The Breakdown Scale of H I Bias Linearity
January 2021 • 2021ApJ...907....4W
Abstract • The 21 cm intensity mapping experiments promise to obtain the large-scale distribution of H I gas at the post-reionization epoch. In order to reveal the underlying matter density fluctuations from the H I mapping, it is important to understand how H I gas traces the matter density distribution. Both nonlinear halo clustering and nonlinear effects modulating H I gas in halos may determine the scale below which the H I bias deviates from linearity. We employ three approaches to generate the mock H I density from a large-scale N-body simulation at low redshifts, and demonstrate that the assumption of H I linearity is valid at the scale corresponding to the first peak of baryon acoustic oscillations, but breaks down at k ≳ 0.1 h Mpc-1. The nonlinear effects of halo clustering and H I content modulation counteract each other at small scales, and their competition results in a model-dependent "sweet-spot" redshift near z = 1, where the H I bias is scale-independent down to small scales. We also find that the linear H I bias scales approximately linearly with redshift for z ≤ 3.
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