15 MicronInfrared Space ObservatoryObservations of the 1415+52 Canada‐France Redshift Survey Field: The Cosmic Star Formation Rate as Derived from Deep Ultraviolet, Optical, Mid‐Infrared, and Radio Photometry

Abstract

The Canada-France Redshift Survey 1452+52 field has been deeply imaged with the Infrared Space Observatory using ISOCAM through the LW3 filter (12-18 μm). Careful data analysis and comparison with deep optical and radio data have allowed us to generate a catalog of 78 15 μm sources with both radio and optical identifications. They are redder and lie at higher redshift than I-band-selected galaxies, with most of them being star-forming galaxies. We have considered the galaxies detected at radio and 15 μm wavelengths, which potentially include all strong and heavily extincted starbursts, up to z=1. Spectral energy distributions (SEDs) for each of the sources have been derived using deep radio, mid-IR, near-IR, optical, and UV photometry. The sources were then spectrally classified by comparing with SEDs of well-known nearby galaxies. By deriving their far-IR luminosities by interpolation, we can estimate their star formation rate (SFR) in a way that does not depend sensitively on the extinction. Between 35% and 85% of the star formation at z≤1 is related to IR emission, and the global extinction is in the range AV=0.5-0.85. While heavily extincted starbursts with SFRs in excess of 100 M☉ yr-1 constitute less than 1% of all galaxies, they contribute about 18% of the SFR density out to z=1. Their morphologies range from S0 to Sab, and more than a third are interacting systems. The SFR derived by far-IR fluxes is likely to be ~2.9 times higher than those previously estimated from UV fluxes. The derived stellar mass formed since the redshift of 1 could be too high when compared with the present-day stellar mass density. This might be due to an initial mass function in distant star-forming galaxies different from the solar neighborhood one or an underestimate of the local stellar mass density.