# Efficacy of early stellar feedback in low gas surface density environments

## TL;DR

This study uses high-resolution radiation hydrodynamic simulations to evaluate how early stellar feedback processes like radiation and supernovae influence star formation and outflows in low gas surface density galaxies, showing radiation significantly reduces star formation and enhances outflows.

## Contribution

It provides new insights into the relative roles of radiation feedback and supernovae in low-density environments, highlighting the importance of photoheating over radiation pressure.

## Key findings

- Radiation fields halve star formation rates and increase gas depletion times.
- Coupled radiation and supernova feedback drive outflows with 10 times more mass and energy.
- Photoheating expands high-density regions, boosting supernova momentum output.

## Abstract

We present a suite of high resolution radiation hydrodynamic simulations of a small patch ($1 \ {\rm kpc}^2$) of the inter-stellar medium (ISM) performed with Arepo-RT, with the aim to quantify the efficacy of various feedback processes like supernovae explosions (SNe), photoheating and radiation pressure in low gas surface density galaxies ($\Sigma_{\rm gas} \simeq 10 \ {\rm M}_\odot \ {\rm pc}^{-2}$). We show that radiation fields decrease the star formation rate and therefore the total stellar mass formed by a factor of $\sim 2$. This increases the gas depletion timescale and brings the simulated Kennicutt-Schmidt relation closer to the observational estimates. Radiation feedback coupled with SNe is more efficient at driving outflows with the mass and energy loading increasing by a factor of $\sim 10$. This increase is mainly driven by the additional entrainment of medium density ($10^{-2} \leq n< 1 \ {\rm cm}^{-3}$), warm ($300 \ {\rm K}\leq T<8000 \ {\rm K}$) material. Therefore including radiation fields tends to launch colder, denser and higher mass and energy loaded outflows. This is because photoheating of the high density gas around a newly formed star over-pressurises the region, causing it to expand. This reduces the ambient density in which the SNe explode by a factor of $10-100$ which in turn increases their momentum output by a factor of $\sim 1.5-2.5$. Finally, we note that in these low gas surface density environments, radiation fields primarily impact the ISM via photoheating and radiation pressure has only a minimal role in regulating star formation.