EDP Sciences
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Volume 427, Number 3, December I 2004
Page(s) 773 - 783
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20041252

A&A 427, 773-783 (2004)
DOI: 10.1051/0004-6361:20041252

ISOCAM observations in the Lockman Hole

II. The 14.3 $\mu$m deep survey: Data reduction, catalogue and source counts
G. Rodighiero1, C. Lari2, D. Fadda3, A. Franceschini1, D. Elbaz4 and C. Cesarsky5

1  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
    e-mail: rodighiero@pd.astro.it
2  Istituto di Radioastronomia del CNR (IRA), via Gobetti 101, 40129 Bologna, Italy
3  Spitzer Science Center, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91126, USA
4  CEA, DSM, DAPNIA, Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France
5  European Southern Observatory (ESO), Karl-Schwarzschild-Strasse, 2, 85748 Garching bei München, Germany

(Received 6 May 2004 / Accepted 5 July 2004)

We present a new analysis of the ISOCAM 14.3  $\mu$m deep survey in a 20  $\times$ 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. (2001). We have produced a catalogue of 283 sources detected above the 5- $\sigma$ 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 (5 $\sigma$ 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  $\mu$m sources do not have an optical counterpart down to r'=25 mag. We use the 6.7/14.3  $\mu$m 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  $\mu$m 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.

Key words: infrared: galaxies -- galaxies: photometry -- galaxies: statistics -- galaxies: evolution -- cosmology: observations -- methods: data analysis

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