FIRBACK: III. Catalog, source counts, and cosmological implications of the 170 μm ISO deep survey^*,**

¹ Institut d'Astrophysique Spatiale, bâtiment 121, Université Paris Sud, 91405 Orsay Cedex, France
² Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721, USA
³ Institut d'Astrophysique de Paris, 98bis Bd. Arago, 75014 Paris, France
⁴ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁵ Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
⁶ Department of Physics & Astronomy, Cardiff University, PO Box 813, Cardiff CF22 3YB, UK
⁷ Laboratoire d'Astrophysique, Obs. de Grenoble, BP 53, 414 Av. de la piscine, 38031 Grenoble Cedex 9, France
⁸ Service d'Astrophysique, DAPNIA, DSM, CEA Saclay, 91191, Gif-sur-Yvette, France
⁹ Physics and Astronomy Departments, University of California, Santa Cruz, CA 95064, USA
¹⁰ Astronomy Departement, Padova University, Vicolo Osservatorio, 5, 35122 Padova, Italy
¹¹ 511 H. Street S. W., Washington DC 20024-2725, USA; also Cornell University
¹² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹³ Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BZ, UK
¹⁴ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QJ, UK
¹⁵ IPAC, California Institute of Technology, Pasadena, CA 91125, USA

Corresponding author: H. Dole, hdole@as.arizona.edu

Received: 23 January 2001
Accepted: 5 March 2001

Abstract

The FIRBACK (Far Infrared BACKground) survey is one of the deepest imaging surveys carried out at 170 μm with ISOPHOT onboard ISO, and is aimed at the study of the structure of the Cosmic Far Infrared Background. This paper provides the analysis of resolved sources. After a validated process of data reduction and calibration, we perform intensive simulations to optimize the source extraction, measure the confusion noise ( mJy), and give the photometric and astrometric accuracies. 196 galaxies with flux are detected in the area of 3.89 square degrees. Counts of sources with flux present a steep slope of on a differential "log N-log S"plot between 180 and 500 mJy. As a consequence, the confusion level is high and will impact dramatically on future IR deep surveys. This strong evolution, compared with a slope of 2.5 from Euclidian geometry, is in line with models implying a strongly evolving Luminous Infrared Galaxy population. The resolved sources account for less than 10% of the Cosmic Infrared Background at 170 μm, which is expected to be resolved into sources in the 1 to 10 mJy range.