The Cosmic Microwave Background and the Stellar Initial Mass Function

TL;DR

This paper explores how increased cosmic microwave background temperature at high redshifts influences the stellar initial mass function, affecting galaxy evolution models and measurements of stellar properties.

Contribution

It introduces the impact of CMB-induced heating on the initial mass function, highlighting its significance for high-redshift galaxy observations and stellar mass estimations.

Findings

CMB heating makes the IMF more bottom-light at high redshifts.

Photometric estimates may overstate stellar masses and SFRs in early galaxies.

This effect could resolve issues in galactic halo chemical evolution.

Abstract

We argue that an increased temperature in star-forming clouds alters the stellar initial mass function to be more bottom-light than in the Milky Way. At redshifts $z \gtrsim 6$, heating from the cosmic microwave background radiation produces this effect in all galaxies, and it is also present at lower redshifts in galaxies with very high star formation rates (SFRs). A failure to account for it means that at present, photometric template fitting likely overestimates stellar masses and star formation rates for the highest-redshift and highest-SFR galaxies. In addition this may resolve several outstanding problems in the chemical evolution of galactic halos.