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

Abstract

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 ($\zeta$), (2) minimum halo virial temperature hosting efficient star-forming galaxies ($T_{\mathrm{vir}}^{\min }$), (3) integrated soft-band X-ray luminosity ($L_{\mathrm{X}<2\mathrm{keV}}/\mathrm{SFR}$), and (4) minimum X-ray energy escaping the first galaxies ($E_0$), corresponding to a typical H$\mathrm{I}$ column density for attenuation through the interstellar medium. The High-Band spectrum disfavors high values of $T_{\mathrm{vir}}^{\min }$ and $\zeta$, which correspond to signals with late absorption troughs and sharp reionization transitions. It also disfavors intermediate values of $L_{\mathrm{X}<2\mathrm{keV}}/\mathrm{SFR}$, which produce relatively deep and narrow troughs within the band. Specifically, we rule out $39.4<{\log }_{10}\left(L_{\mathrm{X}<2\mathrm{keV}}/\mathrm{SFR}\right)<39.8$ ($95\%$ 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 $\zeta$ and $T_{\mathrm{vir}}^{\min }$ than that reported in Greig & Mesinger (2017a) using the Planck and quasar constraints alone. Our main result in this combined analysis is the estimate $4.5$~$\le {\log }_{10}\left(T_{\mathrm{vir}}^{\min }/\mathrm{K}\right)\le$~$5.7$ ($95\%$ C.L.). We leave for future work the evaluation of $21$~cm models using simultaneously data from EDGES Low- and High-Band.

Accepted in ApJ