Session 63 - Surveys of Galaxies.
Oral session, Thursday, January 08
Georgetown,

## [63.03] Using Deep Radio and Optical Surveys to find z > 6 Candidates

E. A. Richards (U. Virginia), R. A. Windhorst (Arizona State U.), K. I. Kellermann, E. B. Fomalont (NRAO), R. B. Partridge (Haverford College)

We have recently completed several deep surveys using the VLA at 8 GHz with one sigma sensitivities ranging from 1.5 \muJy to 5 \muJy. These surveys are capable of detecting radio galaxies with luminsoity in excess of the break in the RLF, P_* \sim 10^25 W/Hz, out to z = 10 if they exist and thus are well suited for studying AGN formation and evolution. Follow-up optical work has identified more than 90% of these microjy radio sources, primarily with luminous star-forming galaxies and low-luminosity AGN (--23 < M_B<--21). Suprisingly, these microjy radio sources have approximately the same median redshift (z \sim 0.8) as the 3C identifications, although that sample reached almost one million times less sensitive flux denisty limits.

A few radio sources remain unidentified down to the best optical limits available. In particular, one radio source located in the HDF has no optical counterpart to the detection limit of R \sim 29. We discuss the possibility that this source is a very young AGN, possibly at z > 6, and thus obscured by the Lyman break at optical wavelengths. If our hypothesis is corect, then the host should be detectable in a reasonable integration with NICMOS.