[Normal Galaxies, Clusters of Galaxies -- Oral ]

NGC7618 and UGC12491: Gas-Dynamics in the Nearby Merger of Two Sub-groups

Marie Machacek, SAO
R.P. Kraft (SAO), C. Jones (SAO), W.R. Forman (SAO), P.E.J. Nulsen (SAO), S.S. Murray (SAO), M.J. Hardcastle (Univ. of Hertfordshire)

Most galaxy evolution is found to occur in moderately massive galaxy groups, that, in hierarchical models of structure formation, may themselves be merging along filaments to form more massive structures. The study of nearby examples of galaxy and subgroup mergers, where Chandra's high angular resolution allows us to directly observe X-ray edges, outflows, and tails detailing the dynamical processes at work, is key to understanding the properties of galaxies, their central supermassive black holes, and the surrounding intracluster medium observed today. We present results from two ~30 ks Chandra observations of NGC7618 and UGC12491, respectively, and a 25 ks XMM-Newton MOS+pn observation of the NGC7618/UGC12491 system, together tracing gasdynamical interactions in one of the best examples of an ongoing subgroup-subgroup merger in the local universe. We find X-ray surface brightness discontinuities and temperature asymmetries around the two dominant subgroup galaxies, NGC7618 and UGC12491, but with strikingly different morphologies. We discuss the likely origin of these gas morphologies. We use imaging and spectral analyses of the observed surface brightness and temperature features to measure the density, pressure and entropy in and surrounding NGC7618 and UGC12491 to constrain the kinematics of the merger and test models for gas stripping, 'sloshing' and entropy evolution in the sub-group gas, and possible feedback from AGN activity that may have been triggered by the merger.