2018MNRAS.479.4320G

We investigate the impact of quasars on the ionization of the surrounding intergalactic medium (IGM) with the radiative transfer code CRASH4, now accounting for X-rays and secondary electrons. After comparing with analytic solutions, we post-process a cosmic volume (≃1.5 x 10⁴ Mpc³ h^–3) containing a ULAS J1120+0641-like quasar (QSO) hosted by a 5 x 10¹¹ M_☉ h^–1 dark matter (DM) halo. We find that (i) the average H II region (R ∼ 3.2 pMpc in a lifetime t_f = 10⁷ yr) is mainly set by UV flux, in agreement with semi-analytic scaling relations; (ii) a largely neutral (x_H II_ < 0.001), warm (T ∼ 10³ K) tail extends up to few Mpc beyond the ionization front, as a result of the X-ray flux; and (iii) LyC-opaque inhomogeneities induce a line of sight (LOS) scatter in R as high as few physical Mpc, consistent with the DLA scenario proposed to explain the anomalous size of the ULAS J1120+0641 ionized region. On the other hand, with an ionization rate {dot}N_γ,0_ ∼10⁵⁷ s^–1, the assumed DLA clustering and gas opacity, only one LOS shows an H II region compatible with the observed one. We deduce that either the ionization rate of the QSO is at least one order of magnitude lower or the ULAS J1120+0641 bright phase is shorter than 10⁷ yr.