and Npart = 86403) at the fiducial abacussummit cosmology. The pixel resolution of each map is 0.21 arcmin, corresponding to a healpix Nside of 16 384. The sky coverage of the base simulations is an octant until z ≈ 0.8 (decreasing to about 1800 deg2 at z ≈ 2.4), whereas the huge simulations offer full-sky coverage until z ≈ 2.2. Mock lensing source catalogues are sampled matching the ensemble properties of the Kilo-Degree Survey, Dark Energy Survey, and Hyper Suprime-Cam data sets. The mock catalogues are validated against theoretical predictions for various clustering and lensing statistics, such as correlation multipoles, galaxy-shear, and shear-shear, showing excellent agreement. All products can be downloaded via a Globus endpoint (see Data Availability section)
PROVABGS: The Probabilistic Stellar Mass Function of the BGS One-percent Survey
We present the probabilistic stellar mass function (pSMF) of galaxies in the DESI Bright Galaxy Survey (BGS), observed during the One-percent Survey. The One-percent Survey was one of DESI’s survey validation programs conducted from 2021 April to May, before the start of the main survey. It used the same target selection and similar observing strategy as the main survey and successfully observed the spectra and redshifts of 143,017 galaxies in the r 100 × more galaxies. Moreover, we present the statistical framework for subsequent population statistics measurements using BGS, which will characterize the global galaxy population and scaling relations at low redshifts with unprecedented precision
PROVABGS: The Probabilistic Stellar Mass Function of the BGS One-Percent Survey
We present the probabilistic stellar mass function (pSMF) of galaxies in the
DESI Bright Galaxy Survey (BGS), observed during the One-Percent Survey. The
One-Percent Survey was one of DESI's survey validation programs conducted from
April to May 2021, before the start of the main survey. It used the same target
selection and similar observing strategy as the main survey and successfully
observed the spectra and redshifts of 143,017 galaxies in the
magnitude-limited BGS Bright sample and 95,499 galaxies in the fainter surface
brightness and color selected BGS Faint sample over . We derive pSMFs
from posteriors of stellar mass, , inferred from DESI photometry and
spectroscopy using the Hahn et al. (2022a; arXiv:2202.01809) PRObabilistic
Value-Added BGS (PROVABGS) Bayesian SED modeling framework. We use a
hierarchical population inference framework that statistically and rigorously
propagates the uncertainties. Furthermore, we include correction weights
that account for the selection effects and incompleteness of the BGS
observations. We present the redshift evolution of the pSMF in BGS as well as
the pSMFs of star-forming and quiescent galaxies classified using average
specific star formation rates from PROVABGS. Overall, the pSMFs show good
agreement with previous stellar mass function measurements in the literature.
Our pSMFs showcase the potential and statistical power of BGS, which in its
main survey will observe >100 more galaxies. Moreover, we present the
statistical framework for subsequent population statistics measurements using
BGS, which will characterize the global galaxy population and scaling relations
at low redshifts with unprecedented precision.Comment: 25 pages, 12 figures; data used to generate figures is available at
https://doi.org/10.5281/zenodo.8018936; submitted to Ap
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