Estimation of cosmological prameters from neutral hydrogen observations of the post-reionization epoch

Abstract

The emission from neutral hydrogen (HI) clouds in the post-reionization era (z<=6), too faint to be individually detected, is present as a diffuse background in all low frequency radio observations below 1420 MHz. The angular and frequency fluctuations of this radiation (~1 mK) are an important future probe of the large-scale structures in the Universe. We show that such observations are a very effective probe of the background cosmological model and the perturbed Universe. In our study we focus on the possibility of determining the redshift-space distortion parameter beta, coordinate distance rnu, and its derivative with redshift rnu[prime]. Using reasonable estimates for the observational uncertainties and configurations representative of the ongoing and upcoming radio interferometers, we predict parameter estimation at a precision comparable with supernova Ia observations and galaxy redshift surveys, across a wide range in redshift that is only partially accessed by other probes. Future HI observations of the post-reionization era present a new technique, complementing several existing ones, to probe the expansion history and to elucidate the nature of the dark energy.