The VLA-COSMOS 3 GHz Large Project: Cosmic star formation history sincez~ 5

Abstract

We make use of the deep Karl G. Jansky Very Large Array (VLA) COSMOS radio observations at 3 GHz to infer radio luminosity functions of star-forming galaxies up to redshifts of z ∼ 5 based on approximately 6 000 detections with reliable optical counterparts. This is currently the largest radio-selected sample available out to z ∼ 5 across an area of 2 square degrees with a sensitivity of rms ≈ 2.3 µJy beam −1 . By fixing the faint and bright end shape of the radio luminosity function to the local values, we find a strong redshift trend that can be fitted with a pure luminosity evolution L 1.4 GHz ∝ (1 + z) (3.16±0.2)−(0.32±0.07)z . We estimate star formation rates (SFRs) from our radio luminosities using an infrared (IR)-radio correlation that is redshift dependent. By integrating the parametric fits of the evolved luminosity function we calculate the cosmic SFR density (SFRD) history since z ∼ 5. Our data suggest that the SFRD history peaks between 2 < z < 3 and that the ultraluminous infrared galaxies (ULIRGs; 100 M ⊙ yr −1 < SFR < 1000 M ⊙ yr −1 ) contribute up to ∼25% to the total SFRD in the same redshift range. Hyperluminous infrared galaxies (HyLIRGs; SFR > 1000 M ⊙ yr −1 ) contribute an additional 2% in the entire observed redshift range. We find evidence of a potential underestimation of SFRD based on ultraviolet (UV) rest-frame observations of Lyman break galaxies (LBGs) at high redshifts (z 4) on the order of 15-20%, owing to appreciable star formation in highly dust-obscured galaxies, which might remain undetected in such UV observations.

Stellar Mass Function of Active and Quiescent Galaxies via the Continuity Equation

“…The UV data considerably underestimate the SFR function for SFRsṀ ⋆ 30 M ⊙ yr −1 , because of strong dust extinction. Interestingly, the shape of the SFR function foṙ M ⋆ 10 2 M ⊙ yr −1 , which so far has been probed only indirectly at z 4 due to sensitivity limits in current wide-areas far-IR surveys, is found to agree out to z 6 with the constraints from the recent VLA-COSMOS radio survey (Novak et al 2017) and from the few individual galaxies detected at z 5 with ALMA and SMA (e.g., Riechers et al 2017;Zavala et al 2017). We shall demonstrate via the continuity equation that a robust probe on the bright end of the SFR function at highredshift z 4 is provided by the galaxy stellar mass function.…”

“…Solid lines refer to the rendition from UV plus far-IR/sub-mm/radio data; dotted lines (only plotted at z ≈ 0 and 1) refer to the rendition from UV data (dust corrected according to standard prescriptions based on the UV slope). UV data (open symbols) are from van der Burg et al (2010;diamonds), Bouwens et al (2016Bouwens et al ( , 2017pentagons), inverse triangles), Cucciati et al (2012;triangles), Wyder et al (2005;spirals), Oesch et al (2010;crosses), Alavi et al (2016;asterisks); far-IR/sub-mm data from Gruppioni et al (2015;hexagons), Magnelli et al (2013;circles), Gruppioni et al (2013;squares), Lapi et al (2011;stars), and Cooray et al (2014;pacmans); radio data from Novak et al (2017;clovers). extinction law, but note that switching to a Small Magellanic Cloud (SMC) extinction law affects mildly the SFR function at the faint end (see also Sect.…”

“…The first concerns the discovery of an abundant population of dusty star-forming galaxies at redshifts z 1, that has been shown to be responsible for the bulk of the cosmic star formation history, in particular around the crucial redshifts z ≈ 2 − 3 where it peaks (e.g., Gruppioni et al 2013;Rowan-Robinson et al 2016;Bourne et al 2017;Dunlop et al 2017;Novak et al 2017), and to be present even out to z 6 (e.g., Cooray et al 2014;Riechers et al 2017;Zavala et al 2017). Such achievement has become feasible only recently thanks to wide-area far-IR/sub-mm surveys conducted by Herschel, ASTE/AzTEC, APEX/LABOCA, JCMT/SCUBA2, and ALMA-SPT (e.g., Gruppioni et al 2013Gruppioni et al , 2015Lapi et al 2011;Weiss et al 2013;Strandet et al 2016;Koprowski et al 2014Koprowski et al , 2016, in many instances eased by gravitational lensing from foreground objects (e.g., Negrello et al 2014Negrello et al , 2017Nayyeri et al 2016).…”

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

“…The usually observed spread in spectral indices is σ ≈ 0.35 (e.g., Smolčić et al 2017a) and the uncertainty of the spectral index can induce significant errors in the derived radio luminosity for a single object. However, on a statistical basis the symmetry of the spread is expected to cancel out the variations yielding a valid average luminosity for the given population (see also Novak et al 2017;Delhaize et al 2017;Smolčić et al 2017b, for more specific discussions on this).…”

The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release

“…Source counts at 1.4 GHz depend on the steepness of the counts at 3 GHz and the spread of the spectral indices. We leave the analysis of the potential bias in source counts due to this effect to an upcoming paper (Novak et al 2017).…”