The Cosmic Microwave Background and the Stellar Initial Mass Function

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.

arXiv comment9 pages, 5 figures. Published in MNRAS. Added further references

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• Thermal Regulation and the Star-Forming Main Sequence
• The Earliest Stage of Galactic Star Formation
• Stellar Initial Mass Function (IMF) Probed with Supernova Rates and Neutrino Background: Cosmic Average IMF Slope is $\simeq 2-3$ Similar to the Salpeter IMF
• Performance of Photometric Template Fitting for Ultra-High Redshift Galaxies
• Do Red Galaxies Form More Stars Than Blue Galaxies?
• Finding High-Redshift Galaxies with JWST