343 research outputs found
Scaling relations for galaxy clusters: properties and evolution
Well-calibrated scaling relations between the observable properties and the
total masses of clusters of galaxies are important for understanding the
physical processes that give rise to these relations. They are also a critical
ingredient for studies that aim to constrain cosmological parameters using
galaxy clusters. For this reason much effort has been spent during the last
decade to better understand and interpret relations of the properties of the
intra-cluster medium. Improved X-ray data have expanded the mass range down to
galaxy groups, whereas SZ surveys have openened a new observational window on
the intracluster medium. In addition,continued progress in the performance of
cosmological simulations has allowed a better understanding of the physical
processes and selection effects affecting the observed scaling relations. Here
we review the recent literature on various scaling relations, focussing on the
latest observational measurements and the progress in our understanding of the
deviations from self similarity.Comment: 38 pages. Review paper. Accepted for publication in Space Science
Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done
by an international team at the International Space Science Institute (ISSI)
in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and
Lensing View
On the occupation of X-ray selected galaxy groups by radio AGN since z=1.3
Previous clustering analysis of low-power radio AGN has indicated that they
preferentially live in massive groups. The X-ray surveys of the COSMOS field
have achieved a sensitivity at which these groups are directly detected out to
z=1.3. Making use of Chandra-, XMM- and VLA-COSMOS surveys we identify radio
AGN members (10**23.6 < L_1.4GHz/(W/Hz) < 10**25) of galaxy groups (10**13.2 <
M_200/M_sun < 10**14.4; 0.1<z<1.3) and study i) the radio AGN -- X-ray group
occupation statistics as a function of group mass, and ii) the distribution of
radio AGN within the groups. We find that radio AGN are preferentially
associated with galaxies close to the center (< 0.2r_200). Compared to our
control sample of group members matched in stellar mass and color to the radio
AGN host galaxies, we find a significant enhancement of radio AGN activity
associated with 10**13.6 < M_200/M_sun < 10**14 halos. We present the first
direct measurement of the halo occupation distribution (HOD) for radio AGN,
based on the total mass function of galaxy groups hosting radio AGN. Our
results suggest a possible deviation from the usually assumed power law HOD
model. We also find an overall increase of the fraction of radio AGN in galaxy
groups (<1r_200), relative to that in all environments.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Identifying dynamically young galaxy groups via wide-angle tail galaxies: A case study in the COSMOS field at z=0.53
We present an analysis of a wide-angle tail (WAT) radio galaxy located in a
galaxy group in the COSMOS field at a redshift of z=0.53 (hereafter CWAT-02).
We find that the host galaxy of CWAT-02 is the brightest galaxy in the group,
although it does not coincide with the center of mass of the system. Estimating
a) the velocity of CWAT-02, relative to the intra-cluster medium (ICM), and b)
the line-of-sight peculiar velocity of CWAT-02's host galaxy, relative to the
average velocity of the group, we find that both values are higher than those
expected for a dominant galaxy in a relaxed system. This suggests that
CWAT-02's host group is dynamically young and likely in the process of an
ongoing group merger. Our results are consistent with previous findings showing
that the presence of a wide-angle tail galaxy in a galaxy group or cluster can
be used as an indicator of dynamically young non-relaxed systems. Taking the
unrelaxed state of CWAT-02's host group into account, we discuss the impact of
radio-AGN heating from CWAT-02 onto its environment, in the context of the
missing baryon problem in galaxy groups. Our analysis strengthens recent
results suggesting that radio-AGN heating may be powerful enough to expel
baryons from galaxy groups.Comment: 8 pages, 6 figures, 1 table. Accepted for publication in Ap
A direct measurement of hierarchical growth in galaxy groups since z~1
We present the first measurement of the evolution of the galaxy group stellar
mass function (GrSMF) to redshift z>~1 and low masses (M*>10^12 Msun). Our
results are based on early data from the Carnegie-Spitzer-IMACS (CSI) Survey,
utilizing low-resolution spectra and broadband optical/near-IR photometry to
measure redshifts for a 3.6um selected sample of 37,000 galaxies over a 5.3
deg^2 area to z~1.2. Employing a standard friends-of-friends algorithm for all
galaxies more massive than log(M*/Msun)=10.5, we find a total of ~4000 groups.
