A Near-IR Survey of the SWIRE/ELAIS-S1 Field with SofI. I: The Source Catalogue

We present a medium deep near-IR imaging follow-up of the SWIRE survey on the central ˜ 0.82 square degrees of the ELAIS-S1 field. We observed this region with SofI at the NTT in the J and K_s bands in 4 different periods, during 2002 and 2003. The combination of wide area and medium sensitivity allow us to detect evolved ellipticals, young disk galaxies, starbursts Seyferts and obscured quasars. The extensive multiwavelength follow-up in the field allows us to constrain the evolution and contribution of these sources to the cosmic infrared background. Near-IR observations of the ELAIS-S1 field are essential to complete the picture of the spectral energy distributions for the sources in our field. We aim to build up detailed SEDs for a large sample of sources using the combination of all multiwavelength observations. The near-infrared band is essential for categorizing, for example, Extremely Red Galaxies (EROs) and Distant Red Galaxies (DRGs). J- and K_s-band catalogues of sources have been produced by using both J- and K_s-band selection. Our catalogue is complete to 95% at J = 19.82 and K_s = 18.73 (Vega) to the ˜ 7500 sources secure catalogue. DRGs and EROs within the catalogue have also been identified. Source counts in the K_s-band survey agree well with previous shallower surveys and have a break at about K_s ˜ 16 to the ˜ 7500 sources secure catalogue. A similar break is seen in the J-band survey at J˜ 17.5. Details of the work presented here will be published in Dias et al. 2007