Misc,
Cosmic Reionization May Still Have Started Early and Ended Late: Confronting Early Onset with CMB Anisotropy and 21 cm Global Signals
(2020)cite arxiv:2011.03582Comment: submitted to ApJ; comments welcome.
Abstract
The global history of reionization was shaped by the relative amounts of
starlight released by three halo mass groups: atomic-cooling halos (ACHs) with
virial temperatures Tvir > 10^4 K, either (1) massive enough to form stars even
after reionization (HMACHs, >~ 10^9 Msun) or (2) less-massive (LMACHs), subject
to star formation suppression when overtaken by reionization, and (3)
H2-cooling minihalos (MHs) with Tvir < 10^4 K, whose star formation is
predominantly suppressed by the H2-dissociating Lyman-Werner (LW) background.
Our previous work showed that including MHs caused two-stage reionization -
early rise to x ~ 0.1, driven by MHs, followed by a rapid rise, late, to x ~ 1,
driven by ACHs - with a signature in CMB polarization anisotropy predicted to
be detectable by the Planck satellite. Motivated by this prediction, we model
global reionization semi-analytically for comparison with Planck CMB data and
the EDGES global 21cm absorption feature, for models with: (1) ACHs, no
feedback; (2) ACHs, self-regulated; and (3) ACHs and MHs, self-regulated. Model
(3) agrees well with Planck E-mode polarization data, even with a substantial
tail of high-redshift ionization, beyond the limit proposed by the Planck
Collaboration (2018). No model reproduces the EDGES feature. For model (3),
|dTb| <~ 60 mK across the EDGES trough, an order of magnitude too shallow, and
absorption starts at higher z but is spectrally featureless. Early onset
reionization by Population III stars in MHs is compatible with current
constraints, but only if the EDGES interpretation is discounted or else other
processes we did not include account for it.
