# The Comoving Infrared Luminosity Density: Domination of Cold Galaxies across 0<z<1

## TL;DR

This study shows that cold galaxies significantly contribute to the infrared luminosity density and star formation rate from the local universe up to redshift 1, challenging previous assumptions about galaxy populations at different epochs.

## Contribution

It provides a detailed analysis of the IR spectral energy distributions of galaxies across 0<z<1, highlighting the dominance of cold galaxies in the IR luminosity density over this range.

## Key findings

- Cold galaxies dominate IR luminosity density at 0<z<1.
- Luminous IR galaxies are mostly cold at higher redshifts.
- Local luminous galaxies are not representative of high-redshift populations.

## Abstract

In this paper we examine the contribution of galaxies with different infrared (IR) spectral energy distributions (SEDs) to the comoving infrared luminosity density, a proxy for the comoving star formation rate (SFR) density. We characterise galaxies as having either a cold or hot IR SED depending upon whether the rest-frame wavelength of their peak IR energy output is above or below 90um. Our work is based on a far-IR selected sample both in the local Universe and at high redshift, the former consisting of IRAS 60um-selected galaxies at z<0.07 and the latter of Spitzer 70um selected galaxies across 0.1<z<1. We find that the total IR luminosity densities for each redshift/luminosity bin agree well with results derived from other deep mid/far-IR surveys. At z<0.07 we observe the previously known results: that moderate luminosity galaxies (L_IR<10^11 Lsun) dominate the total luminosity density and that the fraction of cold galaxies decreases with increasing luminosity, becoming negligible at the highest luminosities. Conversely, above z=0.1 we find that luminous IR galaxies (L_IR>10^11 Lsun), the majority of which are cold, dominate the IR luminosity density. We therefore infer that cold galaxies dominate the IR luminosity density across the whole 0<z<1 range, hence appear to be the main driver behind the increase in SFR density up to z~1 whereas local luminous galaxies are not, on the whole, representative of the high redshift population.