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GRB hosts through cosmic time: VLT/X-Shooter emission-line spectroscopy of 96 γ -ray-burst-selected galaxies at 0.1 < z < 3.6

Krühler, T and Malesani, D and Fynbo, JPU and Hartoog, OE and Hjorth, J and Jakobsson, P and Perley, DA and Rossi, A and Schady, P and Schulze, S and Tanvir, NR and Vergani, SD and Wiersema, K and Afonso, PMJ and Bolmer, J and Cano, Z and Covino, S and D'Elia, V and De Ugarte Postigo, A and Filgas, R and Friis, M and Graham, JF and Greiner, J and Goldoni, P and Gomboc, A and Hammer, F and Japelj, J and Kann, DA and Kaper, L and Klose, S and Levan, AJ and Leloudas, G and Milvang-Jensen, B and Nicuesa Guelbenzu, A and Palazzi, E and Pian, E and Piranomonte, S and Sánchez-Ramírez, R and Savaglio, S and Selsing, J and Tagliaferri, G and Vreeswijk, PM and Watson, DJ and Xu, D (2015) GRB hosts through cosmic time: VLT/X-Shooter emission-line spectroscopy of 96 γ -ray-burst-selected galaxies at 0.1 < z < 3.6. Astronomy & Astrophysics, 581. ISSN 1432-0746

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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 zmed ∼ 1.6. Based on Balmer and/or forbidden lines of oxygen, nitrogen, and neon, we measure systemic redshifts, star formation rates (SFR), visual attenuations (A<inf>V</inf>), 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<inf>med</inf> ∼ 0.6 M yr<sup>-1</sup> at z ∼ 0.6 up to SFR<inf>med</inf> ∼ 15 M yr<sup>-1</sup> 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 A<inf>V</inf> and σ, with the highest values seen at z ∼ 1.5 (A<inf>V</inf>) 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)<inf>med</inf> ∼ 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. Together with a high incidence of Z ∼ 0.5 Z 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 A<inf>V</inf> (12 + log (O/H) 0.17·A<inf>V</inf>), line width (12 + log (O/H) σ<sup>0.6</sup>), and SFR (12 + log (O/H) SFR<sup>0.2</sup>). 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. © ESO, 2015.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
Date Deposited: 21 Feb 2017 12:06
Last Modified: 09 Sep 2017 18:22
DOI or Identification number: 10.1051/0004-6361/201425561
URI: http://researchonline.ljmu.ac.uk/id/eprint/5686

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