Modeling the Large-Scale Bias of Neutral Hydrogen

We present new analytical estimates of the large-scale bias of neutral hydrogen (H i ). We use a simple, non-parametric model which monotonically relates the total mass of a halo M tot with its H i mass M H i at zero redshift; for earlier times we assume limiting models for the Ω H i evolution consistent with the data presently available, as well as two main scenarios for the evolution of our M H i – M tot relation. We find that both the linear and the first nonlinear bias terms exhibit a strong evolution with redshift, regardless of the specific limiting model assumed for the H i density over time. These analytical predictions are then shown to be consistent with measurements performed on the Millennium Simulation. Additionally, we show that this strong bias evolution does not sensibly affect the measurement of the H i power spectrum.