{
  "id": "1606.09254",
  "version": "v1",
  "published": "2016-06-29T20:00:04.000Z",
  "updated": "2016-06-29T20:00:04.000Z",
  "title": "The Herschel-ATLAS Data Release 1 Paper II: Multi-wavelength counterparts to submillimetre sources",
  "authors": [
    "N. Bourne",
    "L. Dunne",
    "S. J. Maddox",
    "S. Dye",
    "C. Furlanetto",
    "C. Hoyos",
    "D. J. B. Smith",
    "S. Eales",
    "M. W. L. Smith",
    "E. Valiante",
    "M. Alpaslan",
    "E. Andrae",
    "I. K. Baldry",
    "M. E. Cluver",
    "A. Cooray",
    "S. P. Driver",
    "J. S. Dunlop",
    "M. W. Grootes",
    "R. J. Ivison",
    "T. H. Jarrett",
    "J. Liske",
    "B. F. Madore",
    "C. C. Popescu",
    "A. G. Robotham",
    "K. Rowlands",
    "M. Seibert",
    "M. A. Thompson",
    "R. J. Tuffs",
    "S. Viaene",
    "A. H. Wright"
  ],
  "comment": "Resubmitted to MNRAS after first referee report",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO",
    "astro-ph.SR"
  ],
  "abstract": "This paper is the second in a pair of articles presenting data release 1 (DR1) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), the largest single open-time key project carried out with the Herschel Space Observatory. The H-ATLAS is a wide-area imaging survey carried out in five photometric bands at 100, 160, 250, 350 and 500$\\mu$m covering a total area of 600deg$^2$. In this paper we describe the identification of optical counterparts to submillimetre sources in DR1, comprising an area of 161 deg$^2$ over three equatorial fields of roughly 12$^\\circ$x4.5$^\\circ$ centred at 9$^h$, 12$^h$ and 14.5$^h$ respectively. Of all the H-ATLAS fields, the equatorial regions benefit from the greatest overlap with current multi-wavelength surveys spanning ultraviolet (UV) to mid-infrared regimes, as well as extensive spectroscopic coverage. We use a likelihood-ratio technique to identify SDSS counterparts at r<22.4 for 250-$\\mu$m-selected sources detected at $\\geq$ 4$\\sigma$ ($\\approx$28mJy). We find `reliable' counterparts (reliability R$\\geq$0.8) for 44,835 sources (39 per cent), with an estimated completeness of 73.0 per cent and contamination rate of 4.7 per cent. Using redshifts and multi-wavelength photometry from GAMA and other public catalogues, we show that H-ATLAS-selected galaxies at $z<0.5$ span a wide range of optical colours, total infrared (IR) luminosities, and IR/UV ratios, with no strong disposition towards mid-IR-classified AGN in comparison with optical selection. The data described herein, together with all maps and catalogues described in the companion paper (Valiante et al. 2016), are available from the H-ATLAS website at www.h-atlas.org.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-06-29T20:00:04.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "submillimetre sources",
      "herschel-atlas data",
      "multi-wavelength counterparts",
      "multi-wavelength surveys spanning ultraviolet",
      "astrophysical terahertz large area survey"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}