A unified empirical model for infrared galaxy counts based on observed physical evolution of distant galaxies

TL;DR

This paper presents an empirical model that successfully reproduces infrared galaxy counts across multiple wavelengths by incorporating the physical evolution of main-sequence and starburst galaxies, validated against Herschel observations.

Contribution

It introduces a unified empirical model based on observed galaxy evolution and SEDs, accurately matching galaxy count measurements and revealing the roles of different galaxy types.

Findings

Model reproduces Herschel galaxy counts across wavelengths.

Main-sequence galaxies cause a radio count bump at 50 μJy.

The 2SFM decomposition effectively describes galaxy evolution.

Abstract

We reproduce the mid-infrared to radio galaxy counts with a new empirical model based on our current understanding of the evolution of main-sequence (MS) and starburst (SB) galaxies. We rely on a simple Spectral Energy Distribution (SED) library based on Herschel observations: a single SED for the MS and another one for SB, getting warmer with redshift. Our model is able to reproduce recent measurements of galaxy counts performed with Herschel, including counts per redshift slice. This agreement demonstrates the power of our 2 Star-Formation Modes (2SFM) decomposition for describing the statistical properties of infrared sources and their evolution with cosmic time. We discuss the relative contribution of MS and SB galaxies to the number counts at various wavelengths and flux densities. We also show that MS galaxies are responsible for a bump in the 1.4 GHz radio counts around 50 {\mu}Jy. Material of the model (predictions, SED library, mock catalogs...) is available online at http://irfu.cea.fr/Sap/Phocea/Page/index.php?id=537.