The imprint of the relative velocity between baryons and dark matter on the 21-cm signal from reionization

TL;DR

This paper investigates how the relative velocity between baryons and dark matter influences the 21-cm signal during reionization, revealing that effects depend on star formation cooling scenarios and can alter reionization timing and power spectrum.

Contribution

It demonstrates the dependence of baryon streaming effects on star formation cooling models and quantifies their impact on reionization timing and 21-cm power spectrum predictions.

Findings

No major impact for atomic hydrogen cooling scenarios.

Reionization is delayed by about Δz ≈ 2 with molecular hydrogen cooling.

Increased large-scale power in the 21-cm signal during reionization.

Abstract

The post-recombination streaming of baryons through dark matter keeps baryons out of low mass (<10^6 solar masses) halos coherently on scales of a few comoving Mpc. It has been argued that this will have a large impact on the 21-cm signal before and after reionization, as it raises the minimum mass required to form ionizing sources. Using a semi-numerical code, we show that the impact of the baryon streaming effect on the 21-cm signal during reionization (redshifts z approximately 7-20) depends strongly on the cooling scenario assumed for star formation, and the corresponding virial temperature or mass at which stars form. For the canonical case of atomic hydrogen cooling at 10^4 Kelvin, the minimum mass for star formation is well above the mass of halos that are affected by the baryon streaming and there are no major changes to existing predictions. For the case of molecular hydrogen cooling, we find that reionization is delayed by a change in redshift of approximately 2 and that more relative power is found in large modes at a given ionization fraction. However, the delay in reionization is degenerate with astrophysical assumptions, such as the production rate of UV photons by stars.