Correcting for spectroscopic incompleteness (including slit collisions), we
build cumulative stellar mass functions for these groups in redshift bins at
z>0.35, comparing to the z=0 and z>0 mass functions from various group and
cluster samples. Our derived mass functions match up well with z>0.35 X-ray
selected clusters, and strong evolution is evident at all masses over the past
8 Gyr. Given the already low level of star formation activity in galaxies at
these masses, we therefore attribute most of the observed growth in the GrSMF
to group-group and group-galaxy mergers, in accordance with qualitative notions
of hierarchical structure formation. Given the factor 3-10 increase in the
number density of groups and clusters with M*>10^12 Msun since z=1 and the
strong anticorrelation between star formation activity and environmental
density, this late-time growth in group-sized halos may therefore be an
important contributor to the structural and star-formation evolution of massive
galaxies over the past 8 Gyr.Comment: 6 pages, 3 figures, submitted to ApJL. This paper is based on the
Carnegie-Spitzer-IMACS (CSI) Survey, described in more detail at
http://csi.obs.carnegiescience.ed
Baryon Content of Massive Galaxy Clusters at z=0-0.6
We study the relationship between two major baryonic components in galaxy
clusters, namely the stars in galaxies, and the ionized gas in the intracluster
medium (ICM), using 94 clusters that span the redshift range 0-0.6. Accurately
measured total and ICM masses from Chandra observations, and stellar masses
derived from the Wide-field Infrared Survey Explorer and the Two-Micron All-Sky
Survey allow us to trace the evolution of cluster baryon content in a
self-consistent fashion. We find that, within r_{500}, the evolution of the ICM
mass--total mass relation is consistent with the expectation of self-similar
model, while there is no evidence for redshift evolution in the stellar
mass--total mass relation. This suggests that the stellar mass and ICM mass in
the inner parts of clusters evolve differently.Comment: 5 pages, 4 figures; accepted for publication in ApJ Letter
Radio galaxy feedback in X-ray selected groups from COSMOS: the effect on the ICM
We quantify the importance of the mechanical energy released by
radio-galaxies inside galaxy groups. We use scaling relations to estimate the
mechanical energy released by 16 radio-AGN located inside X-ray detected galaxy
groups in the COSMOS field. By comparing this energy output to the host groups'
gravitational binding energy, we find that radio galaxies produce sufficient
energy to unbind a significant fraction of the intra-group medium. This
unbinding effect is negligible in massive galaxy clusters with deeper potential
wells. Our results correctly reproduce the breaking of self-similarity observed
in the scaling relation between entropy and temperature for galaxy groups.Comment: Accepted for publication in the Astrophysical Journal. 12 Page
Interpolating Masked Weak Lensing Signal with Karhunen-Loeve Analysis
We explore the utility of Karhunen Loeve (KL) analysis in solving practical
problems in the analysis of gravitational shear surveys. Shear catalogs from
large-field weak lensing surveys will be subject to many systematic
limitations, notably incomplete coverage and pixel-level masking due to
foreground sources. We develop a method to use two dimensional KL eigenmodes of
shear to interpolate noisy shear measurements across masked regions. We explore
the results of this method with simulated shear catalogs, using statistics of
high-convergence regions in the resulting map. We find that the KL procedure
not only minimizes the bias due to masked regions in the field, it also reduces
spurious peak counts from shape noise by a factor of ~ 3 in the cosmologically
sensitive regime. This indicates that KL reconstructions of masked shear are
not only useful for creating robust convergence maps from masked shear
catalogs, but also offer promise of improved parameter constraints within
studies of shear peak statistics.Comment: 13 pages, 9 figures; submitted to Ap
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