The VIRMOS RADIO survey

People involved: Ciliegi, de Ruiter, Zamorani.

The radio survey has been obtained with the VLA at 1.415 GHz in one of the VIRMOS region where deep $BVRI$ band photometry was already available (from CFHT observations) to a limiting magnitude ($5\sigma$) of about 25.5 and, for a fraction of the area, in the $U$ and $K$ bands with the ESO telescopes to a limiting magnitude of 25 and 20 respectively. The VIRMOS VLA radio survey has mapped an area of 1 square degree with a uniform noise of $\sim85\:\mu$Jy ($5\sigma$). A catalogue of radio sources brighter than the local $5\sigma$ threshold has been extracted from the 1 degree radio map. It contains 1054 radio sources, 19 of which are considered as multiple, i.e. fitted with at least two separate components. The source counts of this radio catalogue are in very good agreement with those of other surveys. In particular, our point at the faintest flux level ($\sim 0.1$ mJy) is fully consistent (with more robust statistics thanks to the higher number of sources and a large area covered) with the points obtained with a very deep radio observation in the Hubble Deep Field (HDF). A detailed description of the VIRMOS RADIO survey is reported in the paper Bondi, Ciliegi, Zamorani et al. 2003.

Subsequently, using the already available optical data, we performed a detailed optical identification using a Likelihood Ratio Analysis. We found $\sim730$ reliable optical counterparts. The expected number of spurious identifications is $\sim 40$ leading to an identification percentage of $\sim70$%.

The colour properties of the optical counterparts of the radio sources have been analysed using the $(B-V)$ and $(V-I)$ colours. The optical counterparts of the radio sources classified as extended have been analysed in three different magnitude slices. While in the brightest magnitude range ($18<I_{AB}<20$) the optical colour properties of the radio sources are not different from those of the whole optical sample, at fainter magnitudes the median colour of the radio sources is redder than the median colour of the whole optical sample, probably indicating a higher redshift for the radio sources.