Mapping Neutral Hydrogen During Reionization with the Ly-alpha Emission from Quasar Ionization Fronts

Understand

We present a new method to directly map the neutral-hydrogen distribution during the reionization epoch and to constrain the emission properties of the highest-redshift quasars (QSOs).

• As a tracer of HI, we propose to use the Ly-alpha radiation produced by quasar ionization fronts (I-fronts) that expand in the partially ionized intergalactic medium (IGM) before reionization is complete.
• These Ly-alpha photons are mainly generated by collisional excitations of hydrogen atoms in the boundary of the rapidly expanding HII region.
• The observable signal is produced by the part of the I-front that lies behind the QSO with respect to the observer.