The statistical properties of stars at redshift, z=5, compared with the present epoch

TL;DR

This study compares the statistical properties of stars and brown dwarfs formed at redshift z=5 with different metallicities to present-day star formation, revealing how cosmic microwave background radiation influences stellar mass distribution and multiplicity.

Contribution

It provides the first detailed comparison of star formation properties at z=5 across varying metallicities, highlighting the impact of the cosmic microwave background on stellar mass and multiplicity.

Findings

Stellar mass distribution at z=5 varies with metallicity, unlike at z=0.

Higher metallicity at z=5 leads to fewer brown dwarfs and low-mass stars.

Metal-rich gas at z=5 cannot cool as efficiently, affecting fragmentation.

Abstract

We report the statistical properties of stars and brown dwarfs obtained from three radiation hydrodynamical simulations of star cluster formation with metallicities of 1, 1/10 and 1/100 of the solar value. The star-forming clouds are subjected to cosmic microwave background radiation that is appropriate for star formation at a redshift z=5. The results from the three calculations are compared to each other, and to similar previously published calculations that had levels of background radiation appropriate for present-day (z=0) star formation. Each of the calculations treat dust and gas temperatures separately and include a thermochemical model of the diffuse interstellar medium. We find that whereas the stellar mass distribution is insensitive to the metallicity for present-day star formation, at z=5 the characteristic stellar mass increases with increasing metallicity and the mass distribution has a deficit of brown dwarfs and low-mass stars at solar metallicity compared to the Galactic initial mass function. We also find that the multiplicity of M-dwarfs decreases with increasing metallicity at z=5. These effects are a result of metal-rich gas being unable to cool to as low temperatures at z=5 compared to at z=0 due to the hotter cosmic microwave background radiation, which inhibits fragmentation at high densities.