126 research outputs found
Mass profiles and concentration-dark matter relation in X-ray luminous galaxy clusters
(Abriged) Assuming that the hydrostatic equilibrium holds between the
intracluster medium and the gravitational potential, we constrain the NFW
profiles in a sample of 44 X-ray luminous galaxy clusters observed with
XMM-Newton in the redshift range 0.1-0.3. We evaluate several systematic
uncertainties that affect our reconstruction of the X-ray masses. We measure
the concentration c200, the dark mass M200 and the gas mass fraction within
R500 in all the objects of our sample, providing the largest dataset of mass
parameters for galaxy clusters in this redshift range. We confirm that a tight
correlation between c200 and M200 is present and in good agreement with the
predictions from numerical simulations and previous observations. When we
consider a subsample of relaxed clusters that host a Low-Entropy-Core (LEC), we
measure a flatter c-M relation with a total scatter that is lower by 40 per
cent. From the distribution of the estimates of c200 and M200, with associated
statistical (15-25%) and systematic (5-15%) errors, we use the predicted values
from semi-analytic prescriptions calibrated through N-body numerical runs and
measure sigma_8*Omega_m^(0.60+-0.03)= 0.45+-0.01 (at 2 sigma level, statistical
only) for the subsample of the clusters where the mass reconstruction has been
obtained more robustly, and sigma_8*Omega_m^(0.56+-0.04) = 0.39+-0.02 for the
subsample of the 11 more relaxed LEC objects. With the further constraint from
the fgas distribution in our sample, we break the degeneracy in the
sigma_8-Omega_m plane and obtain the best-fit values sigma_8~1.0+-0.2
(0.75+-0.18 when the subsample of the more relaxed objects is considered) and
Omega_m = 0.26+-0.01.Comment: 21 pages. A&A in press. Minor revisions to match accepted version.
Corrected 2nd and 3rd column in Table 3, and equation (A.4
Cool core remnants in galaxy clusters
X ray clusters are conventionally divided into two classes: "cool core" (CC)
and "non cool core" (NCC) objects, on the basis of the observational properties
of their central regions. Recent results have shown that the cluster population
is bimodal (Cavagnolo et al. 2009). We want to understand whether the observed
distribution of clusters is due to a primordial division into two distinct
classes rather than to differences in how these systems evolve across cosmic
time. We systematically search the ICM of NCC clusters in a subsample of the
B55 flux limited sample of clusters for regions which have some characteristics
typical of cool cores, namely low entropy gas and high metal abundance We find
that most NCC clusters in our sample host regions reminiscent of CC, i. e.
characterized by relative low entropy gas (albeit not as low as in CC systems)
and a metal abundance excess. We have dubbed these structures "cool core
remnants", since we interpret them as what remains of a cool core after a
heating event (AGN giant outbursts in a few cases and more commonly mergers).
We infer that most NCC clusters have undergone a cool core phase during their
life. The fact that most cool core remnants are found in dynamically active
objects provides strong support to scenarios where cluster core properties are
not fixed "ab initio" but evolve across cosmic time.Comment: Accepted for publication in Astronomy & Astrophysics. Version with
full resolution figures available at:
http://www.iasf-milano.inaf.it/~rossetti/public/CCR/rossetti.pd
Galaxy cluster outskirts: a universal entropy profile for relaxed clusters?
We fit a functional form for a universal ICM entropy profile to the scaled
entropy profiles of a catalogue of X-ray galaxy cluster outskirts results,
which are all relaxed cool core clusters at redshift below 0.25. We also
investigate the functional form suggested by Lapi et al. and Cavaliere et al.
for the behaviour of the entropy profile in the outskirts and find it to fit
the data well outside 0.3r200 . We highlight the discrepancy in the entropy
profile behaviour in the outskirts between observations and the numerical
simulations of Burns et al., and show that the entropy profile flattening due
to gas clumping calculated by Nagai & Lau is insufficient to match
observations, suggesting that gas clumping alone cannot be responsible for all
of the entropy profile flattening in the cluster outskirts. The entropy
profiles found with Suzaku are found to be consistent with ROSAT, XMM-Newton
and Planck results.Comment: 5 pages, 5 figures. Accepted for publication in MNRA
X-ray observations of PKS 0745-191 at the virial radius: Are we there yet?
