Halo mass functions at high redshift

TL;DR

This study compares semi-analytic and N-body halo mass functions at high redshift using simulations, finding discrepancies are small and unlikely to explain tensions between JWST observations and standard cosmological models.

Contribution

It provides a detailed comparison of halo mass functions from different methods at high redshift, assessing their impact on observational tensions.

Findings

Discrepancies between methods are less than a factor of 2 at z~10.

Differences are not the main source of tension in high-redshift galaxy observations.

N-body and semi-analytic models are broadly consistent within current observational uncertainties.

Abstract

Recent JWST observations of very early galaxies, at $\rm{z \gtrsim 10}$, have led to claims that tension exists between the sizes and luminosities of high-redshift galaxies and what is predicted by standard $\Lambda$CDM models. Here we use the adaptive mesh refinement code $\texttt{Enzo}$ and the N-body smoothed particle hydrodynamics code $\texttt{SWIFT}$ to compare (semi-)analytic halo mass functions against the results of direct N-body models at high redshift. In particular, our goal is to investigate the variance between standard halo mass functions derived from (semi-)analytic formulations and N-body calculations and to determine what role any discrepancy may play in driving tensions between observations and theory. We find that the difference between direct N-body calculations and (semi-) analytic halo mass function fits is less than a factor of 2 (at $\rm{z \sim 10}$) within the mass range of galaxies currently being observed by JWST, and is therefore not a dominant source of error when comparing theory and observation at high redshift.