IAU01796
Presentation type requested: ORAL
THE ATESP 5GHZ SURVEY: PROBING THE SUB-MJY POPULATION
Isabella Prandoni
Institute of Radioastronomy of the CNR
We used the ATCA to follow-up at 5GHz the region previously covered by the sub-mJy ATESP 1.4GHz survey. In particular we imaged a 1sq.degr. area where, in addition to the 1.4 GHz information, extensive UBVRI deep (I<26) optical imaging and spectroscopy are becoming available. The 5GHz survey has produced a catalogue of 111 radio sources complete down to S(5GHz)~0.4 mJy (6 sigma). The derived 5GHz source counts are consistent with others reported in the literature, and provide the best source counts' determination available today in the flux range 0.4-2 mJy. The 1.4 and 5 GHz information allowed us to study the radio spectral properties of the ATESP radio sources. We found a significant flattening of the 1.4-5 GHz spectral index going to fainter fluxes: the fraction of sources with flat/inverted spectra increases from 30% at S(1.4GHz)>2 mJy up to 60% at S(1.4GHz<2 mJy. We then used the radio and optical information available to assess the nature of the ATESP sub-mJy sources and the physical processes responsible for such a flattening. Preliminary results indicate that flat/inverted sources are more probably triggered by nuclear activity than by star formation.
Parma Paola , Wieringa Mark H, Loretta Gregorini , de Ruiter Hans R, Vettolani Gianpaolo , Ekers Ron D
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