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Astron. Astrophys. 323, 685-696 (1997)

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Galaxy evolution at low redshift?

II. Number counts and optical identifications of faint IRAS sources

E. Bertin 1, 2, M. Dennefeld 1, 3 and M. Moshir 4

1 Institut d'Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris, France
2 Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
3 Université Pierre & Marie Curie, 4, place Jussieu, F-75005 Paris, France
4 Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA

Received 10 July 1996 / Accepted 20 November 1996


We analyse a Far InfraRed (FIR) catalogue of galaxies at 60 µm with a flux limit of [FORMULA]  mJy, extracted from a deep subsample of the IRAS Faint Source Survey. Monte-Carlo simulations and optical identification statistics are used to put constraints on the evolution of galaxies in the FIR. We find evidence for strong evolution of IRAS galaxies, in luminosity [FORMULA] or density [FORMULA] for [FORMULA]  mJy, in agreement with previous claims. An excess of rather red faint optical counterparts with [FORMULA], consistent with the above evolution, is detected. We interpret these results as strong evolution at recent times among the starburst (or dusty AGN) population of merging/interacting galaxies. Most of these objects at moderate redshifts may pass unnoticed among the population of massive spirals in broad-band optical surveys, because of large amounts of dust extinction in their central regions. A possible link with the strong evolution observed in the optical for blue sub- [FORMULA] galaxies is discussed.

Key words: infrared: galaxies – galaxies: evolution – galaxies: starburst – galaxies: interactions – galaxies: fundamental parameters

Send offprint requests to: E. Bertin (bertin@iap.fr)

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998