A large, uniform sample of X-ray emitting AGN: selection approach and an initial catalog from the ROSAT All-Sky and Sloan Digital Sky Surveys
Date
2003-11Author
Anderson, Scott
Voges, Wolfgang
Margon, Bruce
Trumper, Joachim
Agueros, Marcel
Boller, Thomas
Collinge, Matthew
Homer, Lee
Stinson, Gregory
Strauss, Michael
Annis, James
Gomez, Percy
Hall, Patrick
Nichol, Robert
Richards, Gordon
Schneider, Donald
Vanden Berk, Daniel
Fan, Xiaohui
Ivezic, Zeljko
Munn, Jeffrey
Newberg, Heidi Jo
Richmond, Michael
Weinberg, David
Yanny, Brian
Bahcall, Neta
Brinkmann, Jonathan
Fukugita, Masataka
York, Donald
Metadata
Show full item recordAbstract
Many open questions 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 when 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 follow-up from the Sloan Digital Sky Survey (SDSS); these two surveys
prove to be serendipitously very well matched in sensitivity. As part of the SDSS
software pipelines, optical objects in the SDSS photometric catalogs are automatically
positionally cross-correlated with RASS X-ray sources. Then priorities for follow-on
SDSS optical spectra of candidate counterparts are automatically assigned using an
algorithm based on the known ratios of fx/fopt for various classes of X-ray emitters
at typical RASS fluxes of 10−13 erg cm−2 s−1. SDSS photometric parameters for
optical morphology, magnitude, colors, plus FIRST radio information, serve as proxies
for object class.
Initial application of this approach to RASS/SDSS data from 1400 deg2 of sky
provides a catalog of more than 1200 spectroscopically confirmed quasars and other
AGN that are probable RASS identifications. Most of these are new identifications,
and only a few percent of the AGN counterparts are likely to be random superpositions.
The magnitude and redshift ranges of the counterparts are very broad, extending over
15 < m < 21 and 0.03 < z < 3.6, respectively. Although most identifications are
quasars and Seyfert 1s, a variety of other AGN subclasses are also sampled. Substantial
numbers of rare AGN types are found, including more than 130 narrow-line Seyfert 1s
and 45 BL Lac candidates. These early results already provide a very sizeable
set of source identifications, demonstrate utility of the sample in multi-waveband
investigations, and show the capability of the joint RASS/SDSS approach to efficiently
proceed towards the largest homogeneously selected/observed sample of X-ray emitting
quasars and other kinds of AGN.