The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization

By Jan-Pieter Paardekooper, S. Khochfar, Claudio Dalla Vecchia. 2015

160 citations recorded by the source corpus.

Proto-galaxies forming in low-mass dark matter haloes are thought to provide the majority of ionizing photons needed to reionize the Universe, due to their high escape fractions of ionizing photons. We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form, by computing escape fractions in more than 75000 haloes between redshifts 27 and 6 that were extracted from the First Billion Years project, high-resolution cosmological hydrodynamics simulations of galaxy formation. We find that the main constraint on the escape fraction is the gas column density in a radius of 10 pc around the stellar populations, causing a strong mass dependence of the escape fraction. The lower potential well in haloes with virial mass below 1e8 solar mass results in low column densities that can be penetrated by radiation from young stars (age < 5 Myr). In haloes with virial mass above 1e8 solar mass supernova feedback is important, but only 30% of the haloes in this mass range have an escape fraction higher than 1%. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. This makes it very hard to predict the escape fraction on the basis of halo properties and results in a highly anisotropic escape fraction. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionization and is something current models of cosmic reionization should strive to take into account.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0151dc98a6dc6992e6926a9700e99324cd60f4f6

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In Astronomy and Astrophysics

1. Volker Springel
2. R. Dav'e
3. P. Hopkins
4. L. Hernquist
5. J. Devriendt
6. S. Khochfar
7. C. Conroy
8. A. Slyz

Citations in the corpus

• Inferring the astrophysics of reionization and cosmic dawn from galaxy luminosity functions and the 21-cm signal (2018, background): “…al. 2016; Sun & Furlanetto 2016) based on observations of luminosity functions (LFs) as well as hydrodynamic simulations (e.g. Gnedin & Kaurov 2014; Paardekooper et al. 2015; Ocvirk et al. 2016; Xu et al. 2016; Kimm et al. 2017; Katz et al. 2018), suggest that both of these quantities have a more…”
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “Paardekooper et al. (2015) showed that an external ionizing background results in the photoevaporation of gas in low mass haloes, helping to increase fesc.”
• GALAXY PROPERTIES AND UV ESCAPE FRACTIONS DURING THE EPOCH OF REIONIZATION: RESULTS FROM THE RENAISSANCE SIMULATIONS (2016, background): “…clouds, there has been some convergence, showing that low-mass ( M Mlog 8vir ) halos have higher mean fesc values 25% (Wise et al. 2014; Paardekooper et al. 2015) that then decrease with halo mass to approach ∼5%–15% in more massive (logMvir/ M = 8–11) galaxies at z 6 (Kimm & Cen 2014;…”
• Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, methodology): “…other recent simulations, which find escape fractions over nearly the full possible range, often with a mass and/or redshift dependence (e.g., Razoumov & SommerLarsen 2006; Gnedin et al. 2008; Wise & Cen 2009; Paardekooper et al. 2011, 2015; Yajima et al. 2011; Kim et al. 2013; Wise et al. 2014).”
• Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, methodology): “…often predict very high escape fractions of fesc >∼ 50% in atomic cooling haloes, but these conclusions may be subject to numerical resolution (Ma et al. 2015; Paardekooper et al. 2015) and how the escape fraction is measured (i.e. whether or not it is photon number-weighted (Kimm & Cen 2014)).”
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “However, if we consider the anisotropy, stochasticity, and evolution with z of fesc that recent simulations have brought to light (e.g., Paardekooper et al. 2015; Trebitsch et al. 2017; Rosdahl et al. 2018), along with a higher CGM +IGM opacity, the limits from these studies are far less stringent…”
• A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation (2018, methodology): “Such complex relationships hold for other galaxy properties (Paardekooper et al. 2015), but no clear dependence was found (Yajima et al. 2014).”
• Large Ly α opacity fluctuations and low CMB τ in models of late reionization with large islands of neutral hydrogen extending to z < 5.5 (2018, background): “…to the evolution of the escape fraction of ionizing photons from galaxies, possibly due to changes in morphology, stellar populations, and dust con- tent of these galaxies (Rosdahl et al. 2018; Trebitsch et al. 2017; Kimm et al. 2017; Paardekooper et al. 2015; Kimm & Cen 2014; Yajima et al. 2011).”