Results from EDGES High-Band: II. Constraints on Parameters of Early Galaxies

We use the sky-average spectrum measured by EDGES High-Band (90-190 MHz) to constrain parameters of early galaxies independent of the absorption feature at 78~MHz reported by Bowman et al. (2018). These parameters represent traditional models of cosmic dawn and the epoch of reionization produced with the 21cmFAST simulation code (Mesinger & Furlanetto 2007, Mesinger et al. 2011). The parameters considered are: (1) the UV ionizing efficiency (ζ), (2) minimum halo virial temperature hosting efficient star-forming galaxies (T^{rm min}_{rm vir}), (3) integrated soft-band X-ray luminosity (L_{rm X,<,2,keV}/{rm SFR}), and (4) minimum X-ray energy escaping the first galaxies (E_{0}), corresponding to a typical H{rm scriptstyle I} column density for attenuation through the interstellar medium. The High-Band spectrum disfavors high values of T^{rm min}_{rm vir} and ζ, which correspond to signals with late absorption troughs and sharp reionization transitions. It also disfavors intermediate values of L_{rm X,<,2,keV}/{rm SFR}, which produce relatively deep and narrow troughs within the band. Specifically, we rule out 39.4<log_{10}left(L_{rm X,<,2,keV}/{rm SFR}right)<39.8 (95% C.L.). We then combine the EDGES High-Band data with constraints on the electron scattering optical depth from Planck and the hydrogen neutral fraction from high-z quasars. This produces a lower degeneracy between ζ and T^{rm min}_{rm vir} than that reported in Greig & Mesinger (2017a) using the Planck and quasar constraints alone. Our main result in this combined analysis is the estimate 4.5~leq log_{10}left(T^{rm min}_{rm vir}/rm Kright)leq~5.7 (95% C.L.). We leave for future work the evaluation of 21~cm models using simultaneously data from EDGES Low- and High-Band.