THE CONTRIBUTION OF STARBURSTS AND NORMAL GALAXIES TO INFRARED LUMINOSITY FUNCTIONS AT <i>z</i> &lt; 2

Abstract

We present a parameter-less approach to predict the shape of the infrared\n(IR) luminosity function (LF) at redshifts z &lt; 2. It requires no tuning and\nrelies on only three observables: (1) the redshift evolution of the stellar\nmass function for star-forming galaxies, (2) the evolution of the specific star\nformation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian\ndecomposition of the sSFR-distribution at fixed stellar mass into a\ncontribution (assumed redshift- and mass-invariant) from main-sequence and\nstarburst activity. This self-consistent and simple framework provides a\npowerful tool for predicting cosmological observables: observed IR LFs are\nsuccessfully matched at all z &lt; 2, suggesting a constant or only weakly\nredshift-dependent contribution (8-14%) of starbursts to the star formation\nrate density. We separate the contributions of main-sequence and starburst\nactivity to the global IR LF at all redshifts. The luminosity threshold above\nwhich the starburst component dominates the IR LF rises from log(LIR/Lsun) =\n11.4 to 12.8 over 0 &lt; z &lt; 2, reflecting our assumed (1+z)^2.8-evolution of sSFR\nin main-sequence galaxies.\n