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Session 63 - Surveys of Galaxies.
Oral session, Thursday, January 08

[63.05] Deep 175 Micron Counts with ISO: A New Population?

D. L. Clements, J. Puget, G. Lagache, W. Reach, R. Gispert, H. Dole (Inst. d'Astrophysique Spatial, France), C. Cesarsky, D. Elbaz, H. Aussel (Service d'Astrophysique, France), F. Bouchet, B. Guiderdoni, A. Omont (IAP, France), F. Desert (Grenoble Obs., France), A. Franceschini (U. Padova, Italy)

The IRAS satellite demonstrated the existence of a population of galaxies with strong far-infrared (FIR) emission. IRAS observations have also shown that this population evolves rapidly locally, and may be a cosmologically important population. The recent tentative detection of a Cosmic Infrared Background (Puget et al. 1996, Aamp;A 308, L5) raises the possibility that there is a large population of distant FIR luminous galaxies. We have thus conducted a deep survey at 175\mum using the ISO satellite in the Marano Field. This field was selected for its low HI and IRAS cirrus emission. The area covered by our survey is \sim0.25 deg^2, and we reach a 1\sigma sensitivity limit of \sim10 mJy. This survey thus represents one of the deepest fields ever observed at these long wavelengths. We find a surprisingly large number of point sources in this field, more than would be predicted by an extrapolation of the IRAS counts, but the integrated flux is consistent with the putative FIR background. We will extend this survey to a larger area before the end of the ISO mission, and ground-based followup observations are already underway. We should thus soon know the nature and significance of what may be a new population.

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