Enhanced detectability of pre-reionization 21 cm structure

Abstract

Before the universe was reionized, it was likely that the spin temperature of intergalactic hydrogen was decoupled from the cosmic microwave background (CMB) by UV radiation from the first stars through theWouthuysen-Field effect. If the intergalactic medium (IGM) had not yet been heated above the CMB temperature by that time, then the gas would appear in absorption relative to the CMB. Large, rare sources of X-rays could inject sufficient heat into the neutral IGM, so that δTb > 0 at comoving distances of tens to hundreds of Mpc, resulting in large 21 cm fluctuations with δT b ≃ 250 mK on arcminute to degree angular scales, an order of magnitude larger in amplitude than that caused by ionized bubbles during reionization, δTb ≃ 25 mK. This signal could therefore be easier to detect and probe higher redshifts than that due to patchy reionization. For the case in which the first objects to heat the IGM are QSOs hosting 107M⊙ black holes with an abundance exceeding ∼1 Gpc-3 at z ∼ 15, observations with either the Arecibo Observatory or the Five Hundred Meter Aperture Spherical Telescope could detect and image their fluctuations at greater than 5σ significance in about a month of dedicated survey time. Additionally, existing facilities such as MWA and LOFAR could detect the statistical fluctuations arising from a population of 105M⊙ black holes with an abundance of ∼10 4 Gpc-3 at z ≃ 10-12. © 2010. The American Astronomical Society. All rights reserved.