RENATO A. DUPKE and JOEL N. BREGMAN .ps .pdf
We report the results of spatially resolved X-ray spectroscopy of 8 different ASCApointings distributed symmetrically around the center of the Perseus cluster. The outer region of the intracluster gas is roughly isothermal, with temperature $\sim$ 6--7 keV, and metal abundance $\sim$ 0.3 Solar. Spectral analysis of the central pointing is consistent with the presence of a cooling flow and a central metal abundance gradient. A significant velocity gradient is found along an axis highly discrepant with the major axis of the X-ray elongation. The radial velocity difference is found to be greater than 1000 km s$^{-1}Mpc^{-1}$ at the 90\% confidence level. Simultaneous fittings of GIS 2 \& 3 indicate that two symmetrically opposed regions have different radial velocities at the 95\% confidence level and the F-test rules out constant velocities for these regions at the 99\% level. Intrinsic short and long term variations of gain are unlikely (P $<$ 0.03) to explain the velocity discrepancies. We also report the preliminary results of a similar analysis carried out for the Centaurus cluster, where long-exposure SIS data is available. We also find a significant velocity gradient near the central regions (3$^\prime$-8$^\prime$ of Centaurus. If attributed to bulk rotation the correspondent circular velocity is $\sim$1500$\pm$150~km s$^{-1}$ (at 90\% confidence). The line of maximum velocity gradient in Centaurus is near-perpendicular to the infalling galaxy group associated with NGC 4709.}samples and on high redshift clusters.
JIMMY A. IRWIN AND JOEL N. BREGMAN .ps .pdf
We have derived azimuthally-averaged radial temperature profiles of the X-ray gas contained within 11 clusters of galaxies with redshift z=0.03-0.2 observed with BeppoSAX. Each of the 11 clusters have had their radial temperature profiles previously determined with ASCA. We find that the temperature profiles of these clusters are generally flat or increase slightly out to $\sim$30\% of the virial radius, and that a decline in temperature of 14\% out to 30\% of the virial radius is ruled out at the 99\% confidence level. This is in accordance with a previous ROSAT PSPC study and an ASCA study by White (1999), but in disagreement with an ASCA study by Markevitch et al.(1998) that found on average that cluster temperature profiles decreased significantly with radius.
We have carried out the spectro-imaging analysis of rich clusters of galaxies, such as the Coma cluster, the Ophiuchus cluster and A2319 observed by ASCA. Mean temperatures of these clusters were obtained to be 9-11 keV. X-ray images in the energy bands, 0.7-3 keV, 3-10 keV and 0.7 keV were derived by iteratively deconvolving observed data with the response function of X-ray telescope and the plasma temperature. Thus the surface brightness distribution and temperature map for these three clusters were obtained with the angular resolution of 2 arcmin and 8 arcmin, respectively. It turned out that the high temperature regions (>12 keV) are largely extended in the outer envelope and the low temperature regions (<8 keV) correspond to the image excess. These results could be interpreted by cluster-cluster and subcluster-cluster merging process. The Ophiuchus cluster significantly shows the abundance anisotropy, that is, low in the central region and high in the outer envelope.
The correlation between x-ray luminosity and x-ray temperature (the L-T relation) for galaxy clusters and groups reflects the underlying physics in their formation and evolution. We present a uniform and systematic analysis of galaxy clusters and groups observed by the ASCA x-ray satellite and preliminary results of a study of the L--T relation using this sample. Currently the sample includes more than 200 clusters with measured x-ray temperature and luminosity from ASCA GIS spectra.
DORIS M. NEUMANN, MONIQUE ARNAUD and NABILA AGHANIM .ps .pdf
Classical scaling laws from structure formation predict that X-ray emission measure profiles of clusters of galaxies are similar once scaled to virial mass and radius. In a previous paper we have shown that indeed the cluster em ission measure profiles show small scatter when we scale them to the classical laws. However, this result is contradictory to the observed LX-T relation found for clusters of galaxies, which does not follow the predicted scaling laws. The observed relation found and confirmed by many authors is close to $L_X \propto T^3$, not $L_X \propto T^2$, predicted from classical scaling. In this paper we want to investigate this ``discrepancy''. We introduce the relationship between gas mass $M_{gas}$ and $T$: $M_{gas} \propto T^{1.94}$ to explain the LX-T relation. We look at the corresponding emission measure profiles, which scale with $M_{gas}^2$. Introducing this relationship we can reduce the scatter in the emission measure profiles by a factor of 2 when compared to the classical scaling. We interpret this finding as strong indication that the gas mass deviates from classical scaling with $M_{gas} \propto T^{1.94}$. We furthermore investigate whether also distant clusters show self-similarity. For this study we look at all clusters which were observed with ROSAT with sufficient statistics and have a temperature measurement provided by ASCA with $z>0.3$. We indeed find that the emission measure profiles of these distant clusters also show a high degree of self-similarity once we scale them to virial mass and radius. This result is a hint for an evolution of the LX-T relation with redshift, since distant clusters are smaller in the self-similar picture. We also propose that the self-similarity of clusters up to high redshift might be used as an independent measure to determine the cosmological parameters $\Omega_m$ and $\Lambda$.
