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Astron. Astrophys. 345, 29-35 (1999)

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I. A deep survey at 175 µm with ISO, preliminary results

J.L. Puget 1, G. Lagache 1, D.L. Clements 1, W.T. Reach 2, H. Aussel 3, F.R. Bouchet 4, C. Cesarsky 3, F.X. Désert 5, H. Dole 1, D. Elbaz 3, A. Franceschini 6, B. Guiderdoni 4 and A.F.M. Moorwood 7

1 Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, F-91405 Orsay Cedex, France
2 IPAC, California Institute of Technology, Pasadena, CA 91125, USA
3 Service d'Astrophysique/DAPNIA/DSM, CEA Saclay, F-91191 Gif sur Yvette, France
4 Institut d'Astrophysique de Paris, 98 bis Boulevard Arago F-75014 Paris, France
5 Observatoire de Grenoble, B.P. 53, 414 rue de la piscine, F-38041 Grenoble Cedex 9, France
6 Osservatorio Astronomico di Padova, I-35122 Padova, Italy
7 ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany

Received 15 July 1998 / Accepted 29 October 1998


FIRBACK is a deep survey conducted with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) at an effective wavelength of 175 µm. We present here results we have obtained on the first field, the so-called Marano1 which covers around 0.25 square degree. We find that the source density for objects with a flux above 200 mJy exceeds the counts expected for sources found in the IRAS deep surveys with a similar flux by about an order of magnitude. Such an excess was expected on the basis of the high far infrared background detected with the FIRAS and DIRBE instruments aboard the Cosmic Background Explorer (COBE). These sources are likely to be redshifted infrared galaxies. The steep number counts indicate strong cosmological evolution in this population. The detected sources account for only 10 [FORMULA] of the cosmic IR background. An extrapolation of the counts down to about 10 mJy would be needeed to account for the whole background at this wavelength.

Key words: cosmology: observations – infrared: galaxies – surveys – galaxies: evolution – galaxies: ISM

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999