Hydrodynamic Response of the Intergalactic Medium to Reionization II: Physical Characteristics and Dynamics of Ionizing Photon Sinks

Abstract

Becker et al. 2021 measured the mean free path of Lyman limit photons in the IGM at $z=6$. The short value suggests that absorptions may have played a prominent role in reionization. Here we study physical properties of ionizing photon sinks in the wake of ionization fronts (I-fronts) using radiative hydrodynamic simulations. We quantify the contributions of gaseous structures to the Lyman limit opacity by tracking the column density distributions in our simulations. Within $\Delta t=10$ Myr of I-front passage, we find that self-shielding systems ($N_{\mathrm{HI}}>10^{17.2}$ cm${}^{-2}$) are comprised of two distinct populations: (1) over-density $\Delta \sim 50$ structures in photo-ionization equilibrium with the ionizing background; (2) $\Delta \gtrsim 100$ density peaks with fully neutral cores. The self-shielding systems contribute more than half of the opacity at these times, but the IGM evolves considerably in $\Delta t\sim 100$ Myr as structures are flattened by pressure smoothing and photoevaporation. By $\Delta t=300$ Myr, they contribute $\lesssim 10\%$ to the opacity in an average 1 Mpc${}^3$ patch of the Universe. The percentage can be a factor of a few larger in over-dense patches, where more self-shielding systems survive. We quantify the characteristic masses and sizes of self-shielding structures. Shortly after I-front passage, we find $M=10^4-10^8$ M${}_{\odot }$ and effective diameters $d_{\mathrm{eff}}=1-20$ ckpc$/h$. These scales increase as the gas relaxes. The picture herein presented may be different in dark matter models with suppressed small-scale power.

19 pages, 11 figures, 1 table submitted to ApJ

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Cited by in corpus (11)

• The Sherwood-Relics simulations: overview and impact of patchy reionization and pressure smoothing on the intergalactic medium
• The Morphology of Reionization in a Dynamically Clumpy Universe
• Constraints on the $z\sim 6-13$ intergalactic medium from JWST spectroscopy of Lyman-alpha damping wings in galaxies
• The impact and response of minihalos and the inter-halo medium on cosmic reionization
• Mapping reionization bubbles in the JWST era I: empirical edge detection with Lyman alpha emission from galaxies
• Small-scale clumping of dark matter and the mean free path of ionizing photons at $z=6$
• The Lyman-limit photon mean free path at the end of late reionisation in the Sherwood-Relics simulations
• A Global Census of Metals in the Universe
• Reionizing islands with inhomogeneous recombinations
• Kiloparsec-scale turbulence driven by reionization may grow intergalactic magnetic fields
• An emulator for the ionizing photon mean free path in ultra-high resolution simulations: the implications of mean free path measurements for the reionization history