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We investigate the effects of Population III (Pop III) stars and theirremnants on the cosmological 21-cm global signal. By combining a semi-analyticmodel of Pop III star formation with a global 21-cm simulation code, weinvestigate how X-ray and radio emission from accreting Pop III black holes mayaffect both the timing and depth of the 21-cm absorption feature that followsthe initial onset of star formation during the Cosmic Dawn. We compare ourresults to the findings of the EDGES experiment, which has reported the firstdetection of a cosmic 21-cm signal. In general, we find that our fiducial PopIII models, which have peak star formation rate densities of $\sim 10^{-4}$M$_\odot$ yr$^{-1}$ Mpc$^{-3}$ between $z \sim 10$ and $z \sim 15$, are able tomatch the timing of the EDGES signal quite well, in contrast to models thatignore Pop III stars. To match the unexpectedly large depth of the EDGES signalwithout recourse to exotic physics, we vary the parameters of emission fromaccreting black holes (formed as Pop III remnants) including the intrinsicstrength of X-ray and radio emission as well as the local column density ofneutral gas. We find that models with strong radio emission and relatively weakX-ray emission can self-consistently match the EDGES signal, though thissolution requires fine-tuning. We are only able to produce signals with sharpfeatures similar to the EDGES signal if the Pop~III IMF is peaked narrowlyaround $140 \, M_\odot$.

The Effects of Population III X-ray and Radio Backgrounds on the Cosmological 21-cm Signal