A Short Mean Free Path at z = 6 Favors Late and Rapid Reionization by Faint Galaxies

Recent measurements of the ionizing photon mean free path ($\lambda_{912}^{\rm mfp}$) at $5 < z 6$ suggest that IGM was rapidly evolving those times. We use radiative transfer simulations to explore implications for reionization, with a focus on short value $\lambda_{912}^{\rm mfp} = 3.57^{+3.09}_{-2.14}$ cMpc/$h$ $z=6$. introduce model sub-resolution sinks based hydrodynamics small-scale clumping. argue rapid evolution in mfp}$ $z=5-6$, together constraints metagalactic background, favors late reionization process which neutral fraction evolved latter half. also mfp}(z=6)$ points faint galaxies as primary drivers reionizaton. Our preferred model, mfp}(z=6) 6.5$ Mpc/$h$, has midpoint $z= 7.1$ and ends 5.1$. It requires 3 photons per H atom complete LyC production efficiency $\log(f^{\rm eff}_{\rm esc} \xi_{\rm ion}/[\mathrm{erg}^{-1} \mathrm{Hz}]) 24.8$ $z>6$. Recovering low measured central may require an increase clumpiness beyond predictions from simulations, commensurate budget.