A halo model for cosmological neutral hydrogen: abundances and clustering

TL;DR

This paper develops a halo model to describe the abundance and clustering of neutral hydrogen across different redshifts, fitting diverse observational data with a comprehensive approach.

Contribution

It introduces a unified halo model framework that accurately fits HI observations from low to high redshifts, including clustering, column density, and DLA data.

Findings

A radial exponential profile fits low-redshift HI data well.

The model matches high-redshift DLA observations with redshift evolution.

Predictions agree with observed HI surface density and DLA impact parameters.

Abstract

We extend the results of previous analyses towards constraining the abundance and clustering of post-reionization ($z \sim 0-5$) neutral hydrogen (HI) systems using a halo model framework. We work with a comprehensive HI dataset including the small-scale clustering, column density and mass function of HI galaxies at low redshifts, intensity mapping measurements at intermediate redshifts and the UV/optical observations of Damped Lyman Alpha (DLA) systems at higher redshifts. We use a Markov Chain Monte Carlo (MCMC) approach to constrain the parameters of the best-fitting models, both for the HI-halo mass relation and the HI radial density profile. We find that a radial exponential profile results in a good fit to the low-redshift HI observations, including the clustering and the column density distribution. The form of the profile is also found to match the high-redshift DLA observations, when used in combination with a three-parameter HI-halo mass relation and a redshift evolution in the HI concentration. The halo model predictions are in good agreement with the observed HI surface density profiles of low-redshift galaxies, and the general trends in the the impact parameter and covering fraction observations of high-redshift DLAs. We provide convenient tables summarizing the best-fit halo model predictions.