A Very Large, Uniform Sample of X-ray Emitting AGN: Selection Approach and Initial Catalog from ROSAT and SDSS
Abstract
Many problems in X-ray astronomy are limited by the relatively small number of objects in uniform optically-identified and observed samples, especially when rare subclasses are considered, or subsets are isolated to search for evolution or correlations between wavebands. We describe initial results of a new program aimed to ultimately yield ~104 fully characterized X-ray source identifications---a sample about an order of magnitude larger than earlier efforts. The technique is detailed, and employs X-ray data from the ROSAT All Sky Survey (RASS), and optical imaging and spectroscopic followup from the Sloan Digital Sky Survey (SDSS); these two surveys prove to be serendipitously very-well matched in sensitivity. Optical objects in the SDSS photometric catalogs are positionally cross-correlated with RASS X-ray sources. Priorities for follow-on SDSS optical spectra of candidate counterparts are automatically assigned, using an algorithm based on the known ratios of fx}/f{opt for various classes of X-ray emitters at typical RASS flux limits, and with SDSS photometric parameters for optical morphology, magnitude, colors, plus FIRST radio information, serving as proxies for object class. Early SDSS data from 1400 deg2 of sky already provide a catalog of 1200 spectroscopically confirmed quasars and other AGN that are probable RASS identifications. The magnitude and redshift range of the counterparts is very broad, extending over 15<m<21 and 0.02<z<4.9. A wide range of AGN subclasses are sampled, especially QSOs and Seyferts of various kinds, but also, e.g., including several dozen BL Lac candidates. These early results already provide a very sizeable set of identifications, and demonstrate the capability of the joint RASS/SDSS approach to efficiently proceed towards the largest homogeneously selected/observed sample of X-ray emitting quasars and related AGN.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AAS...201.1120A