Constraining the Minimum Mass of High-Redshift Galaxies and Their Contribution to the Ionization State of the IGM

TL;DR

This study models high-redshift galaxy observations to constrain the minimum halo mass necessary for galaxy formation and assesses their role in ionizing the intergalactic medium, highlighting the importance of faint galaxies.

Contribution

It introduces a hierarchical galaxy formation model fitting observed luminosity functions to determine the minimum halo mass at high redshift, impacting ionizing photon estimates.

Findings

Minimum halo mass for galaxy formation is about 10^{9.4} solar masses.

Faint, undetected galaxies significantly influence the ionizing photon budget.

Future JWST observations are crucial for confirming the contribution of faint galaxies.

Abstract

We model the latest HST WFPC3/IR observations of > 100 galaxies at redshifts z=7-8 in terms of a hierarchical galaxy formation model with starburst activity. Our model provides a distribution of UV luminosities per dark matter halo of a given mass and a natural explanation for the fraction of halos hosting galaxies. The observed luminosity function is best fit with a minimum halo mass per galaxy of 10^{9.4+0.3-0.9} Msun, corresponding to a virial temperature of 10^{4.9+0.2-0.7} K. Extrapolating to faint, undetected galaxies, the total production rate of ionizing radiation depends critically on this minimum mass. Future measurements with JWST should determine whether the entire galaxy population can comfortably account for the UV background required to keep the intergalactic medium ionized.