Bright extragalactic x-ray sources with optical and radio counterparts

This thesis characterizes a key constituent of the soft X-ray ROSAT All Sky Survey Bright Source Catalogue (RBSC), namely active galaxies, by cross-identifying it with the N.R.A.O. VLA Sky Survey (NVSS) radio source catalogue and the United States Naval Observatory A2.0 optical catalogue. We developed a new reliability technique for linking X-ray objects to optical counterparts using the radio positions, which are more accurate than the X-ray positions. Applying this technique, we identified 1556 objects above the 0.1 counts s−1 completeness limit of the RBSC with Galactic latitudes |b| > 15° and J2000 declinations δ > −40°.; We compared and contrasted this sample with the entire RBSC to understand the nature of X-ray-selected AGN. We detected nearly all radio-loud extragalactic X-ray objects and found that radio-loud quasars are intrinsically more luminous sources than radio-quiet quasars in all but the optical waveband. We confirm results from the Bright Quasar Survey (Laor 2000) that radio luminosity and black-hole mass are roughly proportional for radio-quiet objects and for radio-loud objects, but with different constants of proportionality. There appears to be a transition black hole mass of approximately 108.5 $M\odot$ below which objects lower than this value are radio-quiet, and above which they are radio-loud. We find that objects in our sample support a unification scheme based on (1) orientation, (2) black hole mass and (3) accretion rate. Since we do not have optical morphological information, we are unable to conclusively confirm the possibility that merger history might also play a significant role.; For a complete subset of objects, we calculated the local X-ray, radio and optical luminosity functions for individual class types (e.g. Seyferts, Broad and Narrow Line Radio Galaxies, Quasars, BL Lacs, clusters of galaxies). We extended the X-ray luminosity function down to 1040 ergs s−1 for some classes. In doing so, we discovered a strong break in the luminosity distribution at 1041.5 ergs s −1. This break corresponds to a transition from Seyfert 2 to Seyfert 1 and probably represents the typical amount of scattering X-ray radiation present in an obscured AGN. We confirm that Seyfert 1 galaxies produce the bulk of the X-ray emission in the local Universe.