Kavli Affiliate: Nickolay Y. Gnedin
| First 5 Authors: Nickolay Y. Gnedin, Hanjue Zhu, , ,
| Summary:
Recently, several observational detections of damping-wing-like features at
the edges of “dark gaps" in the spectra of distant quasars (the “Malloy-Lidz
effect") have been reported, rendering strong support for the existence of
“neutral islands" in the universe at redshifts as low as $z<5.5$. We apply the
procedure from one of these works, citet{YZhu2024}, to the outputs of fully
coupled cosmological simulations from two recent large projects, “Cosmic
Reionization On Computers" (CROC) and “Thesan". Synthetic spectra in both
simulations have statistics of dark gaps similar to observations, but do not
exhibit the damping wing features. Moreover, a toy model with neutral islands
added “by hand" only reproduces the observational results when the fraction of
neutral islands among all dark gaps exceeds 90%. I.e., simulations and
observations appear to produce two distinct “populations" of dark gaps. In
addition, the neutral islands observed at $z=5.9$ should be short-lived and
hence cannot extend to $z<5.5$. In summary, the observational detections of
damping wing features present serious challenges not only to state-of-the-art
simulations but also to our general understanding of how reionization should
proceed.
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