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Title: GRB hosts through cosmic time VLT/X-Shooter emission-line spectroscopy of 96 gamma-ray-burst-selected galaxies at 0.1 < z < 3.6
Authors: Kruehler, T.
Malesani, D.
Fynbo, J. P. U.
Hartoog, O. E.
Hjorth, J.
Jakobsson, P.
Perley, D. A.
Rossi, A.
Schady, P.
Schulze, S.
Tanvir, Nial
Vergani, S. D.
Wiersema, K.
Afonso, P. M. J.
Bolmer, J.
Cano, Z.
Covino, S.
D'Elia, V.
de Ugarte Postigo, A.
Filgas, R.
Friis, M.
Graham, J. F.
Greiner, J.
Goldoni, P.
Gomboc, A.
Hammer, F.
Japelj, J.
Kann, D. A.
Kaper, L.
Klose, S.
Levan, A. J.
Leloudas, G.
Milvang-Jensen, B.
Guelbenzu, A. N.
Palazzi, E.
Pian, E.
Piranomonte, S.
Sanchez-Ramirez, R.
Savaglio, S.
Selsing, J.
Tagliaferri, G.
Vreeswijk, P. M.
Watson, D. J.
Xu, D.
First Published: 21-Sep-2015
Publisher: EDP Sciences
Citation: Astronomy and Astrophysics, 2015, 581
Abstract: We present data and initial results from VLT/X-Shooter emission-line spectroscopy of 96 galaxies selected by long γ-ray bursts (GRBs) at 0.1 <z< 3.6, the largest sample of GRB host spectra available to date. Most of our GRBs were detected by Swift and 76% are at 0.5 <z< 2.5 with a median z [Subscript: med] ~ 1.6. Based on Balmer and/or forbidden lines of oxygen, nitrogen, and neon, we measure systemic redshifts, star formation rates (SFR), visual attenuations (AV), oxygen abundances (12 + log (O/H)), and emission-line widths (σ). We study GRB hosts up to z ~ 3.5 and find a strong change in their typical physical properties with redshift. The median SFR of our GRB hosts increases from SFR[Subscript: med] ~ 0.6 M[Subscript: ⊙] yr [Superscript: -1] at z ~ 0.6 up to SFR[Subscript: med] ~ 15 M [Subscript: ⊙] yr[Superscript: -1] at z ~ 2. A higher ratio of [O iii]/[O ii]  at higher redshifts leads to an increasing distance of GRB-selected galaxies to the locus of local galaxies in the Baldwin-Phillips-Terlevich diagram. There is weak evidence for a redshift evolution in AV and σ, with the highest values seen at z ~ 1.5 (AV) or z ~ 2 (σ). Oxygen abundances of the galaxies are distributed between 12 + log (O/H) = 7.9 and 12 + log (O/H) = 9.0 with a median 12 + log (O/H) [Subscript: med] ~ 8.5. The fraction of GRB-selected galaxies with super-solar metallicities is ~20% at z< 1 in the adopted metallicity scale. This is significantly less than the fraction of total star formation in similar galaxies, illustrating that GRBs are scarce in high metallicity environments. At z ~ 3, sensitivity limits us to probing only the most luminous GRB hosts for which we derive metallicities of Z ≲ 0.5 Z [Subscript: ⊙] . Together with a high incidence of Z ~ 0.5 Z [Subscript: ⊙] galaxies at z ~ 1.5, this indicates that a metallicity dependence at low redshift will not be dominant at z ~ 3. Significant correlations exist between the hosts’ physical properties. Oxygen abundance, for example, relates to AV (12 + log (O/H) ∝ 0.17·AV), line width (12 + log (O/H) ∝ σ [Superscript: 0.6] ), and SFR (12 + log (O/H) ∝ SFR [Superscript: 0.2]). In the last two cases, the normalization of the relations shift to lower metallicities at z> 2 by ~0.4 dex. These properties of GRB hosts and their evolution with redshift can be understood in a cosmological context of star-forming galaxies and a picture in which the hosts’ properties at low redshift are influenced by the tendency of GRBs to avoid the most metal-rich environments.
DOI Link: 10.1051/0004-6361/201425561
ISSN: 0004-6361
eISSN: 1432-0746
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Reproduced with permission from Astronomy & Astrophysics, © ESO. Deposited with reference to the publisher’s open access archiving policy, available at
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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