Chemistry and cooling in metal-free and metal-poor gas

TL;DR

This paper reviews key uncertainties in the chemistry and cooling processes of primordial and low-metallicity gas, focusing on HD cooling, metal-line and dust cooling, reaction rate uncertainties, and grain surface chemistry at high redshifts.

Contribution

It identifies and summarizes four critical areas of uncertainty affecting the understanding of gas cooling and chemistry in early universe conditions.

Findings

HD cooling may significantly influence primordial gas evolution

Metal-line and dust cooling are crucial at low metallicities

Uncertainties in reaction rates impact chemical modeling accuracy

Abstract

I summarize four of the most important areas of uncertainty in the study of the chemistry and cooling of gas with zero or very low metallicity. These are: i) the importance and effects of HD cooling in primordial gas; ii) the importance of metal-line and dust cooling in low metallicity gas; iii) the impact of the large uncertainties that exist in the rate coefficients of several key reactions involved in the formation of H2; and iv) the effectiveness of grain surface chemistry at high redshifts.