Self-shielding of hydrogen in the IGM during the epoch of reionization

Abstract

We investigate self-shielding of intergalactic hydrogen against ionizing radiation in radiative transfer simulations of cosmic reionization carefully calibrated with Lyman alpha forest data. While self-shielded regions manifest as Lyman-limit systems in the post-reionization Universe, here we focus on their evolution during reionization (redshifts z=6-10). At these redshifts, the spatial distribution of hydrogen-ionizing radiation is highly inhomogeneous, and some regions of the Universe are still neutral. After masking the neutral regions and ionizing sources in the simulation, we find that the hydrogen photoionization rate depends on the local hydrogen density in a manner very similar to that in the post-reionization Universe. The characteristic physical hydrogen density above which self-shielding becomes important at these redshifts is about ${\mathrm{n}}_{\mathrm{H}}\sim 3\times 10^{-3}\mathrm{c}{\mathrm{m}}^{-3}$, or $\sim$ 20 times the mean hydrogen density, reflecting the fact that during reionization photoionization rates are typically low enough that the filaments in the cosmic web are often self-shielded. The value of the typical self-shielding density decreases by a factor of 3 between redshifts z=3 and 10, and follows the evolution of the average photoionization rate in ionized regions in a simple fashion. We provide a simple parameterization of the photoionization rate as a function of density in self-shielded regions during the epoch of reionization.

13 pages, 10 figures, accepted for publication in MNRAS

References in corpus (15)

• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• Model-independent evidence in favor of an end to reionization by z~6
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >5: Evidence for a photon starved and extended epoch of reionization
• Studying Reionization with Ly-alpha Emitters
• Keeping the Universe ionised: Photo-heating and the clumping factor of the high-redshift intergalactic medium
• Can the intergalactic medium cause a rapid drop in Lyman alpha emission at z>6?
• Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
• A radiative transfer scheme for cosmological reionization based on a local Eddington tensor
• Through Thick and Thin - HI Absorption in Cosmological Simulations
• Lyman-alpha emitters gone missing: evidence for late reionization?
• TRAPHIC - Radiative Transfer for Smoothed Particle Hydrodynamics Simulations
• Measurement of the small-scale structure of the intergalactic medium using close quasar pairs
• Observations of the Lyman series forest towards the redshift 7.1 quasar ULAS J1120+0641
• Models of the Cosmological 21 cm Signal from the Epoch of Reionization Calibrated with Lyman-alpha and CMB Data
• 21-cm signatures of residual HI inside cosmic HII regions during reionization

Cited by in corpus (28)

• Large Lyman-alpha opacity fluctuations and low CMB tau in models of late reionization with large islands of neutral hydrogen extending to z<5.5
• Long troughs in the Lyman-$\alpha$ forest below redshift 6 due to islands of neutral hydrogen
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• Understanding the escape of LyC and Ly$\alpha$ photons from turbulent clouds
• A survey of high-$z$ galaxies: SERRA simulations
• Hydrodynamic Response of the Intergalactic Medium to Reionization
• Lyman-alpha emitters gone missing: the different evolution of the bright and faint populations
• Modelling the observed luminosity function and clustering evolution of Lyman-$\alpha$ emitters: growing evidence for late reionization
• Lyman-alpha opacities at z=4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization
• A deep learning model to emulate simulations of cosmic reionization
• Simulating the effect of photoheating feedback during reionization
• A Census of the LyC Photons that Form the UV Background During Reionization
• Hydrodynamic Response of the Intergalactic Medium to Reionization II: Physical Characteristics and Dynamics of Ionizing Photon Sinks
• Probing the thermal history during reionization using a semi-numerical photon-conserving code SCRIPT
• The mean free path of hydrogen ionizing photons during the epoch of reionization
• Constraining Reionization in Progress at z=5.7 with Lyman-$\alpha$ Emitters: Voids, Peaks, and Cosmic Variance
• The detectability of strong 21 centimetre forest absorbers from the diffuse intergalactic medium in late reionisation models
• On the accuracy of common moment-based radiative transfer methods for simulating reionization
• Revised estimates of CMB $B$-mode polarization induced by patchy reionization
• Implications of the $z>5$ Lyman-$\alpha$ forest for the 21-cm power spectrum from the epoch of reionization
• Probing delayed-end reionization histories with the 21cm-LAE cross-power spectrum
• 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
• Effective Viscosity in the Intracluster Medium During Magnetic Field Amplification via Turbulent Dynamo
• Modified Cosmology or Modified Galaxy Astrophysics is Driving the z>6 JWST Results? CMB Experiments can discover the Origin in the Near Future
• Free-floating molecular clumps and gas mixing: hydrodynamic aftermaths of the intracluster$-$interstellar medium interaction
• Radiative transfer of 21-cm line through ionised cavities in an expanding universe
• Can UVB variations reconcile simulated quasar absorption lines at high redshift?