NeutralUniverseMachine: Predictions of HI gas in Different Theoretical Models

TL;DR

This paper compares various theoretical models' predictions of HI gas distribution and evolution, highlighting their agreement at low redshift and divergence at higher redshifts, with implications for understanding galaxy formation.

Contribution

It provides a comprehensive comparison of hydro-dynamical, semi-analytic, and empirical models' predictions of HI gas properties across redshifts, revealing key differences and their origins.

Findings

All models agree with observed HIMF at z~0.

NUM model matches observed HIMF well at z=1.

Differences at higher redshifts are mainly due to AGN feedback implementations.

Abstract

We investigate the distribution and evolution of HI gas in different theoretical models, including hydro-dynamical simulations (Illustris-TNG and SIMBA), semi-analytic models (GAEA), and the empirical models ( NeutralUniverseMachine; NUM). By comparing model predictions for the HI mass function (HIMF), HI-halo and HI-stellar mass relations, conditional HI mass function (CHIMF) and the halo occupation distribution (HOD) of HI-selected galaxies, we find that all models show reasonable agreement with the observed HIMF at $z\sim0$, but the differences become much larger at higher redshifts of $z=1$ and $z=2$. The HIMF of NUM shows remarkable agreement with the observation at $z=1$, whereas other models predict much lower amplitudes of HIMF at the high-mass end. Comparisons of CHIMF distributions indicate that the HIMF is dominated by halos of $10< \log(M_{\rm vir}/M_\odot) <11$ and $11< \log(M_{\rm vir}/M_\odot)<12$ at the low- and high-mass ends, respectively. From the HI HODs of central galaxies, we find that TNG100 overpredicts the number of central galaxies with high $M_{\rm HI}$ in massive halos and GAEA shows a very strong depletion of HI gas in quenched centrals of massive halos. The main cause of the differences is the AGN feedback mechanisms implemented in different models.