It has been shown that self-gravitating systems such as elliptical galaxies have a constant specific entropy and obey a scaling law relating their potential energy to their mass (see M\'arquez's talk in this workshop), properties which might be due to the physical processes involved in the formation of these structures. Since the X-ray gas in clusters is weakly dissipative, we have checked the hypothesis that it might verify similar properties. \\ We have analyzed ROSAT-PSPC images of 15 clusters, fitting the density profile of the intra-cluster gas by a Sersic law. We also found that: 1) all these clusters roughly have the same specific entropy and 2) a scaling law linking the potential energy to the mass of the X-ray gas is observed, with the same slope as that found in elliptical galaxies.\\ We also found that the Sersic law parameters (intensity, shape and scale) are correlated two by two.
S. ETTORI, S.W. ALLEN and A.C. FABIAN .ps .pdf
We present an analysis of bepposax observations of three clusters of galaxies which are amongst the most luminous in the Universe: RXJ1347-1145, Zwicky~3146 and Abell~2390. We constrain, with a relative uncertainty of between 7 and 42 per cent (90 per cent confidence level), the mean gas temperature in the three clusters. These measurements are checked against any possible non-thermal contribution to the plasma emission and are shown to be robust. We confirm that RXJ1347-1145 has a gas temperature that lies in the range between 13.2 and 22.3 keV at the 90 per cent confidence level, and is larger than 12.1 keV at $3 \sigma$ level. The existence of such a hot galaxy cluster at redshift of about 0.45 implies an upper limit on the mean mass density in the Universe, $\Omega_{\rm m}$, of 0.5.
S. ETTORI, S.W. ALLEN and A.C. FABIAN .ps .pdf
We present spatially-resolved X-ray spectroscopy of the central 300 h_{50}^{-1}$kpc of the cooling flow cluster of galaxies Abell~1795 made with the \chandra observatory. The data for the inner $\sim$ 150 kpc indicate the presence for a strong cooling flow with an integrated mass deposition rate of about 200 M yr^{-1} The plasma temperature rises moving outwards in the cluster by a factor of 2, whereas the metal abundance decreases from $0.54^{+0.06}_{-0.05}$ to 0.23^{+0.04}_{-0.07} times the solar abundance over the same radial range (1 sigma error-bar).
G.B. LIMA NETO, V. PISLAR and J. BAGCHI .ps .pdf
The Intra Cluster Medium is supposed to have been enriched by metal rich, strong galactic wind that develops early in the galaxy history. Through the analysis of BeppoSAX data of Abell 85, in the [0.15-10] keV range, we were able to obtain a low spatial resolution maps of temperature, abundance (basicly iron) and nH. We also derive alpha-elements/iron abundance ratios for the whole cluster and the central region. We obtain values higher than 1 in solar units. These results tend to support the burst model for elliptical galaxies, where type II SN may have the main role in the enrichment of the ICM. We also give new estimates of the magnetic field in Abell 85.
FREDERIC MAGNARD et al. .ps .pdf
Using simulated spectra, we estimate the biases in the parameters describing the intra-cluster plasma, as obtained from spectral fits of spatially unresolved, polytropic non-isothermal X-ray clusters and group s of galaxies for various spectro-imaging instruments on X-ray telescopes (with an emphasis on XMM-Newton). We find that for typical observational parameters, the temperature obtained from single-temperature fits is equal, within simeq 10% to the emission-weighted temperature, but underestimated but up to 20% when a cooling flow is present (high temperature clusters). These results are little affected by the metal abundance of the plasma, the signal-to-noise ratio of the observations (above some minimum, rarely reached by ROSAT/PSPC or Asca) and the spectral resolution of the instrument. Estimations of metal abundances and hydrogen absorptions are little biased , excepted in presence of a cooling flow. The residual of single temperature fits tend to be largest near 1keV and we suggest a chi2 analysis on grouped energy channels in the range 0.7 - 1.3 keV