The mean free path of ionizing photons at 5 < z < 6
- The mean free path of ionizing photons, lambda(mfp), is a key factor in the photoionization of the intergalactic medium (IGM). At z greater than or similar to 5, however, lambda(mfp) may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of lambda(mfp) that address this bias and extend up to z similar to 6 for the first time. Our measurements at z similar to 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z similar to 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure lambda(mfp) = 9.09(-1.28)(+1.62) proper Mpc and 0.75(-0.45)(+0.65) proper Mpc (68 percent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 fallsThe mean free path of ionizing photons, lambda(mfp), is a key factor in the photoionization of the intergalactic medium (IGM). At z greater than or similar to 5, however, lambda(mfp) may be short enough that measurements towards QSOs are biased by the QSO proximity effect. We present new direct measurements of lambda(mfp) that address this bias and extend up to z similar to 6 for the first time. Our measurements at z similar to 5 are based on data from the Giant Gemini GMOS survey and new Keck LRIS observations of low-luminosity QSOs. At z similar to 6 we use QSO spectra from Keck ESI and VLT X-Shooter. We measure lambda(mfp) = 9.09(-1.28)(+1.62) proper Mpc and 0.75(-0.45)(+0.65) proper Mpc (68 percent confidence) at z = 5.1 and 6.0, respectively. The results at z = 5.1 are consistent with existing measurements, suggesting that bias from the proximity effect is minor at this redshift. At z = 6.0, however, we find that neglecting the proximity effect biases the result high by a factor of two or more. Our measurement at z = 6.0 falls well below extrapolations from lower redshifts, indicating rapid evolution in lambda(mfp) over 5 < z < 6. This evolution disfavours models in which reionization ended early enough that the IGM had time to fully relax hydrodynamically by z = 6, but is qualitatively consistent with models wherein reionization completed at z = 6 or even significantly later. Our mean free path results are most consistent with late reionization models wherein the IGM is still 20 percent neutral at z = 6, although our measurement at z = 6.0 is even lower than these models prefer.…
Author details: | George D. BeckerORCiD, Anson D'Aloisio, Holly M. ChristensonORCiD, Yongda ZhuORCiD, Gábor WorseckORCiD, James S. BoltonORCiD |
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DOI: | https://doi.org/10.1093/mnras/stab2696 |
ISSN: | 0035-8711 |
ISSN: | 1365-2966 |
Title of parent work (English): | Monthly notices of the Royal Astronomical Society |
Subtitle (English): | evidence for rapid evolution near reionization |
Publisher: | Oxford Univ. Press |
Place of publishing: | Oxford |
Publication type: | Article |
Language: | English |
Date of first publication: | 2021/12/18 |
Publication year: | 2021 |
Release date: | 2024/04/25 |
Tag: | cosmology: observations; dark ages; first stars; intergalactic medium; large-scale structure of Universe; quasars: absorption lines; reionization |
Volume: | 508 |
Issue: | 2 |
Number of pages: | 17 |
First page: | 1853 |
Last Page: | 1869 |
Funding institution: | National Science Foundation (NSF)National Science Foundation (NSF)National Research Foundation of Korea [AST-1751404]; NSFNational Science Foundation (NSF) [DGE-1326120]; HST [AR15013.005-A]; NASANational Aeronautics & Space Administration (NASA) [19-ATP19-0191]; STFCUK Research & Innovation (UKRI)Science & Technology Facilities Council (STFC) [ST/T000171/1]; W.M. Keck FoundationW.M. Keck Foundation; ESO telescopes at the La Silla Paranal Observatory [60.A-9024, 084.A-0390, 085.A-0299, 086.A-0162, 086.A-0574, 088.A-0897, 091.C-0934, 097.B-1070, 098.B-0537] |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie |
DDC classification: | 5 Naturwissenschaften und Mathematik / 52 Astronomie / 520 Astronomie und zugeordnete Wissenschaften |
Peer review: | Referiert |