2009ApJ...694..235P

We present a detailed analysis of 256 radio sources from our deep (flux density limit of 42 µJy at the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey. The radio population is studied by using a wealth of multiwavelength information in the radio, optical, and X-ray bands. The availability of redshifts for ∼80% of the sources in our complete sample allows us to derive reliable luminosity estimates for the majority of the objects. X-ray data, including upper limits, for all our sources turn out to be a key factor in establishing the nature of faint radio sources. Due to the faint optical levels probed by this study, we have uncovered a population of distant active galactic nuclei (AGNs) systematically missing from many previous studies of sub-millijansky radio source identifications. We find that, while the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGNs make up an approximately equal fraction of the sub-millijansky sky, contrary to some previous results. The AGNs include radio galaxies, mostly of the low-power, Fanaroff-Riley I type, and a significant radio-quiet component, which amounts to approximately one fifth of the total sample. The ratio of radio-to-optical luminosity depends more on radio luminosity, rather than being due to optical absorption.