X-ray Emission From Dwarf Elliptical Galaxies And Galaxy Clusters

This thesis presents our two studies on the X-ray emissivities of old stellar popula-tion and X-ray emission from two galaxy clusters (A1095 and A1926), respectively.The first one focuses on the unresolved X-ray emission from old stellar populations in three Local Group dwarf elliptical galaxies (NGC147, NGC185 and NGC 205) using XMM-Newton observations. This emission originates from a collection of weak X-ray sources, mainly cataclysmic variables and coronally active binaries. Precise knowl-edge of this stellar X-ray emission is crucial not only for understanding the relevant stellar astrophysics but also for disentangling and quantifying the thermal emission from diffuse hot gas in nearby galaxies. We find that the integrated X-ray emissivi-ties of the individual dwarf ellipticals agree well with that of the Solar vicinity, sup-porting an often assumed but untested view that the X-ray emissivity of old stellar populations is quasi-universal in normal galactic environments, in which dynamical effects on the formation and destruction of binary systems are not important. The average cumulative X-ray emissivity of the dwarf ellipticals, including M32, to be L0.5-2 kev/M*= (6.0±0.5 ± 1.8) × 1027 erg s-1 M⊙-1. We also compare this value to the integrated X-ray emissivities from four Galactic globular clusters (ω Cen,47 Tuc, NGC 6266 and NGC 6397), which we derive from Chandra data, as well as to X-ray emissivities of other old stellar systems from the literature. We then discuss the role of dynamical effects in these dense stellar systems.The second one initiated a program to study the multi-phase medium in and around cluster galaxies. We present results primarily from XMM-Newton observations of two optically-selected galaxy clusters, A1095 (z≈ 0.210) and A1926 (z ≈ 0.136). We find that both of them are actually cluster pairs at similar redshifts. We characterize the tem-peratures (A1095=3.6-0.2+0.2, A1095E=3.3-0.4+0.2, A1926a=2.2-0.2+0.2, A1926b=2.0-0.4+0.9keV) of these individual clusters through X-ray spectral fits and then estimate their gravitational masses (A1095=2.7-0.3+0.3, A1095E=2.3-0.6+0.3, A1926a=1.3-0.2+0.2, A1926b=1.1-0.4+0.81014M⊙)). We also show a rich set of substructures, including large position offsets between the diffuse X-ray centroids and the brightest galaxies of the clusters, which suggests that they are dynamically young. Incorporating SDSS and NVSS/FIRST data, we further examine the large-scale structure environment and radio emission of the clusters to probe their origins, which also leads to the discovery of two additional X-ray-emitting clusters in the A1926 field. The members themselves of cluster pairs are probably the results of recent subcluster mergers or still in early formation stages, consistent with the hierarchical formation paradigm of galaxy clusters.