2015MNRAS.447.3745P

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