Radiative feedback and the low efficiency of galaxy formation in low-mass haloes at high redshift

TL;DR

This paper models radiative feedback effects, including radiation pressure and photoionization, to explain the low star formation efficiency in low-mass galaxy progenitors at high redshift, aligning with observed stellar mass fractions.

Contribution

It introduces a comprehensive simulation approach incorporating radiation pressure, photoionization, and photoheating to better understand galaxy formation inefficiencies in low-mass halos.

Findings

Radiative feedback limits gas density and star formation rates in low-mass halos.

Simulations produce stellar mass fractions consistent with abundance matching.

Galaxies in low-mass halos exhibit extended structures with rising circular velocity profiles.

Abstract

Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today's galaxies. This inefficiency is necessary for reproducing the low stellar-to-virial mass fractions, suggested by current abundance matching models. A possible driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive stars. The effect of radiation pressure in cosmological, zoom-in galaxy formation simulations is modeled as a non-thermal pressure that acts only in dense and optically thick star-forming regions. We also include photoionization and photoheating by massive stars. The full photoionization of hydrogen reduces the radiative cooling in the $10^{4-4.5}$ K regime. The main effect of radiation pressure is to regulate and limit the high values of gas density and the amount of gas available for star formation. This maintains a low star formation rate of $\sim 1 \ {\rm M_\odot} \ {\rm yr}^{-1}$ in halos with masses about $10^{11} \ {M_\odot}$ at $z\simeq3$. Infrared trapping and photoionization/photoheating processes are secondary effects in this mass range. The galaxies residing in these low-mass halos contain only $\sim0.6\%$ of the total virial mass in stars, roughly consistent with abundance matching. Radiative feedback maintains an extended galaxy with a rising circular velocity profile.