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Title: The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium
Authors: Tanvir, NR
Fynbo, JPU
Postigo, ADU
Japelj, J
Wiersema, K
Malesani, D
Perley, DA
Levan, AJ
Selsing, J
Cenko, SB
Kann, DA
Milvang-Jensen, B
Berger, E
Cano, Z
Chornock, R
Covino, S
Cucchiara, A
D'Elia, V
Goldoni, P
Gomboc, A
Heintz, KE
Hjorth, J
Izzo, L
Jakobsson, P
Kaper, L
Kruehler, T
Laskar, T
Myers, M
Piranomonte, S
Pugliese, G
Sanchez-Ramirez, R
Schulze, S
Sparre, M
Stanway, ER
Tagliaferri, G
Thoene, CC
Vergani, S
Vreeswijk, PM
Wijers, RAMJ
Watson, D
Xu, D
First Published: 20-Dec-2018
Publisher: Oxford University Press (OUP), Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2019, 483(4), pp. 5380–5408
Abstract: Whether stars could have driven the reionization of the intergalactic medium depends critically on the proportion of ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst (GRB) afterglows can be used to estimate the opacity to extreme ultraviolet (EUV) radiation along the lines-of-sight to the bursts. Assuming that long-duration GRBs trace the locations of the massive stars dominating EUV production, the average escape fraction of ionizing radiation can be calculated independently of galaxy size or luminosity. Here we present a compilation of H I column density (NH I) measures for 140 GRBs in the range 1.6 <z< 6.7. Although the sample is heterogeneous, in terms of spectral resolution and signal-to-noise ratio, fits to the Ly α absorption line provide robust constraints on NH I, even for spectra of insufficient quality for other purposes. Thus we establish an escape fraction at the Lyman limit of fesc ≈ 0.005, with a 98 per cent confidence upper limit of fesc ≈ 0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget at z < 5. At higher redshifts firm conclusions are limited by the small size of the GRB sample (7/140), but any decline in average H I column density seems to be modest. We also find no significant correlation of NH I with galaxy UV luminosity or host stellar mass. We discuss in some detail potential biases and argue that, while not negligible, systematic errors in fesc are unlikely to be more than a factor ∼2 in either direction, and so would not affect the primary conclusions. Given that many GRB hosts are low-metallicity dwarf galaxies with high specific star-formation rates, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the Universe.
DOI Link: 10.1093/mnras/sty3460
eISSN: 1538-3881
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2018, Oxford University Press (OUP), Royal Astronomical Society. Deposited with reference to the publisher’s open access archiving policy. (
Description: Spectra presented in the appendix will be made available in the GRBspec data base (de Ugarte Postigo et al. 2014a).
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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