ATLAS - I. Third Release of 1.4 GHz Mosaics and Component Catalogues

We present the third data release from the Australia Telescope Large Area Survey (ATLAS). These data combine the observations at 1.4 GHz before and after upgrades to the Australia Telescope Compact Array reaching a sensitivity of 14 microJy/beam in 3.6 deg^2 over the Chandra Deep Field South (CDFS) and of 17 microJy/beam in 2.7 deg^2 over the European Large Area ISO Survey South 1 (ELAIS-S1). We used a variety of array configurations to maximise the uv coverage resulting in a resolution of 16 by 7 arcsec in CDFS and of 12 by 8 arcsec in ELAIS-S1. After correcting for peak bias and bandwidth smearing, we find a total of 3034 radio source components above 5 sigma in CDFS, of which 514 (17 per cent) are considered to be extended. The number of components detected above 5 sigma in ELAIS-S1 is 2084, of which 392 (19 per cent) are classified as extended. The catalogues include reliable spectral indices (delta alpha < 0.2) between 1.40 and 1.71 GHz for ~350 of the brightest components.