699 research outputs found
On the evolution of cooling cores in X-ray galaxy clusters
(Abridged) To define a framework for the formation and evolution of the
cooling cores in X-ray galaxy clusters, we study how the physical properties
change as function of the cosmic time in the inner regions of a 4 keV and 8 keV
galaxy cluster under the action of radiative cooling and gravity only. The
cooling radius, R_cool, defined as the radius at which the cooling time equals
the Universe age at given redshift, evolves from ~0.01 R200 at z>2, where the
structures begin their evolution, to ~0.05 R200 at z=0. The values measured at
0.01 R200 show an increase of about 15-20 per cent per Gyr in the gas density
and surface brightness and a decrease with a mean rate of 10 per cent per Gyr
in the gas temperature. The emission-weighted temperature diminishes by about
25 per cent and the bolometric X-ray luminosity rises by a factor ~2 after 10
Gyrs when all the cluster emission is considered in the computation. On the
contrary, when the core region within 0.15 R500 is excluded, the gas
temperature value does not change and the X-ray luminosity varies by 10-20 per
cent only. The cooling time and gas entropy radial profiles are well
represented by power-law functions. The behaviour of the inner slopes of the
gas temperature and density profiles are the most sensitive and unambiguous
tracers of an evolving cooling core. Their values after 10 Gyrs of radiative
losses, T_gas ~ r^0.4 and n_gas ~ r^(-1.2) for the hot (cool) object, are
remarkably in agreement with the observational constraints available for nearby
X-ray luminous cooling core clusters. Because our simulations do not consider
any AGN heating, they imply that the feedback process does not greatly alter
the gas density and temperature profiles as generated by radiative cooling
alone.Comment: 8 pages. MNRAS in pres
X-ray observations and mass determinations in the cluster of galaxies Cl0024+17
We present a detailed analysis of the mass distribution in the rich and
distant cluster of galaxies Cl0024+17. X-ray data come from both a deep
ROSAT/HRI image of the field (Bohringer et al. 1999) and ASCA spectral data.
Using a wide field CCD image of the cluster, we optically identify all the
faint X-ray sources, whose counts are compatible with deep X-ray number counts.
In addition we marginally detect the X-ray counter-part of the gravitational
shear perturbation detected by Bonnet et al. (1994) at a 2.5 level. A
careful spectral analysis of ASCA data is also presented. In particular, we
extract a low resolution spectrum of the cluster free from the contamination by
a nearby point source located 1.2 arcmin from the center. The X-ray temperature
deduced from this analysis is keV at the 90%
confidence level. The comparison between the mass derived from a standard X-ray
analysis and from other methods such as the Virial Theorem or the gravitational
lensing effect lead to a mass discrepancy of a factor 1.5 to 3. We discuss all
the possible sources of uncertainties in each method of mass determination and
give some indications on the way to reduce them. A complementary study of
optical data is in progress and may solve the X-ray/optical discrepancy through
a better understanding of the dynamics of the cluster.Comment: Revised version, accepted in Astronomy and Astrophysics (Main
Journal). Few changes in the discussio
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