677 research outputs found
Probing the dark matter profile of hot clusters and the M-T relation with XMM-Newton
We present results based on XMM-Newton observations of a small sample of hot
galaxy clusters. Making a full use of XMM-Newton's spectro-imaging
capabilities, we have extracted the radial temperature profile and gas density
profile, and with this information, calculated the total mass profile of each
cluster (under the assumption of hydrostatic equilibrium and spherical
symmetry). Comparing the individual scaled total mass profiles, we have probed
the Universality of rich cluster mass profiles over a wide range of radii (from
0.01 to 0.7 the virial radius). We have also tested the shape of cluster mass
profiles by comparing with the predicted profiles from numerical simulations of
hierarchical structure formation. We also derived the local mass-temperature
(M-T) scaling relation over a range of temperature going from 4 to 9 keV, that
we compare with theoretical predictions.Comment: 7 pages, 2 figures, Advances in Space Research in press (proceedings
of the COSPAR 2004 Assembly, Paris
Distances and Cosmology From Galaxy Cluster CMB Data
The measurement of angular diameter distance to galaxy clusters, through
combined Sunyaev-Zel'dovich (SZ) effect data with X-ray emission observations,
is now a well-known probe of cosmology. Using a combination of SZ data and a
map of the lensed CMB anisotropies by the galaxy cluster potential, we propose
an alternative geometric technique to measure distance information primarily
through cluster related multi-frequency CMB measurements. We discuss necessary
requirements to implement this measurement, potential errors including
systematic biases, and the extent to which cosmological parameters can be
extracted. While individual cluster distances are not likely to be precise,
with upcoming subarcminute resolution wide-area CMB observations, useful
information on certain cosmological parameters, such as the equation of state
of dark energy, can be obtained from a large sample of galaxy clusters.Comment: 4 pages, 2 figure
Decaying dark matter: a stacking analysis of galaxy clusters to improve on current limits
We show that a stacking approach to galaxy clusters can improve current
limits on decaying dark matter by a factor , with respect to a
single source analysis, for all-sky instruments such as Fermi-LAT. Based on the
largest sample of X-ray-selected galaxy clusters available to date (the MCXC
meta-catalogue), we provide all the astrophysical information, in particular
the astrophysical term for decaying dark matter, required to perform an
analysis with current instruments.Comment: 6 pages, 3 figures, supplementary file available on demand, accepted
for publication in PR
Calibration of the galaxy cluster M_500-Y_X relation with XMM-Newton
The quantity Y_ X, the product of the X-ray temperature T_ X and gas mass M_
g, has recently been proposed as a robust low-scatter mass indicator for galaxy
clusters. Using precise measurements from XMM-Newton data of a sample of 10
relaxed nearby clusters, spanning a Y_ X range of 10^13 -10^15 M_sun keV, we
investigate the M_500-Y_ X relation. The M_500 - Y_ X data exhibit a power law
relation with slope alpha=0.548 \pm 0.027, close to the self-similar value
(3/5) and independent of the mass range considered. However, the normalisation
is \sim 20% below the prediction from numerical simulations including cooling
and galaxy feedback. We discuss two effects that could contribute to the
normalisation offset: an underestimate of the true mass due to the HE
assumption used in X-ray mass estimates, and an underestimate of the hot gas
mass fraction in the simulations. A comparison of the functional form and
scatter of the relations between various observables and the mass suggest that
Y_ X may indeed be a better mass proxy than T_ X or M_g,500.Comment: 4 pages, 2 figures, accepted for publication in A&
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
The hot gas content of fossil galaxy clusters
We investigate the properties of the hot gas in four fossil galaxy systems
detected at high significance in the Planck Sunyaev-Zeldovich (SZ) survey.
