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Astron. Astrophys. 343, 389-398 (1999)

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Deep Galaxy survey at 6.75µm with the ISO satellite *

H. Flores 1, F. Hammer 1, F.X. Désert 2, C. Césarsky 3, T. Thuan 4, D. Crampton 5, S. Eales 6, O. Le Fèvre 1, S.J. Lilly 7, A. Omont 8 and D. Elbaz 3

1 Observatoire de Meudon, DAEC and URA 173, associé au CNRS et à l'Université Paris 7, F-92195 Meudon Cedex, France
2 Institut d'Astrophysique Spatiale, Orsay, France
3 Service d'Astrophysique, CEA, France
4 University of Virginia, USA
5 Dominion Astrophysical Observatory, HIA, National Research Council of Canada, V8X 4M6, Canada
6 University of Cardiff, UK
7 Department of Astronomy, University of Toronto, Toronto, Canada
8 Institute d'Astrophysique de Paris, France

Received 5 January 1998 / Accepted 7 September 1998


Deep 6.75µm mid-IR ISOCAM observations were obtained from the Canada-France Redshift Survey (CFRS) 1415+52 field with the Infrared Space Observatory. The identification of the sources with optical counterparts is described in detail, and a classification scheme is devised which depends on the S/N of the detection and the inverse probability of chance coincidence. 83% of the 54 ISOCAM sources are identified with [FORMULA]23.5 counterparts. The [FORMULA] colors, radio properties, spectrophotometric properties and frequency of nuclear activity of these counterparts differ on average from those of typical CFRS galaxies. CFRS spectra are available for 21 of the sources which have [FORMULA] (including 7 stars). Most of the strongest sources are stars or AGN. Among the non-stellar counterparts with spectra, 40% are AGNs, and 53% are galaxies that display star formation activity and/or significant contributions of A stars. The ISOCAM sources also display an IR excess, even when compared with heavily-reddened local starburst galaxies. An upper limit of 30% of extragalactic ISO sources could be at [FORMULA] of the 44 [FORMULA] sources which are non-stellar (7 "spectroscopic" and 3 "photometric" stars excluded).

Key words: galaxies: active – galaxies: evolution – galaxies: statistics – infrared: galaxies

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

Send offprint requests to: H. Flores, Observatoire de Paris, F-92195 Meudon Cedex, France

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999