Linked from
The 28 pages that link to Reionization, each with the reason it gives.
QuasarRelated: The spectra of distant quasars constrain when this transition occurred.
Intergalactic mediumRelated: It marks a major change in the medium’s state and transparency.
Lookback timeRelated: Its era is probed by light from sources at very large lookback times.
Dark galaxyRelated: Reionization could heat gas and suppress star formation in low-mass halos.
Lyman-alpha emitterRelated: Emitter visibility can reveal how neutral gas changed during this epoch.