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Session 14 - Surveys.
Display session, Monday, January 13
Metropolitan Ballroom,

[14.04] Optical Identification of 50,000 Radio Sources

D. J. Helfand (Columbia), R. H. Becker (UC Davis), R. L. White (STScI), R. G. McMahon (Cambridge)

Three years ago, we began a project to produce Faint Images of the Radio Sky at Twenty-cm that is creating the centimetric equivalent of the Palomar Observatory Sky Survey. Using the NRAO VLA in its B-configuration, we are obtaining uniform coverage over 10,000 deg^2 of the North Galactic Cap to a flux density limit of 1.0 mJy; every source down to the survey threshold has a position accurate to better than 1^\prime\prime. This level of astrometric precision is essential in obtaining optical idensitifications for a significant fraction of the one million radio sources that will be detected in the survey, since the median optical magnitude for a FIRST counterpart is \sim 23. We have used the Automated Photographic Measurement (APM) scans of the POSS-I plates to begin the optical identification program for FIRST. To the limiting magnitude of the red POSS I plate (E=20.0) we find that \sim 20% of the sources have optical counterparts. Source populations represented include nearby stars, star-forming galaxies, radio galaxies and quasars. The color and morphological information contained in the APM catalog for each counterpart allow us to select large samples of various source types for followup observations (see Blanton et al. and Gregg et al. at this meeting for examples). Prior to this work, fewer than 300 optical identifications for radio-selected objects in the 1--30 mJy range had been obtained. We present here a statistical analysis of 50,000 such optical identifications from the first 3000 deg^2 of the survey. The FIRST project is supported by grants from the National Geographic Society, the National Science Foundation, NATO, IGPP, Columbia University, and Sun Microsystems.

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