Modeling The Large Scale Bias of Neutral Hydrogen

TL;DR

This paper develops analytical models to estimate the large scale bias of neutral hydrogen over cosmic time, showing strong evolution with redshift and consistency with simulation data, with minimal impact on power spectrum measurements.

Contribution

It introduces a simple non-parametric model linking halo mass to HI mass and explores bias evolution with redshift, validated against Millennium Simulation data.

Findings

Bias terms evolve strongly with redshift

Model predictions align with Millennium Simulation measurements

Bias evolution has limited effect on HI power spectrum measurement

Abstract

We present new analytical estimates of the large scale bias of neutral hydrogen (HI). We use a simple, non-parametric model which monotonically relates the total mass of a halo M_tot with its HI mass M_HI at zero redshift; for earlier times we assume limiting models for the HI density evolution consistent with the data presently available, as well as two main scenarios for the evolution of our M_HI - 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 HI power spectrum.