495 research outputs found
Details of the mass--temperature relation for clusters of galaxies
We present results on the total mass and temperature determination using two
samples of clusters of galaxies. One sample is constructed with emphasis on the
completeness of the sample, while the advantage of the other is the use of the
temperature profiles, derived with ASCA. We obtain remarkably similar fits to
the M-T relation for both samples, with the normalization and the slope
significantly different from both prediction of self-similar collapse and
hydrodynamical simulations. We discuss the origin of these discrepancies and
also combine the X-ray mass with velocity dispersion measurements to provide a
comparison with high-resolution dark matter simulations. Finally, we discuss
the importance of a cluster formation epoch in the observed M-T relation.Comment: 12 pages, A&A 2001 in pres
The RASS-SDSS galaxy cluster survey
Solid observational evidences indicate a strong dependence of the galaxy
formation and evolution on the environment. In order to study in particular the
interaction between the intracluster medium and the evolution of cluster
galaxies, we have created a large database of clusters of galaxies based on the
largest available X-ray and optical surveys: the ROSAT All Sky Survey (RASS),
and the Sloan Digital Sky Survey (SDSS). We analyzed the correlation between
the total optical and the X-ray cluster luminosity. The resulting correlation
of L_X and L_{op} shows a logarithmic slope of 0.6, a value close to the
self-similar correlation. We analysed also the cluster mass to light ratio, by
finding a significant dependence of M/L on the cluster mass with a logarithmic
slope ranging from 0.27 in the i and r bands to 0.22 in the z band.Comment: proceedings of 'Multiwavelength mapping of galaxy evolution'
conference held in Venice (Italy), October 2003, A. Renzini and R. Bender
(Eds.), 2 pages, 1 figur
Diffuse radio emission in a REFLEX cluster
Deep Very Large Array radio observations are presented for the REFLEX
clusters RXCJ0437.1+0043 and RXCJ1314.4-2515. They are at similar distance and
show similar X-ray luminosity, but they are quite different in X-ray structure.
Indeed RXCJ0437.1+0043 is regular and relaxed, whereas RXCJ1314.4-2515 is
characterized by substructure and possible merging processes. The radio images
reveal no diffuse emission in RXCJ0437.1+0043, and a complex diffuse structure
in RXCJ1314.4-2515. The diffuse source in the latter cluster consists of a
central radio halo which extends to the West toward the cluster periphery and
bends to the North to form a possible relic. Another extended source is
detected in the eastern cluster peripheral region. Although there could be
plausible optical identifications for this source, it might also be a relic
candidate owing to its very steep spectrum. The present results confirm the
tight link between diffuse cluster radio sources and cluster merger processes.Comment: Accepted for publication in A&A. Figures here have been degraded to
reduce their size. A version with full resolution figures is available at
http://www.ira.cnr.it/~lferetti/OUTGOING/papREFLEX.ps.g
Suzaku observations of the low surface brightness cluster A76
Context: We present results of Suzaku observations of a nearby galaxy cluster
A76 at z=0.0395. This cluster is characterized by extremely low X-ray surface
brightness and is hereafter referred to as the LSB cluster. Aims: To understand
the nature and thermodynamic evolution of the LSB cluster by studying the
physical properties of the hot intracluster medium in A76. Methods: We
conducted two-pointed Suzaku observations of A76 and examined the global gas
properties of the cluster by XIS spectral analysis. We also performed
deprojection analysis of annular spectra and derived radial profiles of gas
temperature, density and entropy out to approximately 850 kpc (~ 0.6 r_200) and
560 kpc (~0.4 r_200) in A76 East and A76 West, respectively. Results: The
measured global temperature and metal abundance are approximately 3.3 keV and
0.24 solar, respectively. From the deprojection analysis, the entropy profile
is found to be flat with respect to radius. The entropy within the central
region (r < 0.2r_200) is exceptionally high (~400 keV cm^2). This phenomenon is
not readily explained by either gravitational heating or preheating. The X-ray
morphology is clumped and irregular, and the electron density is extremely low
(1e-4 -- 1e-3 cm^-3) for the observed high temperature, suggesting that A76 is
in the early phase of cluster formation and the gas compression due to
gravitational potential confinement is lagging behind the gas heating.Comment: 7 pages, 5 figures, A&A accepte
Probing Turbulence in the Coma Galaxy Cluster
Spatially-resolved gas pressure maps of the Coma galaxy cluster are obtained
from a mosaic of XMM-Newton observations in the scale range between a
resolution of 20 kpc and an extent of 2.8 Mpc. A Fourier analysis of the data
reveals the presence of a scale-invariant pressure fluctuation spectrum in the
range between 40 and 90 kpc and is found to be well described by a projected
Kolmogorov/Oboukhov-type turbulence spectrum. Deprojection and integration of
the spectrum yields the lower limit of percent of the total
intracluster medium pressure in turbulent form. The results also provide
observational constraints on the viscosity of the gas.Comment: 12 pages, 13 figures (low resolution), version accepted by Astron.
Astrophy
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