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Lyman continuum leakage in faint star-forming galaxies at redshift z = 3−3.5 probed by gamma-ray bursts

Lyman continuum leakage in faint star-forming galaxies at redshift z = 3−3.5 probed by gamma-ray bursts

Title: Lyman continuum leakage in faint star-forming galaxies at redshift z = 3−3.5 probed by gamma-ray bursts
Author: Vielfaure, J.-B.
Vergani, S. D.
Japelj, J.
Fynbo, J. P. U.
Gronke, M.
Elm Heintz, Kasper   orcid.org/0000-0002-9389-7413
Malesani, D. B.
Petitjean, P.
Tanvir, N. R.
D’Elia, V.
... 16 more authors Show all authors
Date: 2020-09
Language: English
Scope: A30
University/Institute: Háskóli Íslands
University of Iceland
School: Verkfræði- og náttúruvísindasvið (HÍ)
School of Engineering and Natural Sciences (UI)
Department: Raunvísindastofnun (HÍ)
Science Institute (UI)
Series: Astronomy & Astrophysics;641
ISSN: 0004-6361
1432-0746 (eISSN)
DOI: 10.1051/0004-6361/202038316
Subject: First stars; Galaxies: evolution; Galaxies: high-redshift; Gamma-ray burst: general; Intergalactic medium; Reionization; Stjarneðlisfræði; Vetrarbrautir
URI: https://hdl.handle.net/20.500.11815/2239

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Vielfaure, J.-B., Vergani, S.D., Japelj, J., Fynbo, J.P.U., Gronke, M., Heintz, K.E., Malesani, D.B., 2020. Lyman continuum leakage in faint star-forming galaxies at redshift z=3-3.5 probed by gamma-ray bursts. Astronomy & Astrophysics.. doi:10.1051/0004-6361/202038316


Context. The identification of the sources that reionized the Universe and their specific contribution to this process are key missing pieces of our knowledge of the early Universe. Faint star-forming galaxies may be the main contributors to the ionizing photon budget during the epoch of reionization, but their escaping photons cannot be detected directly due to inter-galactic medium opacity. Hence, it is essential to characterize the properties of faint galaxies with significant Lyman continuum (LyC) photon leakage up to z ∼ 4 to define indirect indicators allowing analogs to be found at the highest redshift. Aims. Long gamma-ray bursts (LGRBs) typically explode in star-forming regions of faint, star-forming galaxies. Through LGRB afterglow spectroscopy it is possible to detect directly LyC photons. Our aim is to use LGRBs as tools to study LyC leakage from faint, star-forming galaxies at high redshift. Methods. Here we present the observations of LyC emission in the afterglow spectra of GRB 191004B at z = 3:5055, together with those of the other two previously known LyC-leaking LGRB host galaxies (GRB 050908 at z = 3:3467, and GRB 060607A at z = 3:0749), to determine their LyC escape fraction and compare their properties. Results. From the afterglow spectrum of GRB 191004B we determine a neutral hydrogen column density at the LGRB redshift of log(NHI/cm-2) = 17:2±0:15, and negligible extinction (AV = 0:03±0:02 mag). The only metal absorption lines detected are C iv and Si iv. In contrast to GRB 050908 and GRB 060607A, the host galaxy of GRB 191004B displays significant Lyman-alpha (Lya) emission. From its Lya emission and the nondetection of Balmer emission lines we constrain its star-formation rate (SFR) to 1 = SFR = 4:7 M yr-1. We fit the Lya emission with a shell model and find parameters values consistent with the observed ones. The absolute (relative) LyC escape fractions we find for GRB 191004B, GRB 050908 and GRB 060607A are of 0:35+0:10-0:11 (0:43+-0 0:12 13), 0:08+-0 0:05 04 (0:08+-0 0:05 04) and 0:20+-0 0:05 05 (0:45+-0 0:15 15), respectively. We compare the LyC escape fraction of LGRBs to the values of other LyC emitters found from the literature, showing that LGRB afterglows can be powerful tools to study LyC escape for faint high-redshift star-forming galaxies. Indeed we could push LyC leakage studies to much higher absolute magnitudes. The host galaxies of the three LGRBs presented here have all M1600 >-19:5 mag, with the GRB 060607A host at M1600 >-16 mag. LGRB hosts may therefore be particularly suitable for exploring the ionizing escape fraction in galaxies that are too faint or distant for conventional techniques. Furthermore, the time involved is minimal compared to galaxy studies. © 2020 Author(s).


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Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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