Letter to the Editor

Herschel-ATLAS: Extragalactic number counts from 250 to 500 microns^*

¹ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK e-mail: d.clements@imperial.ac.uk
² School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
³ SSTD, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
⁴ Institute for Space Imaging Science University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada
⁵ Dept. of Physics & Astronomy, University of California, Irvine, CA 92697, USA
⁶ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK
⁷ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
⁸ Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille France
⁹ University of Padova, Department of Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
¹⁰ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38200 La Laguna, Spain
¹¹ National Radio Astronomy Observatory, PO Box 2, Green Bank, WV 24944, USA
¹² Astrophysics Science Division, Observational Cosmology Laboratory, Code 665, Goddard Space Flight Center, Greenbelt MD 20771, USA
¹³ Instituto de Física de Cantabria (CSIC-UC), Santander, 39005, Spain
¹⁴ UK Astronomy Technology Center, Royal Observatory Edinburgh, Edinburgh, EH9 3HJ, UK
¹⁵ Centre for Astrophysics Research, Science and Technology Research Centre, University of Hertfordshire, Herts AL10 9AB, UK
¹⁶ Institut d'Astrophysique Spatiale (IAS), Batiment 121, 91405 Orsay, France; and Université Paris-Sud 11 and CNRS (UMR 8617), France
¹⁷ Astrophysics Branch, NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035, USA
¹⁸ Dept. of Physics and Astronomy, The Open University, Milton Keynes, MK7 6AA, UK
¹⁹ Scuola Internazionale Superiore di Studi Avanzati, via Beirut 2-4, 34151 Triest, Italy
²⁰ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, B.C., V6T 1Z1, Canada
²¹ Herschel Science Centre, ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
²² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²³ Oxford Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford, OX1 3RH, UK

Received: 3 March 2010
Accepted: 12 May 2010

Abstract

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 μm when completed, reaching flux limits (5σ) from 32 to 145 mJy. We here present galaxy number counts obtained for SPIRE observations of the first ~14 sq. deg. observed at 250, 350 and 500 μm.

Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts.

Results. We find a steep rise in the number counts at flux levels of 100–200 mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.