INTERPRETING THE GLOBAL 21-cm SIGNAL FROM HIGH REDSHIFTS. II. PARAMETER ESTIMATION FOR MODELS OF GALAXY FORMATION

Abstract

Following our previous work, which related generic features in the sky-averaged (global) 21-cm signal to properties of the intergalactic medium, we now investigate the prospects for constraining a simple galaxy formation model with current and near-future experiments. Markov-Chain Monte Carlo fits to our synthetic dataset, which includes a realistic galactic foreground, a plausible model for the signal, and noise consistent with 100 hours of integration by an ideal instrument, suggest that a simple four-parameter model that links the production rate of Lyman-α, Lyman-continuum, and X-ray photons to the growth rate of dark matter halos can be well-constrained (to ∼ 0.1 dex in each dimension) so long as all three spectral features expected to occur between 40 ν/MHz 120 are detected. Several important conclusions follow naturally from this basic numerical result, namely that measurements of the global 21-cm signal can in principle (i) identify the characteristic halo mass threshold for star formation at all redshifts z 15, (ii) extend z 4 upper limits on the normalization of the X-ray luminosity star-formation rate (L X -SFR) relation out to z ∼ 20, and (iii) provide joint constraints on stellar spectra and the escape fraction of ionizing radiation at z ∼ 12. Though our approach is general, the importance of a broad-band measurement renders our findings most relevant to the proposed Dark Ages Radio Explorer, which will have a clean view of the global 21-cm signal from ∼ 40 − 120 MHz from its vantage point above the radio-quiet, ionosphere-free lunar far-side.

CALIBRATION OF THE EDGES HIGH-BAND RECEIVER TO OBSERVE THE GLOBAL 21 cm SIGNATURE FROM THE EPOCH OF REIONIZATION

“…The observable quantity corresponds to a differential brightness temperature that depends on the fraction of neutral hydrogen and the spin temperature of the gas. This temperature encodes the effects on the IGM of UV and X-ray radiation from the first generations of stars and stellar remnants (Mirocha et al 2013(Mirocha et al , 2015Fialkov et al 2014aFialkov et al , 2014bFialkov & Loeb 2016). For  z 6, the largescale evolution of the IGM is captured as wideband features in the frequency spectrum of the brightness temperature below ∼200 MHz, with expected absolute amplitudes lower than ∼200 mK (Mesinger et al 2013;Cohen et al 2016;Fialkov et al 2016;Mirocha et al 2016).…”

“…For reference, Figure 1 shows three phenomenological models for this signal, parameterized in terms of the redshift (z r ) and duration (Dz) of reionization (Bowman & Rogers 2010;Pritchard & Loeb 2010;Morandi & Barkana 2012;Liu et al 2013;Mirocha et al 2015;Harker et al 2016).…”

Extracting the 21cm Global Signal using Artificial Neural Networks

“…This parameterization is very flexible and can describe a wide range of 21cm signals, but the turning point positions require further interpretation in order to relate them to the physics of the first sources (Mirocha et al 2013). The tanh parameterization (Harker 2015;Mirocha et al 2015), uses a set of tanh functions to model the Global signal. In Bernardi et al (2015,2016), the absorption feature is modelled as a Gaussian.…”

A Space-based Observational Strategy for Characterizing the First Stars and Galaxies Using the Redshifted 21 cm Global Spectrum

“…Unlike previous papers (e.g., Mirocha et al 2015;Harker et al 2016), which assumed perfect knowledge of the instrument, this new process accounts for and propagates the uncertainty in the instrumental parameters to the signal extraction pipeline. Our instrument sensitivity metric is defined as the rms uncertainty of the extracted 21 cm spectrum, averaged over the observation band.…”