# Simulating the effect of photoheating feedback during reionization

## TL;DR

This study uses advanced radiation hydrodynamic simulations to assess how photoheating during reionization influences galaxy formation, finding it less impactful than previously thought and not leaving clear observable signatures.

## Contribution

It provides a self-consistent simulation framework showing that photoheating feedback is weaker and less observable than earlier models suggested.

## Key findings

- Photoheating suppresses star formation mainly in halos below ~10^{8.4} M_sun.
- Uniform UV background causes earlier star formation suppression than the fiducial model.
- Photoheating alone cannot significantly quench star formation in halos above ~10^9 M_sun.

## Abstract

We present self-consistent radiation hydrodynamic simulations of hydrogen reionization performed with Arepo-RT complemented by a state-of-the-art galaxy formation model. We examine how photoheating feedback, due to reionization, shapes the galaxies properties. Our fiducial model completes reionization by $z\approx6$ and matches observations of the Ly$\alpha$ forest, the CMB electron scattering optical depth, the high-redshift UV luminosity function, and stellar mass function. Contrary to previous works, photoheating suppresses star formation rates by more than $50\%$ only in halos less massive than $\sim10^{8.4}\ M_\odot$ ($\sim10^{8.8}\ M_\odot$) at $z=6$ $(z=5)$, suggesting inefficient photoheating feedback from photons within galaxies. The use of a uniform UV background that heats up the gas at $z\approx10.7$ generates an earlier onset of suppression of star formation compared to our fiducial model. This discrepancy can be mitigated by adopting a UV background model with a more realistic reionization history. In the absence of stellar feedback, photoheating alone is only able to quench halos less massive than $\sim10^9\ M_\odot$ at $z\gtrsim5$, implying that photoheating feedback is sub-dominant in regulating star formation. In addition, stellar feedback, implemented as a non-local galactic wind scheme in the simulations, weakens the strength of photoheating feedback by reducing the amount of stellar sources. Most importantly, photoheating does not leave observable imprints in the UV luminosity function, stellar mass function, or the cosmic star formation rate density. The feasibility of using these observables to detect imprints of reionization therefore requires further investigation.