AGN in deep radio/X-ray surveys: Hunting the earliest massive galaxies

Abstract

Despite the plethora of deep (sub-mJy) radio surveys there remains considerable doubt as to the exact nature of the galaxies contributing to the source counts. Current evidence suggests that star formation in moderately luminous normal galaxies is responsible for the bulk of the emission below 1 mJy. However given the sensitivities of these surveys we would expect a fraction of these sources to be distant radio galaxies. Using deep VLA and GMRT data we have found ~20 high-z candidate radio galaxies in two fields using the classical ultra-steep radio spectrum technique (De Breuck et al. 2000) and selecting galaxies with faint (i’ > 25) optical counterparts. Several of these sources have X-ray detections in our deep XMM/Chandra observations and have fluxes high enough to put them in the quasar regime if they lie above redshift 3. Recently performed Spitzer GTO observations and upcoming near-infrared observations will help reveal the nature of these sources.