Consequences of cosmic microwave background-regulated star formation

TL;DR

This paper explores how the cosmic microwave background (CMB) might regulate star formation at high redshifts, predicting observable signatures that could explain certain features of early stellar populations.

Contribution

It identifies five testable observational signatures of CMB-regulated star formation and assesses their potential impact on understanding early universe star formation.

Findings

CMB temperature floor influenced most stars at z=3-6

Predicted higher supernova rates at high redshift

Possible explanation for bimodal metallicity distribution in globular clusters

Abstract

It has been hypothesized that the cosmic microwave background (CMB) provides a temperature floor for collapsing protostars that can regulate the process of star formation and result in a top-heavy initial mass function at high metallicity and high redshift. We examine whether this hypothesis has any testable observational consequences. First we determine, using a set of hydrodynamic galaxy formation simulations, that the CMB temperature floor would have influenced the majority of stars formed at redshifts between z=3 and 6, and probably even to higher redshift. Five signatures of CMB-regulated star formation are: (1) a higher supernova rate than currently predicted at high redshift; (2) a systematic discrepancy between direct and indirect measurements of the high redshift star formation rate; (3) a lack of surviving globular clusters that formed at high metallicity and high redshift; (4) a more rapid rise in the metallicity of cosmic gas than is predicted by current simulations; and (5) an enhancement in the abundances of alpha elements such as O and Mg at metallicities -2 < [Fe/H] < -0.5. Observations are not presently able to either confirm or rule out the presence of these signatures. However, if correct, the top-heavy IMF of high-redshift high-metallicity globular clusters could provide an explanation for the observed bimodality of their metallicity distribution.