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D.J. Helfand, I. A. Yadigaroglu, R. Berger (Columbia University), M. Postman, R.L. White (STScI), T. R. Lauer (NOAO), W. R. Oegerle (JHU), R.H. Becker (UC Davis and IGPP/LLNL)
We have used the deep I-band survey of Postman et al. to search for optical counterparts to radio sources from the VLA FIRST survey. A total of 1131 FIRST sources fall within the ~16 deg2 of the optical survey which extends to I~24. The optical astrometry has been calibrated using the FIRST (VLA B configuration) radio positions supplemented by a catalog of sources from A-configuration observations covering a portion of the field; after removal of optical reference frame distortions, CCD frame-to-frame shifts, and intraframe distortions, the absolute astrometric accuracy is better than ~0.3" throughout the survey region. We report here the identification of ~700 radio sources with flux densities ranging from 1 to 750 mJy; fewer than 30 of these sources have been previously identified. We discuss the detected fraction of radio sources as a function of optical magnitude, radio flux, and radio and optical morphology. Spectroscopic identifications have been obtained for a significant fraction of the stellar counterparts; most, as expected, are quasars. We also discuss the galaxy surface density in the vicinity of the radio sources, and comment on the utility of the radio survey in selecting high-redshift galaxy clusters and in exploring larger scale structures.
This work is supported at Columbia University by grants from NASA and the NSF.