Sloan Digital Sky Survey Active Galactic Nuclei with X-Ray Emission fromROSATPSPC Pointed Observations

Abstract

We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) spectroscopic catalog with X-ray counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the catalog of radio sources from the Faint Images of the Radio Sky at Twenty cm survey, 224 turned up in our sample of SDSS X-ray AGNs. The sample objects are given in a catalog that contains optical and X-ray parameters and supporting data, including redshifts; it also contains radio emission parameters where available. We illustrate the content of our catalog and its potential for AGN science by providing statistical relationships for the catalog data. The potential of the morphological information is emphasized by confronting the statistics of optically resolved, mostly low-redshift AGNs with unresolved AGNs that occupy a much wider redshift range. The immediate properties of the catalog objects include significant correlation of X-ray and optical fluxes, which is consistent with expectations. Also expected is the decrease of X-ray flux toward higher redshifts. The X-ray-to-optical flux ratio for the unresolved AGNs exhibits a decline toward higher redshifts, in agreement with previous results. The resolved AGNs, however, display the opposite trend. The X-ray hardness ratio shows a downward trend with increasing low-energy X-ray flux and no obvious dependence on redshift. At a given optical brightness, X-ray fluxes of radio-loud AGNs are, on average, higher than those of radio-quiet AGNs by a factor of 2. We caution, however, that because of the variety of selection effects present in both the WGACAT and the SDSS, the interpretation of any relationships based on our sample of X-ray AGNs requires a careful analysis of these effects.