Probing the Epoch of Reionization with the Lyman Alpha Forest at Z

The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z ∼ 4− 5. The Lyman-α forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the expected full SDSS III quasar sample (∼ 10, 000 quasars) we show that two cosmological reionization scenarios, one completing reionization at z = 6 and the other at z = 9, can be distinguished at ∼ 7σ level by utilizing Lyα forest absorption spectra at z = 4.5 ± 0.5, in the absence of other physical processes that may also affect the Lyα flux power spectrum. The redshift range z = 4 − 5 may provide the best window, because there is still enough transmitted flux and quasars to measure precise statistics of the flux fluctuations, and the IGM still retains a significant amount of memory of reionization.