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2002ApJS..143....1McMahon+
Optical Counterparts for 70,000 Radio Sources: APM Identifications for
the FIRST Radio Survey
*Authors:*
McMahon, Richard G.
White, Richard L.
Helfand, David J.
Becker, Robert H.
*Affiliation:*
AA(University of Cambridge, Institute of Astronomy, Madingley Road,
Cambridge CB3 0HA, England; rgm@ast.cam.ac.uk), AB(Space Telescope
Science Institute, 3700 San Martin Drive, Baltimore, MD 21218;
rlw@stsci.edu), AC(Astronomy Department, Columbia University, New York,
NY 10027; djh@astro.columbia.edu), AD(Physics Department, University of
California, Davis, CA 95616; and IGPP/Lawrence Livermore National
Laboratory; bob@igpp.ucllnl.org)
*Journal:*
The Astrophysical Journal Supplement Series, Volume 143, Issue 1, pp.
1-23.
*Publication Date:*
11/2002
*Bibliographic Code:*
2002ApJS..143....1M
Abstract
We describe a program to identify optical counterparts to radio sources
from the VLA FIRST survey using the Cambridge APM scans of the POSS-I
plates. We use radio observations covering 4150 deg^2 of the north
Galactic cap to a 20 cm flux density threshold of 1.0 mJy; the 382,892
sources detected all have positional uncertainties of <1" (radius of 90%
confidence). Our description of the APM catalog, derived from the 148
POSS-I O and E plates covering this region, includes an assessment of
its astrometric and photometric accuracy, a photometric recalibration
using the Minnesota APS catalog, a discussion of the classification
algorithm, and quantitative tests of the catalog's reliability and
completeness. We go on to show how the use of FIRST sources as
astrometric standards allows us to improve the absolute astrometry of
the POSS plates by nearly an order of magnitude to ~0.15" rms. Matching
the radio and optical catalogs yields counterparts for over 70,000 radio
sources; we include detailed discussions of the reliability and
completeness of these identifications as a function of optical and radio
morphology, optical magnitude and color, and radio flux density. An
analysis of the problem of radio sources with complex morphologies
(e.g., double-lobed radio galaxies) is included. We conclude with a
brief discussion of the source classes represented among the radio
sources with identified counterparts.