The impact of Lyα emission line heating and cooling on the cosmic dawn 21-cm signal.

Allowing for enhanced Lyα 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 Lyα photons emerging from galaxies may heat intergalactic gas if H  ii 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 extreme 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. [ABSTRACT FROM AUTHOR]