Isolated early-type galaxies and the use of x-ray diagnostics to determine the evolution history of merging and merged systems

Abstract

The dissertation presented details the search for isolated early-type galaxies (IEG). A strict set of isolation criteria were employed, requiring the candidate galaxy to be separated from nearest neighbors of M _< 16.5 by a distance of 2.5 Mpc and a redshift-space separation of 350 km/s. Such extreme isolation produces galaxies well suited as laboratories for the study of galaxy evolution, absent from the continual galaxy harassment observed for galaxies in group and cluster environments. Global and surface photometry is used in verifi cation of early-type morphology of the candidate galaxies. Two-dimensional residual maps, produced by model galaxy subtractions, are used to search for fine structure as well as isophotal deviations from a perfectly elliptical shape in the candidates.^Clues provided by these analysis techniques are used to derive estimates of the past interaction history of the galaxies.^Also investigated was the viability of X-ray diagnostics to probe the evolutionary connection between compact groups, fossil groups (FG) and isolated ellipticals. Using the X-ray luminosity and gas temperatures, it was discovered that fossil groups are composed of two distinct populations. Population 1 FGs have X-ray characteristics similar to those of the compact groups and isolated ellipticals, while population 2 FGs are signi cantly hotter and more luminous. The results suggest that compact groups are the predecessors of isolated ellipticals and population 1 FGs. Population 2 FGs appear to be the remnants of a collapsed poor cluster.^The highlights of the research are summarized as: 84% of the IEGs have blue colors and spectra indicative of young stellar populations and recent star formation.^The conclusion is that the IEGs have continued to experience accretion of dwarf companions, which implies that even in extremely isolated galaxies, minor mergers strongly influence galaxy evolution. The faint nature of the IEGs, which are magnitudes fainter than previous isolated galaxy samples, imply that the IEGs are unlikely the remains of a collapsed group. Three sample galaxies are strong candidates for having a pristine nature and might serve as the near-zero interaction baseline necessary to separate the intrinsic galaxy properties and those properties induced by external interactions.