Results from EDGES High-Band: I. Constraints on Phenomenological Models for the Global $21$ cm Signal

Abstract

We report constraints on the global $21$ cm signal due to neutral hydrogen at redshifts $14.8\ge z\ge 6.5$. We derive our constraints from low foreground observations of the average sky brightness spectrum conducted with the EDGES High-Band instrument between September $7$ and October $26$, $2015$. Observations were calibrated by accounting for the effects of antenna beam chromaticity, antenna and ground losses, signal reflections, and receiver parameters. We evaluate the consistency between the spectrum and phenomenological models for the global $21$ cm signal. For tanh-based representations of the ionization history during the epoch of reionization, we rule out, at $\ge 2\sigma$ significance, models with duration of up to $\Delta z=1$ at $z\approx 8.5$ and higher than $\Delta z=0.4$ across most of the observed redshift range under the usual assumption that the $21$ cm spin temperature is much larger than the temperature of the cosmic microwave background (CMB) during reionization. We also investigate a `cold' IGM scenario that assumes perfect Ly$\alpha$ coupling of the $21$ cm spin temperature to the temperature of the intergalactic medium (IGM), but that the IGM is not heated by early stars or stellar remants. Under this assumption, we reject tanh-based reionization models of duration $\Delta z\lesssim 2$ over most of the observed redshift range. Finally, we explore and reject a broad range of Gaussian models for the $21$ cm absorption feature expected in the First Light era. As an example, we reject $100$ mK Gaussians with duration (full width at half maximum) $\Delta z\le 4$ over the range $14.2\ge z\ge 6.5$ at $\ge 2\sigma$ significance.

References in corpus (18)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• Model-independent evidence in favor of an end to reionization by z~6
• The Global 21 Centimeter Background from High Redshifts
• 21 cm fluctuations from inhomogeneous X-ray heating before reionization
• A measurement of secondary cosmic microwave background anisotropies from the 2500-square-degree SPT-SZ survey
• Rapid Decline of Lyman-alpha Emission Toward the Reionization Era
• The low-frequency environment of the Murchison Widefield Array: radio-frequency interference analysis and mitigation
• The Global 21-cm Signal in the Context of the High-z Galaxy Luminosity Function
• All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
• Lyman-alpha emitters gone missing: evidence for late reionization?
• Spectral Index of the Diffuse Radio Background Measured From 100 to 200 MHz
• Foreground Model and Antenna Calibration Errors in the Measurement of the Sky-Averaged λ21 cm Signal at z~20
• Multi-redshift limits on the 21cm power spectrum from PAPER
• Improved Measurement of the Spectral Index of the Diffuse Radio Background Between 90 and 190 MHz
• A Space-Based Observational Strategy for Characterizing the First Stars and Galaxies Using the Redshifted 21-cm Global Spectrum
• Radiometric Measurements of Electron Temperature and Opacity of Ionospheric Perturbations
• Inversions for Deep Solar Meridional Flow Using Spherical Born Kernels

Cited by in corpus (9)

• Signature of Excess Radio Background in the 21-cm Global Signal and Power Spectrum
• Results from EDGES High-Band: III. New Constraints on Parameters of the Early Universe
• Spectral Index of the Diffuse Radio Background Between 50 and 100 MHz
• Direct millicharged dark matter cannot explain EDGES
• Formulating and critically examining the assumptions of global 21-cm signal analyses: How to avoid the false troughs that can appear in single spectrum fits
• Small-scale structure and the Lyman-$\alpha$ forest baryon acoustic oscillation feature
• Impact of inhomogeneous reionization on the Lyman-α forest
• Statistical Detection of IGM Structures during Cosmic Reionization using Absorption of the Redshifted 21 cm line by HI against Compact Background Radio Sources
• Beyond optical depth: Future determination of ionization history from the CMB