The global 21-cm signal in the context of the high-zgalaxy luminosity function

Abstract

We build a new model for the global 21-cm signal that is calibrated to measurements of the high-z galaxy luminosity function (LF) and further tuned to match the Thomson scattering optical depth of the cosmic microwave background, τ e . Assuming that the z 8 galaxy population can be smoothly extrapolated to higher redshifts, the recent decline in best-fit values of τ e and the inefficient heating induced by X-ray binaries (the presumptive sources of the high-z X-ray background) imply that the entirety of cosmic reionization and reheating occurs at z 12. In contrast to past global 21-cm models, whose z ∼ 20 (ν ∼ 70 MHz) absorption features and strong ∼ 25 mK emission features were driven largely by the assumption of efficient early star-formation and Xray heating, our new models peak in absorption at ν ∼ 110 MHz at depths ∼ −160 mK and have negligible emission components. Current uncertainties in the faint-end of the LF, binary populations in star-forming galaxies, and UV and X-ray escape fractions introduce ∼ 20 MHz (∼ 50 mK) deviations in the trough's frequency (amplitude), while emission signals remain weak ( 10 mK) and are confined to ν 140 MHz. These predictions, which are intentionally conservative, suggest that the detection of a 21-cm absorption minimum at frequencies below ∼ 90 MHz and/or emission signals stronger than ∼ 10 mK at ν 140 MHz would provide strong evidence for "new" sources at high redshifts, such as Population III stars and their remnants.

First Results on the Epoch of Reionization from First Light with SARAS 2

“…However, Fialkov et al (2014) showed that late heating, in which reionization features strong 21-cm absorption due to a still-cold IGM, is quite plausible, opening up a wide variety of possible 21-cm signals. Extrapolations of recent observations to high redshift also support such scenarios (Madau & Fragos 2016;Mirocha et al 2017).…”

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

“…Some recent cosmological models yield large or late absorption features, or rapid reionization histories within the EDGES High-Band range (Mirocha et al 2013;Fialkov et al 2014aFialkov et al , 2014bKaurov & Gnedin 2015;Cohen et al 2016;Fialkov & Loeb 2016;Fialkov et al 2016;Mirocha et al 2016). These models should also be accessible with a similar instrument performance.…”

“…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).…”

Constraining primordial black holes with the EDGES 21-cm absorption signal

“…Because the intensity of the detected signal is proportional to I 21 cm ∝ 1 − ðT R ðzÞ=T S ðzÞÞ, where T S is the spin temperature of the atomic hydrogen and T R is the temperature of background radiation, the very first studies of the EDGES anomaly ascribed the extra absorption to a new cooling mechanism for the hydrogen gas, based on baryon-dark matter (DM) interactions [2][3][4][5][6][7] (this idea was studied before the EDGES anomaly appeared in Refs. [8][9][10]), on modified onset of star formation [11,12], or on the effects of dark energy [13,14]. DM annihilations [15][16][17] and black hole accretion [18], however, result in the injection of particles characterized by a broad energy spectrum that inevitably lead to heating the hydrogen clouds.…”