The spatial distributions of cooling gas and intrinsic X-ray absorbing material in cooling flows

Abstract

We present the results from a study of the spatial distributions of cooling gas and intrinsic X-ray absorbing material in a sample of nearby, X-ray bright cooling flow clusters observed with the Position Sensitive Proportional Counter (PSPC) on ROSAT. Our method of analysis employs X-ray colour profiles, formed from ratios of the surface brightness profiles of the clusters in selected energy bands, and an adapted version of the deprojection code of Fabian et. al (1981). We show that all of the cooling flow clusters in our sample exhibit significant central concentrations of cooling gas. At larger radii the clusters appear approximately isothermal. In detail, the spatial distributions and emissivity of the cooling material are shown to be in excellent agreement with the predictions from the deprojection code, and can be used to constrain the ages of the cooling flows. The X-ray colour profiles also indicate substantial levels of intrinsic X-ray absorption in the clusters. The intrinsic absorption increases with decreasing radius, and is confined to the regions occupied by the cooling flows. We explore a range of likely spatial distributions for the absorbing gas and discuss the complexities involved in the measurement of column densities from X-ray data. Comparison of our results with previously reported observations made with Einstein Observatory Solid State Spectrometer (White et. al 1991) shows reasonable agreement, but requires that the absorbing material only partially covers the X-ray emitting regions. The results presented in this paper provide strong support for the standard model of inhomogeneous cooling flows in clusters of galaxies.