VIRMOS 0.6GHz J022702-045159A , the SIMBAD biblio

We present the low frequency (610MHz) radio source counts of the VVDS-VLA field and investigate the radio spectral index properties of the sub-mJy population. We use new deep (rms≃50µJy/beam) observations of the VVDS-VLA field obtained at 610MHz with the GMRT and matched in resolution (6-arcsec) with already available VLA data at 1.4GHz on the same field. We find evidence of a change of the dominant population of radio sources below 0.5mJy (at 1.4GHz): between 0.15 and 0.5mJy the median spectral index is significantly flatter (α=-0.46±0.03) than that of brighter sources (α=-0.67±0.05). A relevant contribution below 0.5mJy from a population of flat spectrum low luminosity compact AGNs and radio quiet QSOs could explain this effect. At even fainter flux density, between 0.10 and 0.15mJy at 1.4GHz, the median spectral index steepens again (α=-0.61±0.04) suggesting that the contribution of starburst galaxies becomes important below ∼0.2mJy. Finally we present a sample of 58 candidate ultra-steep sources with radio flux density from one to two orders of magnitude lower than any other sample of such objects.