Theoretical and observational constraints on the H i intensity power spectrum

Abstract

Mapping of the neutral hydrogen (H I) 21-cm intensity fluctuations across redshifts promises a novel and powerful probe of cosmology. The neutral hydrogen gas mass density H I and bias parameter b H I are key astrophysical inputs to the H I intensity fluctuation power spectrum. We compile the latest theoretical and observational constraints on H I and b H I at various redshifts in the post-reionization universe. Constraints are incorporated from galaxy surveys, H I intensity mapping experiments, damped Lyman system observations, theoretical prescriptions for assigning H I to dark matter haloes and the results of numerical simulations. Using a minimum variance interpolation scheme, we obtain the predicted uncertainties on the H I intensity fluctuation power spectrum across redshifts 0-3.5 for three different confidence scenarios. We provide a convenient tabular form for the interpolated values of H I , b H I and the H I power spectrum amplitude and their uncertainties. We discuss the consequences for the measurement of the power spectrum by current and future intensity mapping experiments.