Other
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21333906k&link_type=abstract
American Astronomical Society, AAS Meeting #213, #339.06; Bulletin of the American Astronomical Society, Vol. 41, p.402
Other
Scientific paper
Previous surveys of faint radio sources made with the VLA, Westerbork, and the Australia Telescope have shown the well known increase in source density at flux densities below one millijansky, but the mix between AGN and star formation remains uncertain. We report on VLA observations of the Chandra Deep Field South at 6 and 20 cm and the Extended Chandra Deep Field South at 20 cm which are complemented by sensitive Chandra X-ray observations, and unusually complete optical identifications based on a broad range of optical material. We have found optical counterparts for 95% of the cataloged radio sources of which 74% have spectroscopic or photometric redshifts down to our I and R mag 26 limit.
Analysis of the multi-band data suggests a significant population of millijansky AGN that have been missed by other surveys with brighter optical magnitude limits. However, we found no single radio, optical, or X-ray property that can always be used to unambiguously discriminate between AGN and star formation. About half of the microjansky AGN appear to represent a separate population which is distinct from the radio loud AGN population, and are not merely the low end of a continuous luminosity function. Although most of the AGN are found in E type galaxies, as is the case for the more powerful quasars and AGN, we find that approximately 20% of the AGN in the VLA catalogue, which are characterized by high X-ray luminosity, are located in Spiral or Irregular type galaxies. High observed values of radio to optical luminosity, which are generally representative of AGN rather than star formation, are thought to be the result of the large radio luminosity rather than to optical obscuration.
CDF-S Team
Fomalont Edward B.
Kellermann Kenneth I.
Mainieri Vincenzo
Miller Natalia
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