A halo model for cosmological neutral hydrogen : abundances and clustering

Abstract

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