The 21-cm BAO signature of enriched low-mass galaxies during cosmic reionization

TL;DR

This paper investigates how metal enrichment in low-mass halos during cosmic reionization could produce a detectable 21-cm BAO signature, offering insights into early star formation and galaxy evolution.

Contribution

It explores the impact of metal-rich low-mass halos on the 21-cm signal, highlighting a potential observable BAO feature linked to early galaxy formation.

Findings

Metal enrichment can produce a strong 21-cm BAO signature.

Upcoming radio telescopes can distinguish different star formation scenarios.

Star formation in small halos may have been more efficient than current models suggest.

Abstract

Studies of the formation of the first stars have established that they formed in small halos of $\sim 10^5 - 10^6 M_{\odot}$ via molecular hydrogen cooling. Since a low level of ultraviolet radiation from stars suffices to dissociate molecular hydrogen, under the usually-assumed scenario this primordial mode of star formation ended by redshift $z \sim 15$ and much more massive halos came to dominate star formation. However, metal enrichment from the first stars may have allowed the smaller halos to continue to form stars. In this Letter we explore the possible effect of star formation in metal-rich low-mass halos on the redshifted 21-cm signal of neutral hydrogen from $z = 6-40$. These halos are significantly affected by the supersonic streaming velocity, with its characteristic baryon acoustic oscillation (BAO) signature. Thus, enrichment of low-mass galaxies can produce a strong signature in the 21-cm power spectrum over a wide range of redshifts, especially if star formation in the small halos was more efficient than suggested by current simulations. We show that upcoming radio telescopes can easily distinguish among various possible scenarios.