Bayesian constraints on the global 21-cm signal from the Cosmic Dawn

• Published in: Monthly notices of the Royal Astronomical Society 2016-09, Vol.461 (3), p.2847-2855
• Main Authors: Bernardi, G., Zwart, J. T. L., Price, D., Greenhill, L. J., Mesinger, A., Dowell, J., Eftekhari, T., Ellingson, S. W., Kocz, J., Schinzel, F.
• Format: Article
• Language: English
• Subjects: Amplitudes; Aperture; Apertures; Bayesian analysis; Confidence intervals; Emission; Ionization; Mathematical models; Red shift; Signal to noise ratio; Signatures; Spectrum analysis; Symbols
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw1499

The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work, we present a fully Bayesian method, hibayes, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible) Gaussian model of the 21-cm emission from the Cosmic Dawn epoch (15 ≲ z ≲ 30), parametrized by an amplitude $A_{\rm H\,\small {I}}$ , a frequency peak $\nu _{\rm H\,\small {I}}$ and a width $\sigma _{\rm H\,\small {I}}$ , can be extracted even in the presence of a structured foreground frequency spectrum (parametrized as a seventh-order polynomial), provided sufficient signal-to-noise (400 h of observation with a single dipole). We apply our method to an early, 19-min-long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be $-890 \lt A_{\rm H\,\small {I}} \lt 0$ mK and $\sigma _{\rm H\,\small {I}} \gt 6.5$ MHz (corresponding to Δz > 1.9 at redshift z ≃ 20) respectively at the 95-per cent confidence level in the range 13.2 < z < 27.4 (100 > ν > 50 MHz).