Soft X-ray excess emission in clusters of galaxies observed with XMM-Newton

Abstract

We present results on the spectroscopic analysis of XMM-Newton EPIC data of the central 0.5/h_50 Mpc regions of the clusters of galaxies Coma, A1795 and A3112. The temperature of the hot intracluster gas as determined by modeling the 2 - 7 keV PN and MOS data is consistent with that inferred from the FeXXV-FeXXVI line ratio. A significant warm emission component at a level above the systematic uncertainties is evident in the data and confirmed by ROSAT PSPC data for Coma and A1795. The non-thermal origin of the phenomenon cannot be ruled out at the current level of calibration accuracy, but the thermal model fits the data significantly better, with temperatures in the range of 0.6 -- 1.3 keV and electron densities of the order of 10^{-4} -- 10^{-3} cm^{-3}. In the outer parts of the clusters the properties of the warm component are marginally consistent with the results of recent cosmological simulations, which predict a large fraction of the current epoch's bayons located in a warm-hot intergalactic medium (WHIM). However, the derived densities are too high in the cluster cores, compared to WHIM simulations, and thus more theoretical work is needed to fully understand the origin of the observed soft X-ray excess.