Dynamical Evolution Diagnostics of Compact Galaxy Groups & Isolated Systems
Chris Fuse (TCU) , Pamela Marcum (NASA HQ,TCU), Michael Fanelli (TCU)
Compact groups contain galaxies within dense galactic environments, typically with separations less than a few diameters. Due to their short dynamical timescales, these systems are excellent probes of merging and interaction phenomena. Compact groups are the likely precursors to “fossil groups” and highly isolated elliptical galaxies. The morphology of hot gas is uniquely suited for distinguishing isolated ellipticals with a merged group origin from systems which evolved along alternative paths. As part of a larger study to understand the origin and evolution of isolated early-type galaxies identified in the Sloan Digital Sky Survey, we have analyzed the diffuse x-ray emission of 11 Hickson Compact Groups (HCG) and several isolated early-type systems, using archival data from NASA’s Chandra X-ray Observatory. We use the morphology and physical extent of the soft (0.3-2.5 keV) emission, x-ray luminosity, and gas temperature as diagnostics of the dynamical state of these systems. Correlations of x-ray measurements with other group properties provide a tool for assessing dynamical evolution, which can be used to infer the properties of the precursors of isolated ellipticals. A hot intergroup medium is not detected in 5 groups. Most of the members of these spiral-dominated groups exhibit axisymmetric x-ray emission, suggesting that this gas has experienced few external perturbations. The remaining 6 contain an intergroup medium, which extends beyond the optical extent of individual galaxies and shows significant structure. The x-ray luminosity of these groups ranges from 6.8 x 10^39 to 8 x 10^41 ergs/sec, with gas temperatures ranging from 0.62 keV kT 1.1 keV. The HCGs are observed to have sub-solar abundance values. This project is supported by NASA’s Astrophysical Data Program, grant # NNG05C53G, and a Texas Space Grant Consortium fellowship.