The Halo Occupation Distribution of HI from 21cm Intensity Mapping at Moderate Redshifts

Abstract

The spatial clustering properties of HI galaxies can be studied using the formalism of the halo occupation distribution (HOD). The resulting parameter constraints describe properties like gas richness verses environment. Unfortunately, clustering studies based on individual HI galaxies will be restricted to the local Universe for the foreseeable future, even with the deepest HI surveys. Here we discuss how clustering studies of the HI HOD could be extended to moderate redshift, through observations of fluctuations in the combined 21cm intensity of unresolved galaxies. In particular we make an analytic estimate for the clustering of HI in the HOD. Our joint goals are to estimate i) the amplitude of the signal, and ii) the sensitivity of telescopes like the Australian SKA Pathfinder to HOD parameters. We find that the power spectrum of redshifted 21cm intensity could be used to study the distribution of HI within dark matter halos at z>0.5 where individual galaxies cannot be detected. In addition to the HOD of HI, the amplitude of the 21cm power spectrum would also yield estimates of the cosmic HI content at epochs between the local Universe, and redshifts probed by damped Ly-alpha absorbers.

10 pages, 5 figures. Submitted to MNRAS

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• Constraints on the evolution of the relationship between HI mass and halo mass in the last 12 Gyr
• Detecting neutral hydrogen in emission at redshift z ~ 1
• The spatial distribution of neutral hydrogen as traced by low HI mass galaxies
• A direct detection of neutral hydrogen intensity mapping on Mpc scales at $z\approx 0.32$ and $z\approx 0.44$
• On the role of feedback in shaping the cosmic abundance and clustering of neutral atomic hydrogen in galaxies
• Halo models of HI selected galaxies
• A Multi-messenger view of Cosmic Dawn: Conquering the Final Frontier
• The power spectrum of galaxies from large to small scales: a line-intensity mapping perspective
• Prospects of detecting HI using redshifted 21 cm radiation at z ~ 3