Radiative cooling functions for primordial molecules

TL;DR

This paper calculates radiative cooling functions for primordial molecules like HD, HeH+, and LiH, providing analytic fits to understand their role in early universe structure formation.

Contribution

It presents new radiative cooling functions for several primordial molecules and ions, with analytic temperature-dependent fits, enhancing models of early universe cooling processes.

Findings

Cooling functions for HD, HD+, HeH+, LiH, LiH+ derived.

Cooling functions for H3+ and H2D+ also evaluated.

Analytic fits provided for use in cosmological models.

Abstract

Cooling of primordial gas plays a crucial role in the birth of the first structures in our Universe. Due to the low fractional abundance of molecular species at high redshifts, spontaneous emission rather than collisions represents the most efficient way to cool the pristine plasma. In the present work, radiative cooling functions are evaluated for the diatomic species HD, HD$^+$, HeH$^+$, LiH and LiH$^+$. Cooling functions for the triatomic ions H$_3^+$ and H$_2$D$^+$ are also considered. Analytic fits as functions of temperature are provided.