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CANDELS: The Contribution of the Observed Galaxy Population to Cosmic Reionization
Cosmology and Nongalactic Astrophysics · Submitted 4 Jun 2012
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We find that the observable population of galaxies can sustain a fully reionized IGM at z=6, if the average ionizing photon escape fraction (f_esc) is ~30%.
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The abstract, sentence by sentence
We present measurements of the specific ultraviolet luminosity density from a sample of 483 galaxies at 6<z<8. These galaxies were selected from new deep near-infrared HST imaging from the CANDELS, HUDF09 and ERS programs. In contrast to the majority of previous analyses, which assume that the distribution of galaxy ultraviolet (UV) luminosities follows a Schechter distribution, and that the distribution continues to luminosities far below our observable limit, we investigate the contribution to reionization from galaxies which we can observe, free from these assumptions. We find that the observable population of galaxies can sustain a fully reionized IGM at z=6, if the average ionizing photon escape fraction (f_esc) is ~30%. A number of previous studies have measured UV luminosity densities at these redshifts that vary by 5X, with many concluding that galaxies could not complete reionization by z=6 unless a large population of galaxies fainter than the detection limit were invoked, or extremely high values of f_esc were present. The observed UV luminosity density from our observed galaxy samples at z=7-8 is not sufficient to maintain a fully reionized IGM unless f_esc>50%. Combining our observations with constraints on the emission rate of ionizing photons from Ly-alpha forest observations at z=6, we can constrain f_esc<34% (2-sigma) if the observed galaxies are the only contributors to reionization, or <13% (2-sigma) if the luminosity function extends to M_UV = -13. These escape fractions are sufficient to complete reionization by z=6. These constraints imply that the volume ionized fraction of the IGM becomes less than unity at z>7, consistent with a number of complementary reionization probes. If faint galaxies dominate reionization, future JWST observations will probe deep enough to see them, providing an indirect constraint on the ionizing photon escape fraction [abridged].
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present measurements of the specific ultraviolet luminosity density from a sample of 483 galaxies at 6<z<8. | contribution 0.89 | 0.97 | 0.04 | asserted 1.00 |
| s1 | These galaxies were selected from new deep near-infrared HST imaging from the CANDELS, HUDF09 and ERS programs. | method 0.99 | 0.44 | 0.02 | asserted 1.00 |
| s2 | In contrast to the majority of previous analyses, which assume that the distribution of galaxy ultraviolet (UV) luminosities follows a Schechter distribution, and that the distribution continues to luminosities far below our observable limit, we investigate the contribution to reionization from galaxies which we can observe, free from these assumptions. | contribution 0.77 | 0.69 | 0.06 | asserted 0.89 |
| s3 | We find that the observable population of galaxies can sustain a fully reionized IGM at z=6, if the average ionizing photon escape fraction (f_esc) is ~30%. | result 0.99 | 0.97 | 0.58 | asserted 0.91 |
| s4 | A number of previous studies have measured UV luminosity densities at these redshifts that vary by 5X, with many concluding that galaxies could not complete reionization by z=6 unless a large population of galaxies fainter than the detection limit were invoked, or extremely high values of f_esc were present. | background 0.95 | 0.04 | 0.04 | asserted 0.88 |
| s5 | The observed UV luminosity density from our observed galaxy samples at z=7-8 is not sufficient to maintain a fully reionized IGM unless f_esc>50%. | result 0.99 | 0.94 | 0.14 | asserted 0.99 |
| s6 | Combining our observations with constraints on the emission rate of ionizing photons from Ly-alpha forest observations at z=6, we can constrain f_esc<34% (2-sigma) if the observed galaxies are the only contributors to reionization, or <13% (2-sigma) if the luminosity function extends to M_UV = -13. | result 0.98 | 0.90 | 0.17 | asserted 0.75 |
| s7 | These escape fractions are sufficient to complete reionization by z=6. | interpretation 0.80 | 0.82 | 0.29 | asserted 0.99 |
| s8 | These constraints imply that the volume ionized fraction of the IGM becomes less than unity at z>7, consistent with a number of complementary reionization probes. | interpretation 0.97 | 0.77 | 0.15 | hedged possibility 0.80 |
| s9 | If faint galaxies dominate reionization, future JWST observations will probe deep enough to see them, providing an indirect constraint on the ionizing photon escape fraction [abridged]. | future work 0.83 | 0.16 | 0.06 | hedged possibility 0.86 |
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The paper
Original abstract
We present measurements of the specific ultraviolet luminosity density from a sample of 483 galaxies at 6<z<8. These galaxies were selected from new deep near-infrared HST imaging from the CANDELS, HUDF09 and ERS programs. In contrast to the majority of previous analyses, which assume that the distribution of galaxy ultraviolet (UV) luminosities follows a Schechter distribution, and that the distribution continues to luminosities far below our observable limit, we investigate the contribution to reionization from galaxies which we can observe, free from these assumptions. We find that the observable population of galaxies can sustain a fully reionized IGM at z=6, if the average ionizing photon escape fraction (f_esc) is ~30%. A number of previous studies have measured UV luminosity densities at these redshifts that vary by 5X, with many concluding that galaxies could not complete reionization by z=6 unless a large population of galaxies fainter than the detection limit were invoked, or extremely high values of f_esc were present. The observed UV luminosity density from our observed galaxy samples at z=7-8 is not sufficient to maintain a fully reionized IGM unless f_esc>50%. Combining our observations with constraints on the emission rate of ionizing photons from Ly-alpha forest observations at z=6, we can constrain f_esc<34% (2-sigma) if the observed galaxies are the only contributors to reionization, or <13% (2-sigma) if the luminosity function extends to M_UV = -13. These escape fractions are sufficient to complete reionization by z=6. These constraints imply that the volume ionized fraction of the IGM becomes less than unity at z>7, consistent with a number of complementary reionization probes. If faint galaxies dominate reionization, future JWST observations will probe deep enough to see them, providing an indirect constraint on the ionizing photon escape fraction [abridged].
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References
How the literature uses it
8 arXiv papers cite this in 11 sentences
Papers citing it · 9 sentences without a confident label
Cites it as support 1 paper
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However, at the same time we found that the low-mass, star-forming galaxies are necessary to maintain the ionization of intergalactic medium at $z≥6$ (see also [ref] ), therefore important for the reionization of the Universe.
Duty Cycle and the Increasing Star Formation History of z>=6 Galaxies · Introduction · 0.98
Cites it as background 1 paper
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Surveys of blank fields, in particular HUDF, Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey CANDELS, and the Brightest of Reionizing Galaxies Survey BoRG (e.g., [ref] ) as well as cluster fields [ref] have been undertaken.
Spitzer UltRa Faint SUrvey Program (SURFS UP) I: An Overview · Survey Design and Sample Selection · 0.98
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