129 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
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
The Baryon Content of Cosmic Structures
We make an inventory of the baryonic and gravitating mass in structures
ranging from the smallest galaxies to rich clusters of galaxies. We find that
the fraction of baryons converted to stars reaches a maximum between M500 =
1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright
galaxies in groups. The fraction of baryons detected in all forms deviates
monotonically from the cosmic baryon fraction as a function of mass. On the
largest scales of clusters, most of the expected baryons are detected, while in
the smallest dwarf galaxies, fewer than 1% are detected. Where these missing
baryons reside is unclear.Comment: ApJ Letters, in pres
Two fossil groups of galaxies at z~0.4 in the COSMOS: accelerated stellar-mass build-up, different progenitors
We report on 2 fossil groups of galaxies at z=0.425 and 0.372 discovered in
the Cosmic Evolution Survey (COSMOS) area. Selected as X-ray extended sources,
they have total masses (M_200) of 1.9(+/-0.41)E13 and 9.5(+/-0.42)E13 M_sun,
respectively, as obtained from a recent X-ray luminosity-mass scaling relation.
The lower mass system appears isolated, whereas the other sits in a well-known
large-scale structure (LSS) populated by 27 other X-ray emitting groups. The
identification as fossil is based on the i-band photometry of all the galaxies
with a photo-z consistent with that of the group at the 2-sigma confidence
level and within a projected group-centric distance equal to 0.5R_200, and
i_AB<=22.5-mag limited spectroscopy. Both fossil groups exhibit high
stellar-to-total mass ratios compared to all the X-ray selected groups of
similar mass at 0.3<=z<=0.5 in the COSMOS. At variance with the composite
galaxy stellar mass functions (GSMFs) of similarly massive systems, both fossil
group GSMFs are dominated by passively evolving galaxies down to M^stars~1E10
M_sun (according to the galaxy broad-band spectral energy distributions). The
relative lack of star-forming galaxies with 1E10<=M^stars<=1E11 M_sun is
confirmed by the galaxy distribution in the b-r vs i color-magnitude diagram.
Hence, the 2 fossil groups appear as more mature than the coeval, similarly
massive groups. Their overall star formation activity ended rapidly after an
accelerated build up of the total stellar mass; no significant infall of
galaxies with M^stars>=1E10 M_sun took place in the last 3 to 6 Gyr. This
similarity holds although the 2 fossil groups are embedded in two very
different density environments of the LSS, which suggests that their galaxy
populations were shaped by processes that do not depend on the LSS. However,
their progenitors may do so. ...Comment: 12 pages, 5 color figures, 1 table; to be published in the MNRA
On the Baryon Fractions in Clusters and Groups of Galaxies
We present the baryon fractions of 2MASS groups and clusters as a function of
cluster richness using total and gas masses measured from stacked ROSAT X-ray
data and stellar masses estimated from the infrared galaxy catalogs. We detect
X-ray emission even in the outskirts of clusters, beyond r_200 for richness
classes with X-ray temperatures above 1 keV. This enables us to more accurately
determine the total gas mass in these groups and clusters. We find that the
optically selected groups and clusters have flatter temperature profiles and
higher stellar-to-gas mass ratios than the individually studied, X-ray bright
clusters. We also find that the stellar mass in poor groups with temperatures
below 1 keV is comparable to the gas mass in these systems. Combining these
results with individual measurements for clusters, groups, and galaxies from
the literature, we find a break in the baryon fraction at ~1 keV. Above this
temperature, the baryon fraction scales with temperature as f_b \propto
T^0.20\pm0.03. We see significantly smaller baryon fractions below this
temperature, and the baryon fraction of poor groups joins smoothly onto that of
systems with still shallower potential wells such as normal and dwarf galaxies
where the baryon fraction scales with the inferred velocity dispersion as f_b
\propto \sigma^1.6. The small scatter in the baryon fraction at any given
potential well depth favors a universal baryon loss mechanism and a preheating
model for the baryon loss. The scatter is, however, larger for less massive
systems. Finally, we note that although the broken power-law relation can be
inferred from data points in the literature alone, the consistency between the
baryon fractions for poor groups and massive galaxies inspires us to fit the
two categories of objects (galaxies and clusters) with one relation.Comment: 21 pages, 5 figures, ApJ in pres
Modeling Extragalactic Foregrounds and Secondaries for Unbiased Estimation of Cosmological Parameters From Primary CMB Anisotropy
Using the latest physical modeling and constrained by the most recent data,
we develop a phenomenological parameterized model of the contributions to
intensity and polarization maps at millimeter wavelengths from external
galaxies and Sunyaev-Zeldovich effects. We find such modeling to be necessary
for estimation of cosmological parameters from Planck data. For example,
ignoring the clustering of the infrared background would result in a bias in
n_s of 7 sigma. We show that the simultaneous marginalization over a full
foreground model can eliminate such biases, while increasing the statistical
uncertainty in cosmological parameters by less than 20%. The small increases in
uncertainty can be significantly reduced with the inclusion of
higher-resolution ground-based data.
The multi-frequency analysis we employ involves modeling 46 total power
spectra and marginalization over 17 foreground parameters. We show that we can
also reduce the data to a best estimate of the CMB power spectra, and just two
principal components (with constrained amplitudes) describing residual
foreground contamination.Comment: 17 pages, 7 figures, submitted to Ap
The XMM-Newton Wide-Field Survey in the COSMOS Field: Statistical Properties of Clusters of Galaxies
We present the results of a search for galaxy clusters in the first 36 XMM-Newton pointings on the Cosmic Evolution Survey (COSMOS) field. We reach a depth for a total cluster flux in the 0.5-2 keV band of 3 × 10^(-15) ergs cm^(-2) s^(-1), having one of the widest XMM-Newton contiguous raster surveys, covering an area of 2.1 deg^2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. Verification of the cluster candidates is done based on a galaxy concentration analysis in redshift slices of thickness 0.1-0.2 in redshift, using the multiband photometric catalog of the COSMOS field and restricting the search to z S)-log S distribution compares well with previous results, although yielding a somewhat higher number of clusters at similar fluxes. The X-ray luminosity function of COSMOS clusters matches well the results of nearby surveys, providing a comparably tight constraint on the faint-end slope of α = 1.93 ± 0.04. For the probed luminosity range of (8 × 10^(42))-(2 × 10^(44)) ergs s^(-1), our survey is in agreement with and adds significantly to the existing data on the cluster luminosity function at high redshifts and implies no substantial evolution at these luminosities to z = 1.3
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