Carbon-Enhanced Metal-Poor Stars, the Cosmic Microwave Background, and the Stellar IMF in the Early Universe

TL;DR

This paper explores how the cosmic microwave background influenced the initial mass function of early stars, predicting increased carbon-enhanced metal-poor stars at lower metallicities and older populations, impacting our understanding of early star formation.

Contribution

It introduces the CMB-IMF hypothesis, linking the CMB to variations in the stellar initial mass function and CEMP star fractions, supported by observational evidence.

Findings

CEMP star fraction increases with decreasing metallicity.

Older stellar populations show higher CEMP fractions.

Spatial variations in CEMP stars may explain survey discrepancies.

Abstract

The characteristic mass of stars at early times may have been higher than today owing to the cosmic microwave background (CMB). This study proposes that (1) the testable predictions of this "CMB-IMF" hypothesis are an increase in the fraction of carbon-enhanced metal-poor (CEMP) stars with declining metallicity and an increase from younger to older populations at a single metallicity (e.g. disk to halo), and (2) these signatures are already seen in recent samples of CEMP stars and can be better tested with anticipated data. The expected spatial variation may explain discrepancies of CEMP frequency among published surveys. The ubiquity and time dependence of the CMB will substantially alter the reconstruction of star formation histories in the Local Group and early Universe.