ISOPHOT 95 µm 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 μm imaging survey with ISOPHOT on board the Infrared Space Observatory, over a ∼1 deg² area within the Lockman Hole, which extends the statistics of our previous study (Rodighiero et al. \cite{Rodighiero03}). 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 S_{95 μm} ≥ 100 mJy, while the incompleteness can be quantified down to ∼30 mJy. The 95 μm galaxy counts reveal a steep slope at S_{95 μm} ≤100 mJy (α≃ 1.6), in excess of that expected for a non-evolving source population. In agreement with counts data from ISO at 15 and 175 μm, 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.

Based on observations obtained with the Infrared Space Observatory, an ESA science missions with instruments and contributions funded by ESA Member States and the USA (NASA).