# UV regulated star formation in high-redshift galaxies

## TL;DR

This study uses advanced cosmological simulations to investigate how UV radiation suppresses star formation in early galaxies by destroying molecular hydrogen, revealing delays in star formation onset depending on UV flux levels.

## Contribution

It introduces detailed simulations including H- photo-detachment and H2 self-shielding, providing new insights into UV regulation of primordial star formation.

## Key findings

- H2 formation is suppressed by UV flux, delaying star formation.
- Delay in star formation ranges from 100 to 230 million years.
- H2 self-shielding is essential for accurate cold gas estimates.

## Abstract

The first galaxies forming a few hundred million years after the Big Bang are the key drivers of cosmic evolution and ideal laboratories to study theories of galaxy formation. We here study the role of UV radiation in suppressing star formation in primordial galaxies by destroying molecular hydrogen, the main coolant in primordial gas and provide estimates of cold dense gas at the onset of star formation. To accomplish this goal, we perform three dimensional cosmological simulations of minihalos in different environments forming at $ z\sim 25$ by varying strength of background UV flux below the Lyman limit between 0.01-1000 in units of $\rm J_{21}=10^{-21}~erg/cm^2/s/Hz/sr$. Particularly, we include photo-detachment of $\rm H^-$, the self-shielding of $\rm H_2$ which both were neglected in previous studies and use updated reaction rates. Our results show that depending on the background level $\rm H_2$ formation is suppressed, delaying gravitational collapse until halos reach the atomic cooling limit. We find that the formation of cold dense molecular gas and subsequently star formation gets delayed by 100 to 230 Myr depending on the level of the background radiation and the growth history of the dark matter halos. The fraction of dense self-shielded gas is a strong function of the background flux and exponentially declines with the strength of incident UV flux above $\rm J_{21} \geq 1$. We find that taking into account $\rm H_2$ self-shielding is crucial for accurately estimating the amount of cold dense gas available for star formation.