Galaxy formation in the Planck Millennium: the atomic hydrogen content of dark matter halos

TL;DR

This paper recalibrates a galaxy formation model using the Planck Millennium simulation to predict the atomic hydrogen content in dark matter halos, revealing key relations and their evolution with redshift.

Contribution

It provides updated predictions for the HI content in halos using a large simulation and minimal parameter adjustments, enhancing understanding of HI distribution for cosmological studies.

Findings

HI mass-halo mass relation shows a break at ~3x10^11 M_sun due to AGN heating.

Below this mass, HI is dominated by central galaxies; above, by satellites.

HI bias exhibits scale dependence increasing with redshift.

Abstract

We present recalibrations of the GALFORM semi-analytical model of galaxy formation in a new N-body simulation with the Planck cosmology. The Planck Millennium simulation uses more than 128 billion particles to resolve the matter distribution in a cube of $800$ Mpc on a side, which contains more than 77 million dark matter haloes with mass greater than $2.12 \times 10^{9} h^{-1} {\rm M_{\odot}}$ at the present day. Only minor changes to a very small number of model parameters are required in the recalibration. We present predictions for the atomic hydrogen content (HI) of dark matter halos, which is a key input into the calculation of the HI intensity mapping signal expected from the large-scale structure of the Universe. We find that the HI mass $-$ halo mass relation displays a clear break at the halo mass above which AGN heating suppresses gas cooling, $\approx 3 \times 10^{11} h^{-1} M_{\rm \odot}$. Below this halo mass, the HI content of haloes is dominated by the central galaxy; above this mass it is the combined HI content of satellites that prevails. We find that the HI mass - halo mass relation changes little with redshift up to $z=3$. The bias of HI sources shows a scale dependence that gets more pronounced with increasing redshift.