Escape of Ionizing Radiation from High-Redshift Galaxies

By Nickolay Y. Gnedin, Andrey V. Kravtsov, Hsiao-Wen Chen. 2007

224 citations recorded by the source corpus.

We model the escape of ionizing radiation from high-redshift galaxies using high-resolution adaptive mesh refinement N-body + hydrodynamics simulations. Our simulations include the time-dependent and spatially resolved transfer of ionizing radiation in three dimensions, including the effects of dust absorption. For galaxies of total mass M≳ 1011 M☉ and star formation rates SFR ≈ 1–5 M☉ yr−1, we find angular averaged escape fractions of 1%-3% over the entire redshift interval studied (3 < z < 9). In addition, we find that the escape fraction varies by more than an order of magnitude along different lines of sight within individual galaxies, from the largest values near galactic poles to the smallest along the galactic disk. The escape fraction declines steeply at lower masses and SFR. We show that the low values of escape fractions are due to a small fraction of young stars located just outside the edge of the H I disk. This fraction, and hence the escape fraction, is progressively smaller in disks of smaller galaxies because their H I disks are thicker and more extended relative to the distribution of young stars compared to massive galaxies. We compare our predicted escape fraction of ionizing photons with previous results and find a general agreement with both other simulation results and available direct detection measurements at z ∼ 3. We also compare our simulations with a novel method to estimate the escape fraction in galaxies from the observed distribution of neutral hydrogen column densities along the lines of sight to long-duration γ-ray bursts (GRBs). Using this method we find escape fractions of the GRB host galaxies of 2%-3%, consistent with our theoretical predictions. Our results thus suggest that high-redshift galaxies are inefficient in releasing ionizing radiation produced by young stars into the intergalactic medium.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ddf177a08fa622d728f66ad30a52ed1cd5e81b37

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Citations in the corpus

CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY (2011, unknown): “The resolved LyC distributions will test different mechanisms for high fesc including SN winds (Clarke & Oey 2002; Fujita et al. 2002), and galaxy interactions (Gnedin et al. 2008).”
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse (2007, methodology): “The promising approach of Gnedin & Abel (2001) has recently been implemented and coupled with the AMR hydrodynamic code ART (Gnedin et al. 2008).”
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions (2019, background): “In parallel, early hydrodynamical simulations produced a mixture of results: with fesc correlating with halo mass (e.g., Gnedin et al. 2008; Wise & Cen 2009), anti-correlating with halo mass (e.g., Yajima et al. 2011; Paardekooper et al. 2015; Kimm et al. 2017), and typical time-averaged values far…”
CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY—THE HUBBLE SPACE TELESCOPE OBSERVATIONS, IMAGING DATA PRODUCTS, AND MOSAICS (2011, background): “The resolved LyC distributions provide tests of different mechanisms for high fesc including SNe winds (Clarke & Oey 2002, Fujita et al. 2002), minor galaxy interactions (Gnedin et al. 2008), and emission from globular cluster formation (Ricotti 2002).”
The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “Attempts to constrain the escape fraction with numerical simulations find ranges between fesc < 10% (Razoumov & Sommer-Larsen 2006, 2007; Gnedin et al. 2008; Paardekooper et al. 2011; Kim et al. 2013) and fesc > 80% (Wise & Cen 2009; Razoumov & Sommer-Larsen 2010), with likely a strong mass and…”
CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION (2012, background): “Various other models find that the escape fraction varies (either higher or lower) with halo mass due to a variety of effects (e.g., Gnedin et al. 2008; Wise & Cen 2009), including holes in the ISM from supernovae (e.g., Yajima et al. 2009).”
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization (2016, background): “An early attempt by Gnedin et al. (2008) suggested that the escape fraction roughly increases with halo mass in the range 1010–1012 M , because stellar disks c© 0000 The Authors ar X iv :1 60 8.”
Fluctuations in the high-redshift Lyman–Werner background: close halo pairs as the origin of supermassive black holes (2008, background): “Chen et al. (2007) show that fesc may obtain a wide range of values, and that 〈fesc〉 = 0.02, in good agreement with theoretical calculations of the escape fraction of ionizing photons from galaxies in adaptive mesh refinement hydrodynamical simulations6 by Gnedin et al. (2008).”
GeV gamma-ray attenuation and the high-redshift UV background (2009, methodology): “As noted in Gnedin et al. (2008), taking the total absorption to be a product of the dust and H I factors may not be physically realistic, as the two components are may not be distributed in the same way within the galaxy, however it is sufficient for the purpose of calculating emissivities, as we…”
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal (2015, result): “…choice of Nγ ≈ 4000 is expected from Population II stars (e.g. Barkana & Loeb 2005), while f? and fesc are extremely uncertain in high-z galaxies (e.g. Gnedin et al. 2008; Wise & Cen 2009; Ferrara & Loeb 2013), though our choices are consistent with observations of galaxy luminosity functions…”
THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. I. JAMES WEBB SPACE TELESCOPE DETECTION LIMITS AND COLOR CRITERIA FOR POPULATION III GALAXIES (2011, background): “Simulations predict that the amount of Lyman continuum escape may be a function of dark halo mass (Gnedin et al. 2008; Razoumov & Sommer-Larsen 2010; Yajima et al. 2011), but the likely escape fraction and its exact mass dependence remains controversial.”
The First Billion Years project: the impact of stellar radiation on the co-evolution of Populations II and III (2012, background): “…for the escape fraction fesc of ionizing photons expected for Pop III star-forming haloes (e.g. Alvarez et al. 2006; Johnson et al. 2009) as compared to Pop II galaxies (e.g. Gnedin et al. 2008), implies that the relative contribution of Pop III stars to reionization may have been relatively large.”
Signatures of X-rays in the early Universe (2012, background): “On the other hand, the parameters fesc and f∗ are extremely uncertain in high-redshift galaxies (e.g. Gnedin et al. 2008; Wise & Cen 2009; Ferrara & Loeb 2012), though their product might be more robust (Wise & Cen 2009; Paardekooper et al. 2011).”
Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, result): “This is in line with the more recent findings of Gnedin et al. (2008), Wise & Cen (2009), Kim et al. (2013) and Paardekooper et al. (2015) who showed that the ionizing radiation escapes anisotropically, favouring low column density regions resulting from such outflows.”