# Ionization degree and magnetic diffusivity in the primordial star-forming clouds

## TL;DR

This study investigates the ionization degree and magnetic diffusivity in primordial star-forming clouds, revealing enhanced ionization due to lithium ionization and its implications for magnetic field dissipation and star formation processes.

## Contribution

It introduces a minimal chemical network accurately modeling ionization in primordial clouds, highlighting the role of lithium ionization and its impact on magnetic diffusivity.

## Key findings

- Ionization degree is 100-1000 times higher than previous estimates due to lithium ionization.
- Magnetic field dissipation is negligible for large-scale coherent fields during collapse.
- Strong magnetic fields can slow collapse and lower temperature through ambipolar diffusion heating.

## Abstract

Magnetic fields play such roles in star formation as the angular momentum transport in star-forming clouds, thereby controlling circumstellar disc formation and even binary star formation efficiency. The coupling between the magnetic field and gas is determined by the ionization degree in the gas. Here, we calculate the thermal and chemical evolution of the primordial gas by solving chemical reaction network where all the reactions are reversed. We find that at ~ 10^14-10^18 /cm^3, the ionization degree becomes 100-1000 times higher than the previous results due to the lithium ionization by thermal photons trapped in the cloud, which has been omitted so far. We construct the minimal chemical network which can reproduce correctly the ionization degree as well as the thermal evolution by extracting 36 reactions among 13 species. Using the obtained ionization degree, we evaluate the magnetic field diffusivity. We find that the field dissipation can be neglected for global fields coherent over > a tenth of the cloud size as long as the field is not so strong as to prohibit the collapse. With magnetic fields strong enough for ambipolar diffusion heating to be significant, the magnetic pressure effects to slow down the collapse and to reduce the compressional heating become more important, and the temperature actually becomes lower than in the no-field case.