Precise Measurement of the Reionization Optical Depth from The Global 21-cm Signal Accounting for Cosmic Heating

Abstract

As a result of our limited data on reionization, the total optical depth for electron scattering, $\tau$, limits precision measurements of cosmological parameters from the Cosmic Microwave Background (CMB). It was recently shown that the predicted 21-cm signal of neutral hydrogen contains enough information to reconstruct $\tau$ with sub-percent accuracy, assuming that the neutral gas was much hotter than the CMB throughout the entire epoch of reionization. Here we relax this assumption and use the global 21-cm signal alone to extract $\tau$ for realistic X-ray heating scenarios. We test our model-independent approach using mock data for a wide range of ionization and heating histories and show that an accurate measurement of the reionization optical depth at a sub-percent level is possible in most of the considered scenarios even when heating is not saturated during the epoch of reionization, assuming that the foregrounds are mitigated. However, we find that in cases where heating sources had hard X-ray spectra and their luminosity was close to or lower than what is predicted based on low-redshift observations, the global 21-cm signal alone is not a good tracer of the reionization history.

Accepted for publication, ApJ; 9 pages, 5 figures, 1 table

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• Results from EDGES High-Band: I. Constraints on Phenomenological Models for the Global $21$ cm Signal
• SARAS 2 constraints on global 21-cm signals from the Epoch of Reionization
• Calibration of the EDGES High-Band Receiver to Observe the Global 21-cm Signature from the Epoch of Reionization
• Alleviating the Tension in the Cosmic Microwave Background using Planck-Scale Physics
• Illuminating the dark ages: Cosmic backgrounds from accretion onto primordial black hole dark matter
• Charting the Parameter Space of the 21-cm Power Spectrum
• The AARTFAAC Cosmic Explorer: observations of the 21-cm power spectrum in the EDGES absorption trough
• Constraining the CMB Optical Depth Through the Dispersion Measure of Cosmological Radio Transients
• 21cmfish: Fisher-matrix framework for fast parameter forecasts from the cosmic 21-cm signal
• Influence of ~7 keV sterile neutrino dark matter on the process of reionization
• Cosmic tango between the very small and the very large: Addressing CMB anomalies through Loop Quantum Cosmology
• Nonlinear reconstruction of 21cm global signal from 21cm power spectrum with artificial neural networks