ISOPHOT 95 micron observations in the Lockman Hole - The catalogue and an assessment of the source counts

Abstract

We report results from a new analysis of a deep 95 micron imaging survey with ISOPHOT on board the Infrared Space Observatory, over a ~1 square degree area within the Lockman Hole, which extends the statistics of our previous study (Rodighiero et al. 2003). Within the survey area we detect sixty-four sources with S/N>3 (roughly corresponding to a flux limit of 16 mJy). Extensive simulations indicate that the sample is almost complete at fluxes > 100 mJy, while the incompleteness can be quantified down to ~30 mJy. The 95 micron galaxy counts reveal a steep slope below 100 mJy (alpha~1.6), in excess of that expected for a non-evolving source population. In agreement with counts data from ISO at 15 and 175 micron, this favours a model where the IR populations evolve both in number and luminosity densities. We finally comment on some differences found with other ISO results in this area.

4 pages, accepted by Astronomy and Astrophysics Letter