The evolution of the UV-to-mm extragalactic background light: evidence for a top-heavy initial mass function?

TL;DR

This paper uses a galaxy formation model with a top-heavy initial mass function to accurately predict the UV-to-mm extragalactic background light, matching observations and providing insights into galaxy evolution.

Contribution

It demonstrates that a top-heavy IMF in starbursts is essential for reproducing the observed EBL and galaxy counts across the UV-to-mm spectrum.

Findings

Predicted EBL matches recent observations across the spectrum.

Approximately 90% of EBL is produced at redshifts less than 2.

Universal IMF models perform poorly compared to top-heavy IMF models.

Abstract

We present predictions for the UV-to-mm extragalactic background light (EBL) from a recent version of the GALFORM semi-analytical model of galaxy formation which invokes a top-heavy stellar initial mass function (IMF) for galaxies undergoing dynamically-triggered bursts of star formation. We combine GALFORM with the GRASIL radiative transfer code for computing fully self-consistent UV-to-mm spectral energy distributions for each simulated galaxy, accounting for the absorption and re-emission of stellar radiation by interstellar dust. The predicted EBL is in near-perfect agreement with recent observations over the whole UV-to-mm spectrum, as is the evolution of the cosmic spectral energy distribution over the redshift range for which observations are available ($z\lesssim1$). We show that approximately 90~per~cent of the EBL is produced at $z<2$ although this shifts to higher redshifts for sub-mm wavelengths. We assess whether the top-heavy IMF in starbursts is necessary in order to reproduce the EBL at the same time as other key observables, and find that variant models with a universal solar-neighborhood IMF display poorer agreement with EBL observations over the whole UV-to-mm spectrum and fail to match the counts of galaxies in the sub-mm.