52 research outputs found
Infall near clusters of galaxies: comparing gas and dark matter velocity profiles
We consider the dynamics in and near galaxy clusters. Gas, dark matter and
galaxies are presently falling into the clusters between approximately 1 and 5
virial radii. At very large distances, beyond 10 virial radii, all matter is
following the Hubble flow, and inside the virial radius the matter particles
have on average zero radial velocity. The cosmological parameters are imprinted
on the infall profile of the gas, however, no method exists, which allows a
measurement of it. We consider the results of two cosmological simulations
(using the numerical codes RAMSES and Gadget) and find that the gas and dark
matter radial velocities are very similar. We derive the relevant dynamical
equations, in particular the generalized hydrostatic equilibrium equation,
including both the expansion of the Universe and the cosmological background.
This generalized gas equation is the main new contribution of this paper. We
combine these generalized equations with the results of the numerical
simulations to estimate the contribution to the measured cluster masses from
the radial velocity: inside the virial radius it is negligible, and inside two
virial radii the effect is below 40%, in agreement the earlier analyses for DM.
We point out how the infall velocity in principle may be observable, by
measuring the gas properties to distance of about two virial radii, however,
this is practically not possible today.Comment: 7 pages, 3 figures, to appear in MNRA
Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations
We use the IllustrisTNG simulations to investigate the evolution of the
mass-metallicity relation (MZR) for star-forming cluster galaxies as a function
of the formation history of their cluster host. The simulations predict an
enhancement in the gas-phase metallicities of star-forming cluster galaxies
(10^9< M_star<10^10 M_sun) at z<1.0 in comparisons to field galaxies. This is
qualitatively consistent with observations. We find that the metallicity
enhancement of cluster galaxies appears prior to their infall into the central
cluster potential, indicating for the first time a systematic "chemical
pre-processing" signature for {\it infalling} cluster galaxies. Namely,
galaxies which will fall into a cluster by z=0 show a ~0.05 dex enhancement in
the MZR compared to field galaxies at z<0.5. Based on the inflow rate of gas
into cluster galaxies and its metallicity, we identify that the accretion of
pre-enriched gas is the key driver of the chemical evolution of such galaxies,
particularly in the stellar mass range (10^9< M_star<10^10 M_sun). We see
signatures of an environmental dependence of the ambient/inflowing gas
metallicity which extends well outside the nominal virial radius of clusters.
Our results motivate future observations looking for pre-enrichment signatures
in dense environments.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Constraints on the frequency and mass content of r-process events derived from turbulent mixing in galactic disks
Metal-poor stars in the Milky Way (MW) halo display large star-to-star
dispersion in their r-process abundance relative to lighter elements. This
suggests a chemically diverse and unmixed interstellar medium (ISM) in the
early Universe. This study aims to help shed light on the impact of turbulent
mixing, driven by core collapse supernovae (cc-SNe), on the r-process abundance
dispersal in galactic disks. To this end, we conduct a series of simulations of
small-scale galaxy patches which resolve metal mixing mechanisms at parsec
scales. Our set-up includes cc-SNe feedback and enrichment from r-process
sources. We find that the relative rate of the r-process events to cc-SNe is
directly imprinted on the shape of the r-process distribution in the ISM with
more frequent events causing more centrally peaked distributions. We consider
also the fraction of metals that is lost on galactic winds and find that cc-SNe
are able to efficiently launch highly enriched winds, especially in smaller
galaxy models. This result suggests that smaller systems, e.g. dwarf galaxies,
may require higher levels of enrichment in order to achieve similar mean
r-process abundances as MW-like progenitors systems. Finally, we are able to
place novel constraints on the production rate of r-process elements in the MW,
, imposed by accurately reproducing the mean and
dispersion of [Eu/Fe] in metal-poor stars. Our results are consistent with
independent estimates from alternate methods and constitute a significant
reduction in the permitted parameter space.Comment: 20 pages, 12 figures, 3 appendices. Accepted for publication in The
Astrophysical Journa
Studying the WHIM with Gamma Ray Bursts
We assess the possibility to detect and characterize the physical state of
the missing baryons at low redshift by analyzing the X-ray absorption spectra
of the Gamma Ray Burst [GRB] afterglows, measured by a micro calorimeters-based
detector with 3 eV resolution and 1000 cm2 effective area and capable of fast
re-pointing, similar to that on board of the recently proposed X-ray satellites
EDGE and XENIA. For this purpose we have analyzed mock absorption spectra
extracted from different hydrodynamical simulations used to model the
properties of the Warm Hot Intergalactic Medium [WHIM]. These models predict
the correct abundance of OVI absorption lines observed in UV and satisfy
current X-ray constraints. According to these models space missions like EDGE
and XENIA should be able to detect about 60 WHIM absorbers per year through the
OVII line. About 45 % of these have at least two more detectable lines in
addition to OVII that can be used to determine the density and the temperature
of the gas. Systematic errors in the estimates of the gas density and
temperature can be corrected for in a robust, largely model-independent
fashion. The analysis of the GRB absorption spectra collected in three years
would also allow to measure the cosmic mass density of the WHIM with about 15 %
accuracy, although this estimate depends on the WHIM model. Our results suggest
that GRBs represent a valid, if not preferable, alternative to Active Galactic
Nuclei to study the WHIM in absorption. The analysis of the absorption spectra
nicely complements the study of the WHIM in emission that the spectrometer
proposed for EDGE and XENIA would be able to carry out thanks to its high
sensitivity and large field of view.Comment: 16 pages, 16 figures, accepted for publication by Ap
How Baryonic Processes affect Strong Lensing properties of Simulated Galaxy Clusters
The observed abundance of giant arcs produced by galaxy cluster lenses and
the measured Einstein radii have presented a source of tension for LCDM.
