The dynamical state of the Coma cluster with XMM-Newton

Abstract

We present in this paper a substructure and spectroimaging study of the Coma cluster of galaxies based on XMM-Newton data. XMM-Newton performed a mosaic of observations of Coma to ensure a large coverage of the cluster. We add the different pointings together and fit elliptical beta-models to the data. We subtract the cluster models from the data and look for residuals, which can be interpreted as substructure. We find several significant structures: the well-known subgroup connected to NGC 4839 in the South-West of the cluster, and another substructure located between NGC 4839 and the centre of the Coma cluster. Constructing a hardness ratio image, which can be used as a temperature map, we see that in front of this new structure the temperature is significantly increased (higher or equal 10 keV). We interpret this temperature enhancement as the result of heating as this structure falls onto the Coma cluster. We furthermore reconfirm the filament-like structure South-East of the cluster centre. This region is significantly cooler than the mean cluster temperature. We estimate the temperature of this structure to be equal or below 1 keV. A possible scenario to explain the observed features is stripping caused by the infall of a small group of galaxies located around the two galaxies NGC 4921 and NGC 4911 into the Coma cluster with a non-zero impact parameter. We also see significant X-ray depressions North and South-East of NGC 4921, which might either be linked to tidal forces due to the merger with the Western structure or connected to an older cluster merger.