ISOCAM observations in the Lockman Hole . II. The 14.3 µm deep survey: Data reduction, catalogue and source counts

Abstract

We present a new analysis of the ISOCAM 14.3 μm deep survey in a 20 × 20 square arcmins area in the Lockman Hole. This survey is intermediate between the ultra-deep surveys and the shallow surveys in the ELAIS fields. The data have been analyzed with the method presented by Lari et al. (\cite{Lar01}). We have produced a catalogue of 283 sources detected above the 5-σ threshold, with fluxes in the interval 0.1-8 mJy. The catalogue is 90% complete at 1 mJy. The positional accuracy, estimated from the cross-correlation of infrared and optical sources, is around 1.5 arcsec. The search for the optical counterparts of the sources in the survey is performed on a medium-deep r' band optical image (5σ depth of r'=25), making use of the radio detections when available. The photometry has been checked through simulations and by comparing the data with those presented in a shallower and more extended ISOCAM survey in the Lockman Hole, that we have presented in a companion paper. Only 15% of the 14.3 μm sources do not have an optical counterpart down to r'=25 mag. We use the 6.7/14.3 μm colour as a star/galaxy separator, together with a visual inspection of the optical image and an analysis of the observed Spectral Energy Distribution of the ISOCAM sources. The stars in the sample turn out to be only 6% of the sample. We discuss the 14.3 μm counts of extragalactic sources, combining our catalogue with that obtained from the shallower ISOCAM survey. The data in the two surveys are consistent, and our results fully support the claims in previous works for the existence of an evolving population of infrared galaxies, confirming the evident departure from non-evolutionary model predictions.

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

Tables 2 and 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/773

Table \ref{tab:obsparam} and Figs. \ref{fig:sky_map}, \ref{fig:LH_map} and \ref{fig:opt_1}-\ref{fig:opt_3} are only available in electronic form at http://www.edpsciences.org