Impact of dark matter-baryon relative velocity on the 21cm forest

TL;DR

This paper investigates how the relative velocity between dark matter and baryons influences the 21cm forest signals, revealing a significant suppression in absorption line abundance due to small-scale matter power spectrum effects.

Contribution

It demonstrates the impact of DM-baryon relative velocity on 21cm forest signals and quantifies the suppression of absorption lines caused by small-scale power spectrum modifications.

Findings

21cm forest signals are sensitive to DM-baryon streaming velocities.

The matter power spectrum is suppressed at scales relevant to 21cm signals.

Absorption line abundance can decrease by more than a factor of two.

Abstract

We study the effect of the relative velocity between the dark matter (DM) and the baryon on the 21cm forest signals. The DM-baryon relative velocity arises due to their different evolutions before the baryon-photon decoupling epoch and it gives an additional anisotropic pressure that can suppress the perturbation growth. It is intriguing that the scales $k\sim {\cal O}(10\sim 10^3)h/\mathrm{Mpc}$ at which the matter power spectrum is affected by such a streaming velocity turns out to be the scale at which the 21cm forest signal is sensitive to. We demonstrate that the 21cm absorption line abundance can decrease by more than a factor of a few due to the small-scale matter power spectrum suppression caused by the DM-baryon relative velocity.