X-Raying A2125: A Large-Scale Hierarchical Complex of Galaxies and Hot Gas

Abstract

We present an 82 ks Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low surface brightness X-ray emission at z=0.247. This high-resolution Chandra observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-scale diffuse hot gas. We detect 99 X-ray sources in a 17^'×17^' field. Ten of these sources are identified as members of the complex and are mostly radio-bright. Whereas unresolved X-ray sources tend to be associated with galaxies in intermediate density environments, extended X-ray emission peak at bright radio galaxies in the central cluster. In particular, a distinct X-ray trail appears on one side of the fast-moving galaxy C153, clearly due to ram pressure stripping. The diffuse X-ray emission from the central cluster can be characterized by a thermal plasma with a characteristic temperature of 3.2^+0.5_-0.4 keV and a heavy element abundance of 0.24^+0.15_-0.12 solar (90% confidence uncertainties). In comparison, a patch of low surface brightness X-ray emission apparently originates in relatively low density intergalactic gas with a characteristic temperature of 0.98^+0.22_-0.27 keV and an abundance of <~0.09 solar. The Chandra observation, together with extensive multiwavelength data, indicates that the complex represents a projection of several galaxy substructures, which may be undergoing major mergers. We discuss the dynamic states of the complex and its substructures, as well as properties of X-ray-emitting galaxies and the relationship to their environments.