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 $\sim 10$ 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