Previous cosmological tests for high-redshift clusters (z>0.5) have suffered
from small number statistics in the simulated sample and the implementation of
baryonic physics is likely to affect the outcome. We analyse zoomed-in
simulations of a fairly large sample of cluster-sized objects, with Mvir >
3x10^14 Msun/h, identified at z=0.25 and z=0.5, for a concordance LCDM
cosmology. We start with dark matter only simulations, and then add gas
hydrodynamics, with different treatments of baryonic processes: non-radiative
cooling, radiative cooling with star formation and galactic winds powered by
supernova explosions, and finally including the effect of AGN feedback. We find
that the addition of gas in non-radiative simulations does not change the
strong lensing predictions significantly, but gas cooling and star formation
together significantly increase the number of expected giant arcs and the
Einstein radii, particularly for lower redshift clusters and lower source
redshifts. Further inclusion of AGN feedback reduces the predicted strong
lensing efficiencies such that the lensing probability distributions becomes
closer to those obtained for simulations including only dark matter. Our
results indicate that the inclusion of baryonic physics in simulations will not
solve the arc-statistics problem at low redshifts, when the physical processes
included provide a realistic description of cooling in the central regions of
galaxy clusters. [Abridged]Comment: 19 pages, 18 figures, 1 table, Accepted for publication in MNRA
Shallow Dark Matter Cusps in Galaxy Clusters
We study the evolution of the stellar and dark matter components in a galaxy
cluster of from to the present epoch using
the high-resolution collisionless simulations of Ruszkowski & Springel (2009).
At the dominant progenitor halos were populated with spherical model
galaxies with and without accounting for adiabatic contraction. We apply a
weighting scheme which allows us to change the relative amount of dark and
stellar material assigned to each simulation particle in order to produce
luminous properties which agree better with abundance matching arguments and
observed bulge sizes at . This permits the study of the effect of initial
compactness on the evolution of the mass-size relation. We find that for more
compact initial stellar distributions the size of the final Brightest Cluster
Galaxy grows with mass according to , whereas for more extended
initial distributions, . Our results show that collisionless
mergers in a cosmological context can reduce the strength of inner dark matter
cusps with changes in logarithmic slope of 0.3 to 0.5 at fixed radius. Shallow
cusps such as those found recently in several strong lensing clusters thus do
not necessarily conflict with CDM, but may rather reflect on the initial
structure of the progenitor galaxies, which was shaped at high redshift by
their formation process.Comment: 8 pages, 4 figures, submitted to MNRA
Galactic star formation and accretion histories from matching galaxies to dark matter haloes
We present a new statistical method to determine the relationship between the
stellar masses of galaxies and the masses of their host dark matter haloes over
the entire cosmic history from z~4 to the present. This multi-epoch abundance
matching (MEAM) model self-consistently takes into account that satellite
galaxies first become satellites at times earlier than they are observed. We
employ a redshift-dependent parameterization of the stellar-to-halo mass
relation to populate haloes and subhaloes in the Millennium simulations with
galaxies, requiring that the observed stellar mass functions at several
redshifts be reproduced simultaneously. Using merger trees extracted from the
dark matter simulations in combination with MEAM, we predict the average
assembly histories of galaxies, separating into star formation within the
galaxies (in-situ) and accretion of stars (ex-situ). The peak star formation
efficiency decreases with redshift from 23% at z=0 to 9% at z=4 while the
corresponding halo mass increases from 10^11.8M\odot to 10^12.5M\odot. The star
formation rate of central galaxies peaks at a redshift which depends on halo
mass; for massive haloes this peak is at early cosmic times while for low-mass
galaxies the peak has not been reached yet. In haloes similar to that of the
Milky-Way about half of the central stellar mass is assembled after z=0.7. In
low-mass haloes, the accretion of satellites contributes little to the assembly
of their central galaxies, while in massive haloes more than half of the
central stellar mass is formed ex-situ with significant accretion of satellites
at z<2. We find that our method implies a cosmic star formation history and an
evolution of specific star formation rates which are consistent with those
inferred directly. We present convenient fitting functions for stellar masses,
star formation rates, and accretion rates as functions of halo mass and
redshift.Comment: 20 pages, 12 figures, 1 table, submitted to MNRA
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Measuring non-linear galaxy bias at z ~ 0.8
