Radio observations of the 13hXMM-Newton/ROSAT Deep X-ray Survey Area

In order to determine the relationship between the faint X-ray and faint radio source populations, and hence to help understand the X-ray and radio emission mechanisms in those faint source populations, we have made a deep 1.4-GHz Very Large Array radio survey of the 13^h+ 38°XMM-Newton/ROSAT X-ray Survey Area. From a combined data set of 10-h, B-configuration data and 14-h, A-configuration data, maps with 3.35-arcsec resolution and a noise limit of 7.5 μJy were constructed. A complete sample of 449 sources was detected within a 30-arcmin diameter region above a 4σ detection limit of 30 μJy, at the map centre, making this one of the deepest radio surveys at this frequency. The differential source count shows a significant upturn at submilliJansky flux densities, similar to that seen in other deep surveys at 1.4 GHz (e.g. the Phoenix survey), but larger than that seen in the Hubble Deep Field (HDF) which may have been selected to be underdense. This upturn is well modelled by the emergence of a population of medium-redshift star-forming galaxies which dominate at faint flux densities. The brighter source counts are well modelled by active galactic nuclei.