Reconstructing H i power spectrum with minimal parameters using the dark matter distribution beyond haloes

Abstract

ABSTRACT Intensity mapping of 21-cm line by several radio telescope experiments will probe the large-scale structure of the Universe in the post-reionization epoch. It requires a theoretical framework of neutral hydrogen (H i) clustering, such as modelling of H i power spectrum for baryon acoustic oscillations (BAO) analysis. We propose a new method for reconstructing the H i map from dark matter distribution using N-body simulations. Several studies attempt to compute the H i power spectrum with N-body simulations by pasting H i gas at the dark matter halo centre, assuming the relation between the halo and H i masses. On the other hand, the method proposed in this paper reproduces the H i power spectrum from simulated dark matter distribution truncated at specific scales from the halo centre. With this method, the slope of H i power spectrum is reproduced well at the BAO scales, k < 1 h/Mpc. Furthermore, we find the fluctuation of spin temperature, which is often ignored at the post-reionization epoch, alters the power spectrum of brightness temperature by at most 8 per cent in the power spectrum. Finally, we discuss how our method works by comparing the density profiles of H i and dark matter around the dark matter haloes.