Imprint of non-linear effects on HI intensity mapping on large scales

TL;DR

This paper derives the full third-order relativistic perturbation expression for HI brightness temperature and investigates how nonlinear effects influence large-scale intensity mapping power spectra.

Contribution

It provides the first comprehensive third-order relativistic perturbation expression for HI brightness temperature without plane-parallel approximation and analyzes nonlinear effects on large-scale power spectra.

Findings

Nonlinear bias and redshift space distortions modulate the power spectrum.

Mode coupling affects large-scale structure measurements.

Effective bias and shot noise influence large-scale modulation.

Abstract

Intensity mapping of the HI brightness temperature provides a unique way of tracing large-scale structures of the Universe up to the largest possible scales. This is achieved by using a low angular resolution radio telescopes to detect emission line from cosmic neutral Hydrogen in the post-reionization Universe. We use general relativistic perturbation theory techniques to derive for the first time the full expression for the HI brightness temperature up to third order in perturbation theory without making any plane-parallel approximation. We use this result and the renormalization prescription for biased tracers to study the impact of nonlinear effects on the power spectrum of HI brightness temperature both in real and redshift space. We show how mode coupling at nonlinear order due to nonlinear bias parameters and redshift space distortion terms modulate the power spectrum on large scales. The large scale modulation may be understood to be due to the effective bias parameter and effective shot noise.