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

Studies of the formation of the first stars have established that they formed in small haloes of ~105-106M⊙ 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 ~ 15 and much more massive haloes came to dominate star formation. However, metal enrichment from the first stars may have allowed the smaller haloes to continue to form stars. In this Letter, we explore the possible effect of star formation inmetal-rich low-mass haloes on the redshifted 21-cm signal of neutral hydrogen from z = 6 to 40. These haloes 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 haloes was more efficient than suggested by current simulations. We show that upcoming radio telescopes can easily distinguish among various possible scenarios.