Astrophys. J., Suppl. Ser., 165, 19-56 (2006/July-0)
The serendipitous extragalactic X-ray source identification (SEXSI) program. III. Optical spectroscopy.
ECKART M.E., STERN D., HELFAND D.J., HARRISON F.A., MAO P.H. and YOST S.A.
Abstract (from CDS):
We present the catalog of 477 spectra from the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program, a survey designed to probe the dominant contributors to the 2-10 keV cosmic X-ray background. Our survey covers 1 deg2 of sky to 2-10 keV fluxes of 1x10–14 ergs/cm2/s, and 2 deg2 for fluxes of 3x10–14 ergs/cm2/s. Our spectra reach to R-band magnitudes of ≲24 and have produced identifications and redshifts for 438 hard X-ray sources. Typical completeness levels in the 27 Chandra fields studied are 40%-70%. The vast majority of the 2-10 keV selected sample are active galactic nuclei (AGNs) with redshifts between 0.1 and 3; our highest redshift source lies at z=4.33. We find that few sources at z<1 have high X-ray luminosities, reflecting a dearth of high-mass, high-accretion-rate sources at low redshift, a result consistent with other recent wide-area surveys. We find that half of our sources show significant obscuration, with NH>1022/cm2, independent of unobscured luminosity. We classify 168 sources as emission-line galaxies; all are X-ray-luminous (LX>1041 ergs/s) objects with optical spectra lacking both high-ionization lines and evidence of a nonstellar continuum. The redshift distribution of these emission-line galaxies peaks at a significantly lower redshift than does that of the sources we spectroscopically identify as AGNs. We conclude that few of these sources, even at the low-luminosity end, can be powered by starburst activity. Stacking spectra for a subset of these sources in a similar redshift range, we detect [Ne V] λ3426 emission, a clear signature of AGN activity, confirming that the majority of these objects are Seyfert 2 galaxies in which the high-ionization lines are diluted by stellar emission. We find a total of 33 objects lacking broad lines in their optical spectra that have quasar X-ray luminosities (LX>1044 ergs/s), the largest sample of such objects identified to date. In addition, we explore 17 AGNs associated with galaxy clusters and find that the cluster-member AGN sample has a lower fraction of broad-line AGNs than does the background sample.
Catalogs - Galaxies: Active - Surveys - X-Rays: Diffuse Background - X-Rays: Galaxies - X-Rays: Galaxies: Clusters - X-Rays: General
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<Available at CDS (J/ApJS/165/19): table2.dat notes.dat>
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