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On the origin of low escape fractions of ionizing radiation from massive star-forming galaxies at high redshift
Astrophysics of Galaxies · Submitted 15 Jan 2020
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass.
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The abstract, sentence by sentence
The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at $z\sim3$-$4$ is not well understood. We perform idealised disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman Continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor ($Z=0.002$) galaxy embedded in a halo of mass $M_h\simeq10^{11}\,M_\odot$ is $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 10\,\%$. Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). When the metallicity of the gas is increased to $Z=0.02$, the escape fraction is significantly reduced to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq1\%$ because young stars are enshrouded by their birth clouds for a longer time. In contrast, increasing the gas mass by a factor of 5 leads to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 5\, \%$ because LyC photons are only moderately absorbed by the thicker disc. Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass. Finally, negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at $z\sim3$-$4$ is not well understood. | gap 0.89 | 0.04 | 0.02 | asserted 0.98 |
| s1 | We perform idealised disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman Continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. | method 0.84 | 0.95 | 0.03 | asserted 0.87 |
| s2 | We find that the luminosity-weighted escape fraction from a metal-poor ($Z=0.002$) galaxy embedded in a halo of mass $M_h\simeq10^{11}\,M_\odot$ is $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 10\,\%$. | result 1.00 | 0.97 | 0.10 | asserted 1.00 |
| s3 | Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). | result 1.00 | 0.93 | 0.04 | asserted 1.00 |
| s4 | When the metallicity of the gas is increased to $Z=0.02$, the escape fraction is significantly reduced to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq1\%$ because young stars are enshrouded by their birth clouds for a longer time. | result 0.99 | 0.95 | 0.12 | asserted 1.00 |
| s5 | In contrast, increasing the gas mass by a factor of 5 leads to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 5\, \%$ because LyC photons are only moderately absorbed by the thicker disc. | result 1.00 | 0.96 | 0.05 | asserted 1.00 |
| s6 | Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass. | interpretation 1.00 | 0.78 | 0.85 | hedged possibility 1.00 |
| s7 | Finally, negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates. | result 1.00 | 0.94 | 0.04 | asserted 1.00 |
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The paper
Original abstract
The physical origin of low escape fractions of ionizing radiation derived from massive star-forming galaxies at $z\sim3$-$4$ is not well understood. We perform idealised disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman Continuum (LyC) photons using radiation-hydrodynamic simulations with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor ($Z=0.002$) galaxy embedded in a halo of mass $M_h\simeq10^{11}\,M_\odot$ is $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 10\,\%$. Roughly half of the LyC photons are absorbed within scales of 100 pc, and the other half is absorbed in the ISM ($\lesssim 2\, {\rm kpc}$). When the metallicity of the gas is increased to $Z=0.02$, the escape fraction is significantly reduced to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq1\%$ because young stars are enshrouded by their birth clouds for a longer time. In contrast, increasing the gas mass by a factor of 5 leads to $\left<f_{\rm esc}^{\rm 3D}\right>\simeq 5\, \%$ because LyC photons are only moderately absorbed by the thicker disc. Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in massive star-forming galaxies, supporting the scenario in which the escape fraction is decreasing with increasing halo mass. Finally, negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates.
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How the literature uses it
6 arXiv papers cite this in 9 sentences
Papers citing it · 4 sentences without a confident label
Compares with it 3 papers
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By comparison, stellar sources exhibit $⟨⟩≲10%$, consistent with the values found by other high-resolution reionization simulations [ref] .
The Obelisk simulation: galaxies contribute more than AGN to HI reionization of protoclusters · Relative contribution of galaxies and black holes · 0.91
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On average, the three runs present a very similar behaviour, with a fairly low average escape fraction of $∼5-7%$, consistent with the recent results of [ref] on a sample of LBGs at $z∼3$ and with the detailed simulation of [ref] of an isolated galaxy of similar mass.
Modelling a bright z = 6 galaxy at the faint end of the AGN luminosity function · Contribution from stellar populations · 0.86
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For dark matter haloes of $10^11$, the simulations of [ref] yield an escape fraction of 7%, also in rather good agreement with our results.
Galactic ionising photon budget during the Epoch of Reionisation in the Cosmic Dawn II simulation · Comparison with the literature · 0.99
Cites it as support 1 paper
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Such a dust-related decrease in galaxy escape fraction may indeed happen, as shown in some simulations [ref] .
Lyman-alpha opacities at z=4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization · Introduction · 0.97
Cites it as background 1 paper
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Recent studies do account for fully-coupled radiation-hydrodynamics, with a focus on spatial resolution, considering a single galaxy or a fraction thereof [ref] .
Galactic ionising photon budget during the Epoch of Reionisation in the Cosmic Dawn II simulation · Introduction · 0.88
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