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.
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