Speaker
Dr
Keri Dixon
(University of Sussex)
Description
Recent HeII Lyα forest observations from 2.0 < z < 3.4 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating HeII-ionizing background, possibly due to the end of helium reionization. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. Spanning a large parameter space, we find order-of-magnitude fluctuations in the HeII ionization rate in the post-reionization regime that increase during reionization. As in previous studies, we show that the rarity of quasars and the inhomogeneous intergalactic medium induce order unity fluctuations in the mean HeII Lyα optical depth even after reionization, even when averaged over large segments (~10 − 100 Mpc in length). We then compare to the latest observations, demonstrating that ongoing reionization readily explains the large fluctuations in the Lyα forest transmission, and examine the possibility of using the quasar proximity effect to probe the HeII-ionizing background.
