Faint Radio Sources and Star Formation History.pdf

a r X i v : a s t r o - p h / 9 9 0 4 0 3 6 v 2 1 J u l 1 9 9 9 FAINT RADIO SOURCES AND STAR FORMATION HISTORY Deborah B. Haarsma1, R. Bruce Partridge1, Ian Waddington2, and Rogier A. Windhorst2 For inclusion in the CD-ROM Proceedings of the 19th Texas Symposium on Relativistic Astrophysics, held December 1998 (1) Haverford College Haverford, Pennsylvania 19041 USA Email: dhaarsma@haverford.edu (2) Arizona State University Department of Physics and Astronomy Tempe, Arizona 85287-1504 USA Abstract. Faint extragalactic radio sources provide important information about the global history of star formation. Sensitive radio observations of the Hubble Deep Field and other fields have found that sub-mJy radio sources are predominantly associated with star formation activity rather than AGN. Radio observations of star forming galaxies have the advantage of being independent of extinction by dust. We use the FIR-radio correlation to compare the radio and FIR backgrounds, and make several conclusions about the star forming galaxies producing the FIR background. We then use the redshift distribution of faint radio sources to determine the evolution of the radio luminosity function, and thus estimate the star formation density as a function of redshift. 1. Introduction Faint radio sources provide important information about global star formation history. Sensitive radio observations of the Hubble Deep Field (HDF) (Richards et al 1998, [1]) and other fields well-studied at optical wavelengths (Windhorst et al 1995, [2], Fomalont et al 1991, [3]) have shown that sub-mJy radio sources are predominantly associated with star formation activity rather than active galactic nuclei (AGN). The radio luminosity of a galaxy is a reliable predictor of the star formation rate (SFR) for local galaxies (Condon 1992, [4] Cram et al 1998, [5]). Estimates of star formation based on radio observations also have the advantage of being independent of extinction by dust, which has caused much di