Modeling the Nonlinear Power Spectrum in Low-redshift H i Intensity Mapping

Abstract

Abstract Neutral Hydrogen (H i) serves as a competitive tracer of the large scale structures, especially with the advent of more Intensity Mapping H i surveys. In this work, we present a simulation-based framework to forecast the H i power spectrum on non-linear scales (k ≳ 1 Mpc−1), as measured by interferometer arrays like MeerKAT in the low-redshift (z ≤ 1.0) universe. Building on a galaxy-based H i mock catalog, we meticulously consider various factors, including the emission line profiles of H i discs and some observational settings, and explore their impacts on the H i power spectrum. We find that the H i power spectrum is relatively insensitive to the profile shape of H i emission line at these scales, while showing a strong correlation with the profile width. We propose an empirical model to simulate the emission line profile width for each H i source. The resulting H i power spectrum is consistent with the results from the IllustrisTNG hydrodynamical simulation and follows the trend of the measurements obtained by MeerKAT at z ≈ 0.44, though with a significantly lower amplitude. We demonstrate how the HI abundance ΩHI and the amplitude parameter in our width model can be constrained with the MeerKAT measurements, though a strong degeneracy is uncovered. Our work shows the potential to constrain statistical properties of HI emission line profiles with future HI Intensity Mapping experiments.