# Dark-ages reionization and galaxy formation simulation - IX. Economics of reionizing galaxies

## TL;DR

This study uses high-resolution hydrodynamical simulations to analyze the gas consumption and star formation processes in high-redshift galaxies, revealing that molecular gas is rapidly consumed and that traditional self-regulation models do not apply to early dwarf galaxies.

## Contribution

It provides new insights into the gas dynamics and star formation limitations in early galaxies, challenging the assumption of self-regulation in dwarf galaxy growth during reionization.

## Key findings

- Molecular gas reserves are consumed within 300 Myr during rapid galaxy growth.
- Total gas fractions show little correlation with star formation rates.
- Most high-redshift dwarf galaxies are in recession, with star formation demand not meeting gas supply.

## Abstract

Using a series of high-resolution hydrodynamical simulations we show that during the rapid growth of high-redshift (z > 5) galaxies, reserves of molecular gas are consumed over a time-scale of 300Myr, almost independent of feedback scheme. We find that there exists no such simple relation for the total gas fractions of these galaxies, with little correlation between gas fractions and specific star formation rates. The bottleneck or limiting factor in the growth of early galaxies is in converting infalling gas to cold star-forming gas. Thus, we find that the majority of high redshift dwarf galaxies are effectively in recession, with demand (of star formation) never rising to meet supply (of gas), irrespective of the baryonic feedback physics modelled. We conclude that the basic assumption of self-regulation in galaxies - that they can adjust total gas consumption within a Hubble time - does not apply for the dwarf galaxies thought to be responsible for providing most UV photons to reionize the high redshift Universe. We demonstrate how this rapid molecular time-scale improves agreement between semi-analytic model predictions of the early Universe and observed stellar mass functions.