HerMES: deep number counts at 250 μm, 350 μm and 500 μm in the COSMOS and GOODS-N fields and the build-up of the cosmic infrared background

¹ Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu – CNRS – Université Paris Diderot, CE-Saclay, pt courrier 131, 91191 Gif-sur-Yvette, France
e-mail: matthieu.bethermin@cea.fr
² Institut d’Astrophysique Spatiale (IAS), bâtiment 121, Université Paris-Sud 11 and CNRS (UMR 8617), 91405 Orsay, France
³ Laboratoire d’Astrophysique de Marseille, OAMP, Université Aix-Marseille, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁴ Center for Astrophysics and Space Astronomy 389-UCB, University of Colorado, Boulder, CO 80309, USA
⁵ NASA, Ames Research Center, Moffett Field, CA 94035, USA
⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
⁸ California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁹ Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁰ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
¹¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
¹² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
¹³ Departamento de Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁴ Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
¹⁵ Dept. of Physics & Astronomy, University of California, Irvine, CA 92697, USA
¹⁶ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁷ Astronomy Centre, Dept. of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
¹⁸ Dipartimento di Astronomia, Università di Padova, vicolo Osservatorio, 3, 35122 Padova, Italy
¹⁹ Dept. of Astrophysical and Planetary Sciences, CASA 389-UCB, University of Colorado, Boulder, CO 80309, USA
²⁰ ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
²¹ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
²² Hubble Fellow  
²³ National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
²⁴ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
²⁵ Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 6, 98bis boulevard Arago, 75014 Paris, France
²⁶ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
²⁷ RAL Space, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
²⁸ Institute for Space Imaging Science, University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada
²⁹ Department of Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford OX1 3RH, UK
³⁰ Max Planck Institut für Plasma Physik and Excellence Cluster, 85748 Garching, Germany
³¹ Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, JPL, Pasadena, CA 91125, USA
³² CSIRO Astronomy & Space Science, PO Box 76, Epping, NSW 1710, Australia
³³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³⁴ Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, 28691 Madrid, Spain
³⁵ Astrophysics Group, Physics Department, University of the Western Cape, Private Bag X17, 7535 Bellville, Cape Town, South Africa

Received: 21 December 2011
Accepted: 9 March 2012

Abstract

Aims. The Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel space telescope has provided confusion limited maps of deep fields at 250 μm, 350 μm, and 500 μm, as part of the Herschel Multi-tiered Extragalactic Survey (HerMES). Unfortunately, due to confusion, only a small fraction of the cosmic infrared background (CIB) can be resolved into individually-detected sources. Our goal is to produce deep galaxy number counts and redshift distributions below the confusion limit at SPIRE wavelengths (~20 mJy), which we then use to place strong constraints on the origins of the cosmic infrared background and on models of galaxy evolution.

Methods. We individually extracted the bright SPIRE sources (>20 mJy) in the COSMOS field with a method using the positions, the flux densities, and the redshifts of the 24 μm sources as a prior, and derived the number counts and redshift distributions of the bright SPIRE sources. For fainter SPIRE sources (<20 mJy), we reconstructed the number counts and the redshift distribution below the confusion limit using the deep 24 μm catalogs associated with photometric redshift and information provided by the stacking of these sources into the deep SPIRE maps of the GOODS-N and COSMOS fields. Finally, by integrating all these counts, we studied the contribution of the galaxies to the CIB as a function of their flux density and redshift.

Results. Through stacking, we managed to reconstruct the source counts per redshift slice down to  ~2 mJy in the three SPIRE bands, which lies about a factor 10 below the 5σ confusion limit. Our measurements place tight constraints on source population models. None of the pre-existing models are able to reproduce our results at better than 3-σ. Finally, we extrapolate our counts to zero flux density in order to derive an estimate of the total contribution of galaxies to the CIB, finding 10.1_-2.3^+2.6 nW m^-2 sr^-1, 6.5_-1.6^+1.7 nW m^-2 sr^-1, and 2.8_-0.8^+0.9 nW m^-2 sr^-1 at 250 μm, 350 μm, and 500 μm, respectively. These values agree well with FIRAS absolute measurements, suggesting our number counts and their extrapolation are sufficient to explain the CIB. We find that half of the CIB is emitted at z = 1.04, 1.20, and 1.25, respectively. Finally, combining our results with other works, we estimate the energy budget contained in the CIB between 8 μm and 1000 μm: 26_-3⁺⁷ nW m^-2 sr^-1.