GOODS-Herschel: identification of the individual galaxies responsible for the 80–290 μm cosmic infrared background

¹ Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu – CNRS – Université Paris Diderot, CEA-Saclay, pt courrier 131, 91191 Gif-sur-Yvette, France
e-mail: roger.leiton@cea.fr
² Astronomy Department, Universidad de Concepción, Concepción, Chile
e-mail: roger.leiton@astro-udec.cl
³ School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, 130-722 Seoul, Republic of Korea
⁴ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁵ Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
⁶ Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, 28691 Madrid, Spain
⁷ National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁹ Department of Physics, University of Crete, 71003 Heraklion, Greece
¹⁰ Institute for Astronomy, National Observatory of Athens, 15236 Penteli, Greece
¹¹ Univ. Paris Sud, Institut d’Astrophysique Spatiale (UMR 8617), Bât. 121, 91405 Orsay, France
¹² CNRS, 91405 Orsay, France
¹³ Institut d’Astrophysique de Paris, UMR 7095, CNRS, 98bis boulevard Arago, 75005 Paris, France
¹⁴ Sorbonne Universités, UPMC Univ. Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75005 Paris, France
¹⁵ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA

Received: 5 September 2014
Accepted: 3 March 2015

Abstract

Aims. We propose a new method of pushing Herschel to its faintest detection limits using universal trends in the redshift evolution of the far infrared over 24 μm colours in the well-sampled GOODS-North field. An extension to other fields with less multi-wavelength information is presented. This method is applied here to raise the contribution of individually detected Herschel sources to the cosmic infrared background (CIRB) by a factor 5 close to its peak at 250 μm and more than 3 in the 350 and 500 μm bands.

Methods. We produce realistic mock Herschel images of the deep PACS and SPIRE images of the GOODS–North field from the GOODS-Herschel key program and use them to quantify the confusion noise at the position of individual sources, i.e., estimate a “local confusion noise”. Two methods are used to identify sources with reliable photometric accuracy extracted using 24 μm prior positions. The clean index (CI), previously defined but validated here with simulations, which measures the presence of bright 24 μm neighbours and the photometric accuracy index (PAI) directly extracted from the mock Herschel images.

Results. Both methods converge to comparable depths and fractions of the CIRB resolved into sources individually detected with Herschel. After correction for completeness, thanks to our mock Herschel images, individually detected sources make up as much as 54% and 60% of the CIRB in the PACS bands down to 1.1 mJy at 100 μm and 2.2 mJy at 160 μm and 55, 33, and 13% of the CIRB in the SPIRE bands down to 2.5, 5, and 9 mJy at 250 μm, 350 μm, and 500 μm, respectively. The latter depths improve the detection limits of Herschel by factors of 5 at 250 μm, and 3 at 350 μm and 500 μm as compared to the standard confusion limit. Interestingly, the dominant contributors to the CIRB in all Herschel bands appear to be distant siblings of the Milky Way (z ~ 0.96 for λ< 300 μm) with a stellar mass of M_⋆ ~ 9 × 10¹⁰M_⊙.