Inhomogeneous recombinations during cosmic reionization

By E. Sobacchi, A. Mesinger. 2014

133 citations recorded by the source corpus.

By depleting the ionizing photon budget available to expand cosmic HII regions, recombining systems (or Lyman limit systems) can have a large impact during (and following) cosmic reionization. Unfortunately, directly resolving such structures in large-scale reionization simulations is computationally impractical. Instead, here we implement a sub-grid prescription for tracking inhomogeneous recombinations in the intergalactic medium. Building on previous work parameterizing photo-heating feedback on star-formation, we present large-scale, semi-numeric reionization simulations which self-consistently track the local (sub-grid) evolution of both sources and sinks of ionizing photons. Our simple, single-parameter model naturally results in both an extended reionization and a modest, slowly-evolving emissivity, consistent with observations. Recombinations are instrumental in slowing the growth of large HII regions, and damping the rapid rise of the ionizing background in the late stages of (and following) reionization. As a result, typical HII regions are smaller by factors of $\sim 2-3$ throughout reionization. The large-scale ($k\lesssim 0.2\text{ Mpc$^{-1}$}$) ionization power spectrum is suppressed by factors of $\gtrsim 2-3$ in the second half of reionization. Therefore properly modeling recombinations is important in interpreting virtually all reionization observables, including upcoming interferometry with the redshifted 21 cm line. Consistent with previous works, we find the clumping factor of ionized gas to be $C_{\rm HII}\sim 4$ at the end of reionization.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/eacd2083b637620a021076fcbe50ea8fb019f208

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In Astronomy and Astrophysics

1. Richard S. Ellis
2. L. Hernquist
3. P. Hopkins
4. P. Oesch
5. J. Dunlop
6. D. Stark
7. C. Conroy
8. Brant Robertson

Citations in the corpus

• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “…The observed LAE clustering function at z∼6.6 (Ouchi et al. 2010), when interpreted in the context of the clustering in detailed reionization simulations, suggests <x 0.5H I¯ (Sobacchi & Mesinger 2014), which we implement as a half-Gaussian peaked at zero with σ=0.5 (Greig & Mesinger 2017).”
• The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, methodology): “An accurate model of reionization must include realistic large-scale IGM structure (Trac et al. 2008; Iliev et al. 2014; Sobacchi & Mesinger 2014).”
• NEW OBSERVATIONS OF z ∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION (2014, background): “However such a rapid evolution of the photo-ionizing background could be very difficult to achieve without requiring either a late reionization, or an emissivity at z 6 which is too high to be consistent with observations of the Lyα forest (e.g. Sobacchi & Mesinger 2014).”
• Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six (2014, background): “…the local mean free path will still evolve rapidly and exhibit a degree of spatial variance as residual patches of neutral hydrogen and/or Lyman limit systems at the edges of H ii regions are ionized (e.g., Furlanetto & Oh 2005; Choudhury et al. 2009; Alvarez & Abel 2012; Sobacchi & Mesinger 2014).”
• Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, methodology): “…is“photon-starved”as suggested by emissivity estimates from the Lyman alpha forest, recombinations would “stall” the growth of large H ii regions (e.g. Miralda-Escudé et al. 2000; Ciardi et al. 2006; McQuinn et al. 2007; Finlator et al. 2012; Kaurov & Gnedin 2014; Sobacchi & Mesinger 2014).”
• Modeling the Radio Background from the First Black Holes at Cosmic Dawn: Implications for the 21 cm Absorption Amplitude (2018, background): “Furthermore, it is possible that fine-scale, optically thick substructures, such as Damped Lyα systems, can delay ionization further by Δz≈2 (Sobacchi & Mesinger 2014).”
• Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization (2014, background): “Such a striking evolution in the ionization state of the IGM seems unphysical over such a brief period of cosmic history (e.g., Sobacchi & Mesinger 2014; Robertson et al. 2013; Mesinger et al. 2014).”
• Can the intergalactic medium cause a rapid drop in Lyα emission at z > 6? (2014, methodology): “For our ionization fields, we use the results from Sobacchi & Mesinger (2014), which include inhomogeneous, sub-grid c© 0000 RAS, MNRAS 000, 000–000 modeling of (i) UV feedback on galaxies; and (ii) recombinations.”
• The Evolution of the Intergalactic Medium (2015, background): “…the unresolved dense structures that act as sinks of ionizing photons, studies find that the sinks act to cap the maximum ionized bubble size at roughly the photon mean free path to intersect a sink (Furlanetto & Oh 2005; McQuinn et al. 2007b; Alvarez & Abel 2012; Sobacchi & Mesinger 2014).”
• 21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal (2015, methodology): “Nevertheless, an effective, uniform maximum horizon for ionizing photons of ∼ 10 Mpc can reproduce the 21 cm power spectra of the Sobacchi & Mesinger (2014) simulations to within tens of percent on relevant scales, at the epochs studied in that work 0.25 . x̄H I .”