The contribution of starbursts and normal galaxies to infrared luminosity functions at z < 2

TL;DR

This paper introduces a parameter-less model to predict the infrared luminosity function at z<2, successfully matching observations and quantifying starburst contributions without tuning, based on galaxy evolution observables.

Contribution

It presents a novel, self-consistent framework that predicts IR luminosity functions using only three key galaxy evolution observables, without any parameter tuning.

Findings

IR luminosity functions are well matched at all z<2

Starburst contribution to star formation rate density is 8-14%

Luminosity threshold for starburst dominance increases from 10^11.4 to 10^12.8 Lsun over z<2

Abstract

We present a parameter-less approach to predict the shape of the infrared (IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and relies on only three observables: (1) the redshift evolution of the stellar mass function for star-forming galaxies, (2) the evolution of the specific star formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian decomposition of the sSFR-distribution at fixed stellar mass into a contribution (assumed redshift- and mass-invariant) from main-sequence and starburst activity. This self-consistent and simple framework provides a powerful tool for predicting cosmological observables: observed IR LFs are successfully matched at all z < 2, suggesting a constant or only weakly redshift-dependent contribution (8-14%) of starbursts to the star formation rate density. We separate the contributions of main-sequence and starburst activity to the global IR LF at all redshifts. The luminosity threshold above which the starburst component dominates the IR LF rises from log(LIR/Lsun) = 11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR in main-sequence galaxies.