932 research outputs found
The enrichment history of the intracluster medium: a Bayesian approach
This work measures the evolution of the iron content in galaxy clusters by a
rigorous analysis of the data of 130 clusters at 0.1<z<1.3. This task is made
difficult by a) the low signal-to-noise ratio of abundance measurements and the
upper limits, b) possible selection effects, c) boundaries in the parameter
space, d) non-Gaussian errors, e) the intrinsic variety of the objects studied,
and f) abundance systematics. We introduce a Bayesian model to address all
these issues at the same time, thus allowing cross-talk (covariance). On
simulated data, the Bayesian fit recovers the input enrichment history, unlike
in standard analysis. After accounting for a possible dependence on X-ray
temperature, for metal abundance systematics, and for the intrinsic variety of
studied objects, we found that the present-day metal content is not reached
either at high or at low redshifts, but gradually over time: iron abundance
increases by a factor 1.5 in the 7 Gyr sampled by the data. Therefore, feedback
in metal abundance does not end at high redshift. Evolution is established with
a moderate amount of evidence, 19 to 1 odds against faster or slower metal
enrichment histories. We quantify, for the first time, the intrinsic spread in
metal abundance, 18+/-3 %, after correcting for the effect of evolution, X-ray
temperature, and metal abundance systematics. Finally, we also present an
analytic approximation of the X-ray temperature and metal abundance likelihood
functions, which are useful for other regression fitting involving these
parameters. The data for the 130 clusters and code used for the stochastic
computation are provided with the paper.Comment: A&A, in pres
Making the observational parsimonious richness a working mass proxy
Richness, i.e., the number of bright cluster galaxies, is known to correlate
with the cluster mass, however, to exploit it as mass proxy we need a way to
estimate the aperture in which galaxies should be counted that minimizes the
scatter between mass and richness. In this work, using a sample of 39 clusters
with accurate caustic masses at 0.1<z<0.22, we first show that the scatter
between mass and richness derived from survey data is negligibly small, as
small as best mass proxies. The scatter turns out to be smaller than in some
previous works and has a 90% upper limit of 0.05 dex in mass. The current
sample, adjoining 76 additional clusters analyzed in previous works,
establishes an almost scatterless, minimally evolving (if at all),
mass-richness scaling in the redshift range 0.03<z<0.55. We then exploit this
negligible scatter to derive the reference aperture to be used to compute
richness and to predict the mass of cluster samples. These predicted masses
have a total 0.16 dex scatter with caustic mass, about half of which is not
intrinsic to the proxy, but related to the noisiness of the caustic masses used
for test proxy performances. These results make richness-based masses of best
quality and available for large samples at a low observational cost.Comment: A&A, in pres
Dim galaxies and outer halos of galaxies missed by 2MASS ? The near-infrared luminosity function and density
By using high-resolution and deep Ks band observations of early-type galaxies
of the nearby Universe and of a cluster at z=0.3 we show that the two
luminosity functions (LFs) of the local universe derived from 2MASS data miss a
fair fraction of the flux of the galaxies (more than 20 to 30%) and a whole
population of galaxies of central brightness fainter than the isophote used for
detection, but bright enough to be included in the published LFs. In
particular, the fraction of lost flux increases as the galaxy surface
brightness become fainter. Therefore, the so far derived LF slopes and
characteristic luminosity as well as luminosity density are underestimated.
Other published near-infrared LFs miss flux in general, including the LF of the
distant field computed in a 3 arcsec aperture.Comment: A&A in pres
The stellar mass fraction and baryon content of galaxy clusters and groups
[Abridged] The analysis of a sample of 52 clusters with precise and
hypothesis-parsimonious measurements of mass shows that low mass clusters and
groups are not simple scaled-down versions of their massive cousins in terms of
stellar content: lighter clusters have more stars per unit cluster mass. The
same analysis also shows that the stellar content of clusters and groups
displays an intrinsic spread at a given cluster mass, i.e. clusters are not
similar each other in the amount of stars they contain, not even at a fixed
cluster mass. The stellar mass fraction depends on halo mass with (logarithmic)
slope -0.55+/-0.08 and with 0.15+/-0.02 dex of intrinsic scatter at a fixed
cluster mass. The intrinsic scatter at a fixed cluster mass we determine for
gas mass fractions is smaller, 0.06+/-0.01 dex. The intrinsic scatter in both
the stellar and gas mass fractions is a distinctive signature that the regions
from which clusters and groups collected matter, a few tens of Mpc, are yet not
representative, in terms of gas and baryon content, of the mean matter content
of the Universe. The observed stellar mass fraction values are in marked
disagreement with gasdynamics simulations with cooling and star formation of
clusters and groups. We found the the baryon (gas+stellar) fraction is fairly
constant for clusters and groups with 13.7<lg(mass)<15.0 solar masses and it is
offset from the WMAP-derived value by about 6 sigmas. The offset could be
related to the possible non universality of the baryon fraction pointed out by
our measurements of the intrinsic scatter. Our analysis is the first that does
not assume that clusters are identically equal at a given halo mass and it is
also more accurate in many aspects. The data and code used for the stochastic
computation are distributed with the paper.Comment: MNRAS, in pres
A low-scatter survey-based mass proxy for clusters of galaxies
Estimates of cosmological parameters using galaxy clusters have the scatter
in the observable at a given mass as a fundamental parameter. This work
computes the amplitude of the scatter for a newly introduced mass proxy, the
product of the cluster total luminosity times the mass-to-light ratio, usually
referred as stellar mass. The analysis of 12 galaxy clusters with excellent
total masses shows a tight correlation between the stellar mass, or stellar
fraction, and total mass within r500 with negligible intrinsic scatter: the 90%
upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is
similar to the one of best-determined mass proxies, such as Yx, i.e. the
product of X-ray temperature and gas mass. The size of the cluster sample used
to determine the intrinsic scatter is small, as in previous works proposing
low-scatter proxies because very accurate masses are needed to infer very small
values of intrinsic scatter. Three-quarters of the studied clusters have lgM
<~14 Msol, which is advantageous from a cosmological perspective because these
clusters are far more abundant than more massive clusters. At the difference of
other mass proxies such as Yx, stellar mass can be determined with survey data
up to at least z=0.9 using upcoming optical near-infrared surveys, such as DES
and Euclid, or even with currently available surveys, covering however smaller
solid angles. On the other end, the uncertainty about the predicted mass of a
single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This
is largely because the proxy itself has ~0.10 dex errors for clusters of lgM<~
14 Msol mass.Comment: A&A in pres
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