The Dust-unbiased Cosmic Star-formation History from the 20 Cm Vla-cosmos Survey∗

We derive the cosmic star-formation history out to z = 1.3 using a sample of ∼350 radio-selected star-forming (SF) galaxies, a far larger sample than those in previous, similar studies. We attempt to differentiate between radio emission from active galactic nuclei and SF galaxies, and determine an evolving 1.4 GHz luminosity function (LF) based on these VLA-COSMOS SF galaxies. We precisely measure the high-luminosity end of the SF galaxy LF (star-formation rate 100M yr−1; equivalent to ultra-luminous IR galaxies) out to z = 1.3, finding a somewhat slower evolution than that previously derived from mid-infrared data. We find that more stars are forming in luminous starbursts at high redshift. We use extrapolations based on the local radio galaxy LF; assuming pure luminosity evolution, we derive L∗ ∝ (1 + z)2.1±0.2 or L∗ ∝ (1 + z)2.5±0.1, depending on the choice of the local radio galaxy LF. Thus, our radio-derived results independently confirm the ∼1 order of magnitude decline in the CSFH since z ∼ 1.