Magellan Spectroscopy of AGN Candidates in the COSMOS Field

We present spectroscopic redshifts for the first 466 X-ray- and radio-selected AGN targets in the 2 deg<SUP>2</SUP> COSMOS field. Spectra were obtained with the IMACS instrument on the Magellan (Baade) telescope, using the nod-and-shuffle technique. We identify a variety of type 1 and type 2 AGNs, as well as red galaxies with no emission lines. Our redshift yield is 72% down to i<SUB>AB</SUB>=24, although the yield is >90% for i<SUB>AB</SUB><22. We expect the completeness to increase as the survey continues. When our survey is complete and additional redshifts from the zCOSMOS project are included, we anticipate ~1100 AGNs with redshifts over the entire COSMOS field. Our redshift survey is consistent with an obscured AGN population that peaks at z~0.7, although further work is necessary to disentangle the selection effects. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 and based on data collected at the Magellan Telescope, which is operated by the Carnegie Observatories.