XMM-Newton observations reveal overall temperatures of kT ~ 5-6 keV and yield
hydrostatic masses M500,HE > 3.5 x 10e14 Msun, confirming their nature as bona
fide massive clusters. We measure the thermodynamic properties of the hot gas
in X-rays (out to beyond R500 in three cases) and derive their individual
pressure profiles out to R ~ 2.5 R500 with the SZ data. We combine the X-ray
and SZ data to measure hydrostatic mass profiles and to examine the hot gas
content and its radial distribution. The average Navarro-Frenk-White (NFW)
concentration parameter, c500 = 3.2 +/- 0.4, is the same as that of relaxed
`normal' clusters. The gas mass fraction profiles exhibit striking variation in
the inner regions, but converge to approximately the cosmic baryon fraction
(corrected for depletion) at R500. Beyond R500 the gas mass fraction profiles
again diverge, which we interpret as being due to a difference in gas clumping
and/or a breakdown of hydrostatic equilibrium in the external regions. Overall
our observations point to considerable radial variation in the hot gas content
and in the gas clumping and/or hydrostatic equilibrium properties in these
fossil clusters, at odds with the interpretation of their being old, evolved
and undisturbed. At least some fossil objects appear to be dynamically young.Comment: 4 pages, 2 figures. Accepted for publication in A&
Weak Lensing of Galaxy Clusters in MOND
We study weak gravitational lensing of galaxy clusters in terms of the MOND
(MOdified Newtonian Dynamics) theory. We calculate shears and convergences of
background galaxies for three clusters (A1689, CL0024+1654, CL1358+6245) and
the mean profile of 42 SDSS (Sloan Digital Sky Survey) clusters and compare
them with observational data. The mass profile is modeled as a sum of X-ray
gas, galaxies and dark halo. For the shear as a function of the angular radius,
MOND predicts a shallower slope than the data irrespective of the critical
acceleration parameter . The dark halo is necessary to explain the data
for any and for three interpolation functions. If the dark halo is
composed of massive neutrinos, its mass should be heavier than 2 eV. However
the constraint still depends on the dark halo model and there are systematic
uncertainties, and hence the more careful study is necessary to put a stringent
constraint.Comment: 12 pages, 7 figures, references added, minor changes, accepted for
publication in Ap
The structural and scaling properties of nearby galaxy clusters - II. The M-T relation
Using a sample of ten nearby (z< 0.15), relaxed galaxy clusters in the
temperature range [2-9] keV, we have investigated the scaling relation between
the mass at various density contrasts (delta=2500,1000,500,200) and the cluster
temperature. The masses are derived from NFW-type model fits to mass profiles,
obtained under the hydrostatic assumption using precise measurements, with XMM,
at least down to delta=1000. The logarithmic slope of the M-T relation is well
constrained and is the same at all delta, reflecting the self-similarity of the
mass profiles. At delta=500, the slope of the relation for the sub-sample of
hot clusters (kT>3.5 keV) is consistent with the standard self-similar
expectation: alpha= 1.49\pm0.15. The relation steepens when the whole sample is
considered: alpha=1.71\pm0.09. The normalisation of the relation is discrepant
(by ~ 30%), at all density contrasts, with the prediction from purely
gravitation based models. Models that take into account radiative cooling and
galaxy feedback are generally in better agreement with our data. We argue that
remaining discrepancies, in particular at low delta, are more likely due to
problems with models of the ICM thermal structure rather than to an incorrect
estimate of the mass from X-ray data.Comment: 11 pages, 4 figures, A&A in press, updated to match the accepted
version (19/08/2005). Minor text clarifications, more detailed analysis of
the M-T relations in Sect 3.2, corrected typo in Table 1 (redshift) and on
cluster markers in Fig 1 legen
Structural and scaling properties of galaxy clusters: probing the physics of structure formation
We present XMM-Newton studies of the total mass, gas density, temperature and
entropy profiles in nearby hot and cool clusters, together with follow-up
observations of distant clusters from the SHARC Survey. The observed structural
and scaling properties are compared with the predictions of the self-similar
model of cluster formation. These data indicate that clusters do form a
self-similar population down to low mass and up to high redshift, and give
support to the standard picture of structure formation for the dark matter
component. However, deviations from the standard scaling laws confirm that the
specific physics of the gas component is still insufficiently understood.Comment: 9 pages, 8 figures; to be published in Memorie della Societa'
Astronomica Italiana, the Proceedings of the EPIC Consortium (held on Oct
14-16, 2003 in Palermo
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