Ly$α$ forest power spectrum as an emerging window into the epoch of reionization and cosmic dawn

Paulo Montero-Camacho, Yi Mao

Published 2020-03-23Version 1

Conventional wisdom was that thermal relics from the epoch of reionization (EOR) would vanish swiftly and hence the usual intergalactic medium (IGM) temperature-density relation would be recovered rapidly. Thus the Ly$\alpha$ forest is one of the primary cosmological probes at the post-reionization epoch. Recently, however, it was shown that the imprint of cosmic reionization can survive to lower redshifts ($z \sim 2$) than previously thought. Given the high sensitivities of upcoming Ly$\alpha$ forest surveys, this effect will be a novel broadband systematic that must be tackled for cosmological application. From the astrophysical point of view, however, the imprint of inhomogeneous reionization can shed light on the EOR and cosmic dawn. We utilize a hybrid method --- which includes two different simulation codes capable of handling the huge dynamical range --- to show the impact of patchy reionization on the Ly$\alpha$ forest and its dependence on different astrophysical scenarios. We found small, but statistically significant, deviations in the 1D Ly$\alpha$ power spectrum that range from a tenth of per cent at $z = 2$ to a few per cent at $z = 4$. The deviations in the 3D Ly$\alpha$ power spectrum are considerably large and range from a few per cent at $z = 2$ up to tens of per cent at $z = 4$. By exploiting different $k$-dependence of power spectrum among various astrophysical scenarios, the effect of patchy reionization on the Ly$\alpha$ forest power spectrum can open a new window into the cosmic reionization and possibly even the cosmic dawn.