We wish to reassess the properties of the ICM at large radii in the galaxy
cluster PKS 0745-191 in light of the recent Suzaku measurements. We analyze an
archival 10.5 ksec ROSAT/PSPC observation to extract the surface-brightness
profile of PKS 0745-191 and infer the deprojected density profile. We then
compare the ROSAT surface-brightness profile with the Suzaku result. We perform
a mass analysis combining the ROSAT density profile and the published
temperature profiles from different instruments. We find that the ROSAT
surface-brightness profile is statistically inconsistent (7.7 sigma) with the
Suzaku result around and beyond the value of r200 estimated by Suzaku. We argue
that, thanks to its large field of view and low background, ROSAT/PSPC is to
the present day the most sensitive instrument to low surface-brightness X-ray
emission in the 0.4-2.0 keV band. We also note that the Suzaku temperature and
mass profiles are at odds with the results from at least two other satellites
(XMM-Newton and Swift). The difference in surface brightness between ROSAT and
Suzaku is most likely explained by the existence of additional foreground
components at the low Galactic latitude of the source, which were not taken
into account in the Suzaku background modeling. In light of our mass analysis,
we conclude that any estimate of the fraction of the virial radius reached by
X-ray measures is affected by systematic errors of the order of 25%. As a
result, the properties of the ICM at the virial radius are still uncertain, and
the Suzaku results should be considered with caution.Comment: 6 pages, 5 figures, accepted for publication in A&
The gas distribution in the outer regions of galaxy clusters
We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy
clusters with the aim of measuring the density of the X-ray emitting gas in
cluster outskirts. We compare our results with numerical simulations to set
constraints on the azimuthal symmetry and gas clumping in the outer regions of
galaxy clusters. We exploit the large field-of-view and low instrumental
background of ROSAT/PSPC to trace the density of the intracluster gas out to
the virial radius. We perform a stacking of the density profiles to detect a
signal beyond r200 and measure the typical density and scatter in cluster
outskirts. We also compute the azimuthal scatter of the profiles with respect
to the mean value to look for deviations from spherical symmetry. Finally, we
compare our average density and scatter profiles with the results of numerical
simulations. As opposed to some recent Suzaku results, and confirming previous
evidence from ROSAT and Chandra, we observe a steepening of the density
profiles beyond \sim r500. Comparing our density profiles with simulations, we
find that non-radiative runs predict too steep density profiles, whereas runs
including additional physics and/or treating gas clumping are in better
agreement with the observed gas distribution. We report for the first time the
high-confidence detection of a systematic difference between cool-core and
non-cool core clusters beyond \sim 0.3r200, which we explain by a different
distribution of the gas in the two classes. Beyond \sim r500, galaxy clusters
deviate significantly from spherical symmetry, with only little differences
between relaxed and disturbed systems. We find good agreement between the
observed and predicted scatter profiles, but only when the 1% densest clumps
are filtered out in the simulations. [Abridged]Comment: The data for the average profiles and individual clusters can be
downloaded at:
http://www.isdc.unige.ch/~deckert/newsite/The_Planck_ROSAT_project.htm
XMM-Newton observations of the merging galaxy cluster CIZA J2242.8+5301
We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301
using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long,
~50-kpc wide radio relic that has been nicknamed the "Sausage". A smaller, more
irregular counter-relic is also present, along with a faint giant radio halo.
We analysed the distribution of the ICM physical properties, and searched for
shocks by trying to identify density and temperature discontinuities. East of
the southern relic, we find evidence of shock compression corresponding to a
Mach number of 1.3, and speculate that the shock extends beyond the length of
the radio structure. The ICM temperature increases at the northern relic. More
puzzling, we find a "wall" of hot gas east of the cluster centre. A partial
elliptical ring of hot plasma appears to be present around the merger. While
radio observations and numerical simulations predict a simple merger geometry,
the X-ray results point towards a more complex merger scenario.Comment: Extensively revised and expanded, with 18 pages and 17 figure
the influence of nanoscale morphology on the resistivity of cluster assembled nanostructured metallic thin films
We have studied in situ the evolution of the electrical resistivity of Fe, Pd, Nb, W and Mo cluster-assembled films during their growth by supersonic cluster beam deposition. We observed resistivity of cluster-assembled films several orders of magnitude larger than the bulk, as well as an increase in resistivity by increasing the film thickness in contrast to what was observed for atom-assembled metallic films. This suggests that the nanoscale morphological features typical of ballistic films growth, such as the minimal cluster?cluster interconnection and the evolution of surface roughness with thickness, are responsible for the observed behaviour
Richness Dependence of the Recent Evolution of Clusters of Galaxies
We revisit the issue of the recent dynamical evolution of clusters of
galaxies using a sample of ACO clusters with z<0.14, which has been selected
such that it does not contain clusters with multiple velocity components nor
strongly merging or interacting clusters, as revealed in X-rays. We use as
proxies of the cluster dynamical state the projected cluster ellipticity,
velocity dispersion and X-ray luminosity. We find indications for a recent
dynamical evolution of this cluster population, which however strongly depends
on the cluster richness. Poor clusters appear to be undergoing their primary
phase of virialization, with their ellipticity increasing with redshift with a
rate de/dz ~ 2.5, while the richest clusters show an ellipticity evolution in
the opposite direction (with de/dz ~ -1.2), which could be due to secondary
infall. When taking into account sampling effects due to the magnitude-limited
nature of the ACO cluster catalogue we find no significant evolution of the
cluster X-ray luminosity, while the velocity dispersion increases with
decreasing redshift, independent of the cluster richness, at a rate dsigma/dz ~
-1700 km/sec.Comment: 10 pages, MNRAS in pres
The Radial Dependence of Temperature and Iron Abundance: Galaxy Clusters from z=0.14 to z=0.89
Using archival Chandra and XMM-Newton data on 35 galaxy clusters, we measured
average temperature and metallicity profiles for clusters based separated by
temperature, cooling time, and redshift. Our results show no evidence for
significant changes in the metallicity or temperature profiles with redshift
once these selection effects are taken into account.Comment: 13 pages, 4 figures, v2 simply changes the acceptance date from
\today to June 6, 200
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