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

Abstract

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 $\sim 30,000$ 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 $V_{\mathrm{c}}<19.3$ km s${}^{-1}$, (2) the X-ray heating efficiency of early sources to $f_{\mathrm{X}}>0.0042$, and (3) the low-energy cutoff of the X-ray spectral energy distribution to ${\nu }_{\min }<2.3$ keV. We also constrain the star-formation efficiency ($f_{\ast }$), the electron scattering optical depth (${\tau }_{\mathrm{e}}$), and the mean-free path of ionizing photons ($R_{\mathrm{mfp}}$). We re-compute the constraints after incorporating into the analysis four estimates for the neutral hydrogen fraction from high-$z$ quasars and galaxies, and a prior on ${\tau }_{\mathrm{e}}$ 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 ${\tau }_{\mathrm{e}}<0.063$ and $R_{\mathrm{mfp}}>27.5$ Mpc. The external observations also have a significant effect on $V_{\mathrm{c}}$ due to its degeneracy with ${\tau }_{\mathrm{e}}$, while the constraints on $f_{\ast }$, $f_{\mathrm{X}}$, and ${\nu }_{\min }$, remain primarily determined by EDGES.

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Cited by in corpus (3)

• Constraining the intergalactic medium at $z\approx$ 9.1 using LOFAR Epoch of Reionization observations
• The 21 cm-kSZ-kSZ Bispectrum during the Epoch of Reionization
• Statistical Detection of IGM Structures during Cosmic Reionization using Absorption of the Redshifted 21 cm line by HI against Compact Background Radio Sources