2019ApJ...875...67M

We present new constraints on parameters of cosmic dawn and the epoch of reionization derived from the EDGES High-Band spectrum (90-190 MHz). The parameters are probed by evaluating global 21 cm signals generated with the recently developed Global21cm tool. This tool uses neural networks trained and tested on ∼30,000 spectra produced with semi-numerical simulations that assume the standard thermal evolution of the cosmic microwave background and the intergalactic medium. From our analysis, we constrain at 68% (1) the minimum virial circular velocity of star-forming halos to V_c < 19.3 km s^–1, (2) the X-ray heating efficiency of early sources to f_X > 0.0042, and (3) the low-energy cutoff of the X-ray spectral energy distribution to ν_min < 2.3 keV. We also constrain the star formation efficiency (f_*), the electron scattering optical depth (τ_e), and the mean-free path of ionizing photons (R_mfp). We recompute the constraints after incorporating into the analysis four estimates for the neutral hydrogen fraction from high-z quasars and galaxies, and a prior on τ_e from Planck 2018. The largest impact of the external observations is on the parameters that most directly characterize reionization. Specifically, we derive the combined 68% constraints τ_e < 0.063 and R_mfp > 27.5 Mpc. The external observations also have a significant effect on V_c due to its degeneracy with τ_e, while the constraints on f_*, f_X, and ν_min, remain primarily determined by EDGES.