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Astron. Astrophys. 351, L37-L40 (1999)

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Letter to the Editor

Source counts from the 15 µm ISOCAM Deep Surveys *

D. Elbaz 1, C.J. Cesarsky 1,2, D. Fadda 1, H. Aussel 1,3, F.X. Désert 4, A. Franceschini 5, H. Flores 1, M. Harwit 6, J.L. Puget 7, J.L. Starck 1, D.L. Clements 7, L. Danese 8, D.C. Koo 9 and R. Mandolesi 10

1 CEA Saclay - Service d'Astrophysique, Orme des Merisiers, 91191 Gif-sur-Yvette Cédex, France
2 European Southern Observatory, Karl-Schwarzchild-Strasse 2, 85748 Garching bei München, Germany
3 Osservatorio di Padova, Vicolo Osservatorio, 5, 35122 Padova, Italy
4 Observatoire de Grenoble, B.P. 53, 414 rue de la piscine, 38041 Grenoble Cedex 9, France
5 Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio, 5, 35122 Padova, Italy
6 511 H Street S.W., Washington, DC 20024-2725; also Cornell University, USA
7 Université Paris XI, Institut d'Astrophysique Spatiale, Bât 121, 91405 Orsay Cédex, France
8 SISSA, via Beirut 2-4, 34013 Trieste, Italy
9 University of California, UCO/Lick Obs., Santa Cruz, CA 95064, USA
10 Bologna Radio Astronomy Institute, via Gobetti 101, 40129 Bologna, Italy

Received 2 September 1999 / Accepted 19 October 1999

Abstract

We present the results of the five mid-IR 15 µm (12-18 µm LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field. The roughly 1000 sources detected, 600 of which have a flux above the 80% completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to [FORMULA]5 mJy. By adding the ISOCAM surveys of the HDF-North and South (plus flanking fields) and the lensing cluster A2390 at low fluxes and IRAS at high fluxes, we cover four decades in flux from 50 µJy to [FORMULA]0.3 Jy. The slope of the differential counts is very steep ([FORMULA]) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of [FORMULA]. When compared with no-evolution models based on IRAS, our counts show a factor [FORMULA] 10 excess at 400 µJy, and a fast convergence, with [FORMULA] at lower fluxes.

Key words: galaxies: evolution – infrared: galaxies

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA

Send offprint requests to: delbaz@cea.fr

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© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999
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