The impact of Lyman-$\alpha$ emission line heating and cooling on the cosmic dawn 21-cm signal

TL;DR

This paper explores how enhanced Lyman-alpha emission from early galaxies could significantly alter the 21-cm signal during cosmic dawn, affecting its temperature and detectability.

Contribution

It introduces a model considering Lyman-alpha line emission effects on the 21-cm signal, highlighting potential heating or cooling mechanisms in the early universe.

Findings

Possible 21-cm signals near -500 mK at redshifts 15-25

Lyman-alpha photons can heat or cool intergalactic gas

Signatures similar to EDGES detection may occur

Abstract

Allowing for enhanced Ly$\alpha$ photon line emission from Population III dominated stellar systems in the first forming galaxies, we show the 21-cm cosmic dawn signal at $10<z<30$ may substantially differ from standard scenarios. Energy transfer by Ly$\alpha$ photons emerging from galaxies may heat intergalactic gas if HII regions within galaxies are recombination bound, or cool the gas faster than by adiabatic expansion if reddened by winds internal to the haloes. In some cases, differential 21-cm antenna temperatures near $-500$ mK may be achieved at $15<z<25$, similar to the signature detected by the EDGES 21-cm cosmic dawn experiment.