Aims. We use the first release of the VImos Public Extragalactic Redshift Survey of galaxies (VIPERS) of 3c50 000 objects to measure the biasing relation between galaxies and mass in the redshift range z = [0.5,1.1]. Methods. We estimate the 1-point distribution function [PDF] of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, we infer their mean bias relation. The reconstruction of the bias relation is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage. and other selection effects. With this procedure we constrain galaxy bias and its deviations from linearity down to scales as small as 4 h-1 Mpc and out to z = 1.1. Results. We detect small (up to 2%) but statistically significant (up to 3\u3c3) deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. This slope increases with luminosity, which is in agreement with results of previous analyses. We detect a strong bias evolution only for z> 0.9, which is in agreement with some, but not all, previous studies. We also detect a significant increase of the bias with the scale, from 4 to 8 h-1 Mpc, now seen for the first time out to z = 1. The amplitude of non-linearity depends on redshift, luminosity, and scale, but no clear trend is detected. Owing to the large cosmic volume probed by VIPERS, we find that the mismatch between the previous estimates of bias at z 3c 1 from zCOSMOS and VVDS-Deep galaxy samples is fully accounted for by cosmic variance. Conclusions. The results of our work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that non-linearities can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS. \ua9 ESO, 2016
gamma-rays from annihilating dark matter in galaxy clusters: stacking vs single source analysis
Clusters of galaxies are potentially important targets for indirect searches
for dark matter annihilation. Here we reassess the detection prospects for
annihilation in massive halos, based on a statistical investigation of 1743
clusters in the new Meta-Catalog of X-ray Clusters. We derive a new limit for
the extra-galactic dark matter annihilation background of at least 20% of that
originating from the Galaxy for an integration angle of 0.1 deg. The number of
clusters scales as a power law with their brightness, suggesting that stacking
may provide a significant improvement over a single target analysis. The mean
angle containing 80% of the dark-matter signal for the sample is ~0.15 deg,
indicating that instruments with this angular resolution or better would be
optimal for a cluster annihilation search based on stacking. A detailed study
based on the Fermi-LAT performance and position-dependent background, suggests
that stacking may result in a factor ~2 improvement in sensitivity, depending
on the source selection criteria. Based on the expected performance of CTA, we
find no improvement with stacking, due to the requirement for pointed
observations. We note that several potentially important targets: Opiuchius,
A2199, A3627 (Norma) and CIZAJ1324.7-5736 may be disfavoured due to a poor
contrast with respect to the Galactic dark-matter signal. The use of the
homogenised MCXC meta-catalogue provides a robust ranking of the targets,
although the absolute value of their signal depends on the exact dark matter
substructure content. For conservative assumptions, we find that galaxy
clusters (with or without stacking) can probe down to 1e-25-1e-24
cm3/s for dark matter masses in the range 10 GeV-100 GeV. For more favourable
substructure configurations, ~1e-26 cm3/s may be reached.Comment: 11 pages, 6+2(new) figures, impact of substructures discussed in new
Sec 3.4 (matches accepted MNRAS version). Supplementary file available at
http://lpsc.in2p3.fr/clumpy/downloads.htm
ZFIRE: Similar Stellar Growth in Hα-emitting Cluster and Field Galaxies at z ~ 2
We compare galaxy scaling relations as a function of environment at
with our ZFIRE survey where we have measured H fluxes for 90
star-forming galaxies selected from a mass-limited
[] sample based on ZFOURGE. The cluster galaxies
(37) are part of a confirmed system at z=2.095 and the field galaxies (53) are
at ; all are in the COSMOS legacy field. There is no statistical
difference between H-emitting cluster and field populations when
comparing their star formation rate (SFR), stellar mass (), galaxy
size (), SFR surface density [(H)], and stellar
age distributions. The only difference is that at fixed stellar mass, the
H-emitting cluster galaxies are larger than in
the field. Approximately 19% of the H-emitters in the cluster and 26%
in the field are IR-luminous (). Because the
LIRGs in our combined sample are times more massive than the low-IR
galaxies, their radii are % larger. To track stellar growth, we
separate galaxies into those that lie above, on, and below the H
star-forming main sequence (SFMS) using SFR dex.
Galaxies above the SFMS (starbursts) tend to have higher H SFR surface
densities and younger light-weighted stellar ages compared to galaxies below
the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field
at are growing their stellar cores. Lastly, we compare to the
(SFR-) relation from RHAPSODY cluster simulations and find the
predicted slope is nominally consistent with the observations. However, the
predicted cluster SFRs tend to be too low by a factor of which seems to
be a common problem for simulations across environment.Comment: ApJ in press; full version of Table 1 available from ApJ and upon
request. Survey websites are http://zfire.swinburne.edu.au and
http://zfourge.tamu.ed
- âŠ