X-ray mapping the outer regions of galaxy clusters at z=0.23 and 0.45

Abstract

The thermal, chemical, and kinematic properties of the potentially multiphase circum/ intergalactic medium at the virial radii of galaxy clusters remain largely uncertain. We present an X-ray study of Abell 2246 and GMBCG J255.34805+64.23661 (z=0.23 and 0.45), two foreground clusters of the UV-bright QSO HS 1700+6416, based on 240 ks Chandra/Advanced CCD Imaging Spectrometer observations.We detect enhanced diffuse Xray emission to the projected distances beyond r200 radii of these two clusters. The large-scale X-ray emission is consistent with being azimuthally symmetric at the projected radii of the QSO (0.36 and 0.8 times the radii of the two clusters). Assuming a spherical symmetry, we obtain the de-projected temperature and density profiles of the X-ray-emitting gas. Excluding the cool cores that are detected, we find that the mean temperature of the hot gas is ̃4.0 keV forAbell 2246 and 5.5 keV forGMBCGJ255.34805+64.23661, although there are indications for temperature drop at large radii. From these results, we can estimate the density and pressure distributions of the hot gas along the QSO sightline.We further infer the radial entropy profile of Abell 2246 and compare it with the one expected from purely gravitational hierarchical structure formation. This comparison shows that the intracluster medium in the outer region of the clusters is likely in a clumpy and multiphased state. These results, together with the upcoming Hubble Space Telescope/Cosmic Origins Spectrograph observations of the QSO sightline, will enable a comprehensive investigation of the multiphase medium associated with the clusters. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.