Results from EDGES High-Band. III. New Constraints on Parameters of the Early Universe

• Published in: The Astrophysical journal Vol. 875; no. 1; pp. 67 - 83
• Main Authors: Monsalve, Raul A., Fialkov, Anastasia, Bowman, Judd D., Rogers, Alan E. E., Mozdzen, Thomas J., Cohen, Aviad, Barkana, Rennan, Mahesh, Nivedita
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10.04.2019; IOP Publishing
• Subjects: Astrophysics; Big Bang theory; Computer simulation; Cosmic microwave background; cosmology: observations; early universe; Galaxies; galaxies: high-redshift; Halos; Hydrogen; Intergalactic media; Ionization; methods: data analysis; Neural networks; Numerical simulations; Optical analysis; Optical thickness; Parameters; Quasars; Spectral energy distribution; Star & galaxy formation; Star formation; Thermal evolution; X ray spectra
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab07be

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 Vc < 19.3 km s−1, (2) the X-ray heating efficiency of early sources to fX > 0.0042, and (3) the low-energy cutoff of the X-ray spectral energy distribution to min < 2.3 keV. We also constrain the star formation efficiency (f*), the electron scattering optical depth (τe), and the mean-free path of ionizing photons (Rmfp). 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 τe 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 τe < 0.063 and Rmfp > 27.5 Mpc. The external observations also have a significant effect on Vc due to its degeneracy with τe, while the constraints on f*, fX, and min, remain primarily determined by EDGES.