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Fully Coupled Simulation of Cosmic Reionization. III. Stochastic Early Reionization by the Smallest Galaxies
Cosmology and Nongalactic Astrophysics · Submitted 28 Apr 2017
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim With MCs, reionization starts earlier than if only halos of $10^8 M_{\odot}$ and above are included, however the redshift when reionization completes is only marginally affected as this is driven by more massive galaxies.
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The abstract, sentence by sentence
Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. Despite their low star formation rates, these Metal Cooling halos (MCs) are significant sources of ionizing radiation, especially at the onset of reionization, due to their high number density and ionizing escape fractions. Here we present a fully-coupled radiation hydrodynamic simulation of reionization that includes these MCs as well the more massive hydrogen atomic line cooling halos. Our method is novel: we perform halo finding inline with the radiation hydrodynamical simulation, and assign escaping ionizing fluxes to halos using a probability distribution function (PDF) measured from the galaxy-resolving Renaissance Simulations. The PDF captures the mass dependence of the ionizing escape fraction as well as the probability that a halo is actively forming stars. With MCs, reionization starts earlier than if only halos of $10^8 M_{\odot}$ and above are included, however the redshift when reionization completes is only marginally affected as this is driven by more massive galaxies. Because star formation is intermittent in MCs, the earliest phase of reionization exhibits a stochastic nature, with small H II regions forming and recombining. Only later, once halos of mass $\sim 10^9 M_{\odot}$ and above begin to dominate the ionizing emissivity, does reionization proceed smoothly in the usual manner deduced from previous studies. This occurs at $z\approx 10$ in our simulation.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. | background 0.88 | 0.67 | 0.13 | hedged possibility 0.60 |
| s1 | These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. | background 0.70 | 0.30 | 0.04 | asserted 1.00 |
| s2 | Despite their low star formation rates, these Metal Cooling halos (MCs) are significant sources of ionizing radiation, especially at the onset of reionization, due to their high number density and ionizing escape fractions. | background 0.52 | 0.42 | 0.12 | asserted 1.00 |
| s3 | Here we present a fully-coupled radiation hydrodynamic simulation of reionization that includes these MCs as well the more massive hydrogen atomic line cooling halos. | contribution 0.91 | 0.92 | 0.07 | asserted 1.00 |
| s4 | Our method is novel: we perform halo finding inline with the radiation hydrodynamical simulation, and assign escaping ionizing fluxes to halos using a probability distribution function (PDF) measured from the galaxy-resolving Renaissance Simulations. | method 0.94 | 0.96 | 0.04 | asserted 1.00 |
| s5 | The PDF captures the mass dependence of the ionizing escape fraction as well as the probability that a halo is actively forming stars. | method 0.99 | 0.71 | 0.04 | asserted 1.00 |
| s6 | With MCs, reionization starts earlier than if only halos of $10^8 M_{\odot}$ and above are included, however the redshift when reionization completes is only marginally affected as this is driven by more massive galaxies. | result 0.95 | 0.90 | 0.37 | asserted 0.99 |
| s7 | Because star formation is intermittent in MCs, the earliest phase of reionization exhibits a stochastic nature, with small H II regions forming and recombining. | result 0.85 | 0.85 | 0.14 | asserted 1.00 |
| s8 | Only later, once halos of mass $\sim 10^9 M_{\odot}$ and above begin to dominate the ionizing emissivity, does reionization proceed smoothly in the usual manner deduced from previous studies. | result 0.69 | 0.76 | 0.22 | asserted 1.00 |
| s9 | This occurs at $z\approx 10$ in our simulation. | result 0.99 | 0.93 | 0.07 | asserted 1.00 |
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The paper
Original abstract
Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. Despite their low star formation rates, these Metal Cooling halos (MCs) are significant sources of ionizing radiation, especially at the onset of reionization, due to their high number density and ionizing escape fractions. Here we present a fully-coupled radiation hydrodynamic simulation of reionization that includes these MCs as well the more massive hydrogen atomic line cooling halos. Our method is novel: we perform halo finding inline with the radiation hydrodynamical simulation, and assign escaping ionizing fluxes to halos using a probability distribution function (PDF) measured from the galaxy-resolving Renaissance Simulations. The PDF captures the mass dependence of the ionizing escape fraction as well as the probability that a halo is actively forming stars. With MCs, reionization starts earlier than if only halos of $10^8 M_{\odot}$ and above are included, however the redshift when reionization completes is only marginally affected as this is driven by more massive galaxies. Because star formation is intermittent in MCs, the earliest phase of reionization exhibits a stochastic nature, with small H II regions forming and recombining. Only later, once halos of mass $\sim 10^9 M_{\odot}$ and above begin to dominate the ionizing emissivity, does reionization proceed smoothly in the usual manner deduced from previous studies. This occurs at $z\approx 10$ in our simulation.
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References
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6 arXiv papers cite this in 7 sentences
Papers citing it · 6 sentences without a confident label
Cites it as background 1 paper
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There has been a surge of cosmological RHD reionization simulation projects that have captured the large-scale reionization process [ref] , with volume widths ranging from $∼10-600$ cMpc.
The SPHINX Cosmological Simulations of the First Billion Years: the Impact of Binary Stars on Reionization · Introduction · 0.98
What it cites · 6 sentences without a confident label
Compares with 1 paper
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[ref] find that LMACHs begin to dominate minihalos at $z≈17$ (see their Fig. 15), whereas we find they are subdominant at all redshifts prior to overlap (Fig. 7).
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionisation · Comparable works · 0.90
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