1. VLT/X-Shooter emission-line spectroscopy of 96 -ray-burst-selected galaxies at 0.1 < z < 3.6.
- Author
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Krühler, T., Malesani, D., Fynbo, J. P. U., Hartoog, O. E., Hjorth, J., Jakobsson, P., Perley, D. A., Rossi, A., Schady, P., Schulze, S., Tanvir, N. R., Vergani, S. D., Wiersema, K., Afonso, P. M. J., Bolmer, J., Cano, Z., Covino, S., D'Elia, V., de Ugarte Postigo, A., and Filgas, R.
- Subjects
EMISSION-line galaxies ,BALMER series ,REDSHIFT ,STAR formation ,COSMIC abundances ,GAMMA ray bursts - 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
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 (A V ), 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 SFRmed ~ 0.6 M⊙ yr-1 at z ~ 0.6 up to SFRmed ~ 15 M⊙ yr-1 at z ~ 2. A higher ratio of [OIII ]/[OII ] 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)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⊙ . 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 AV (12 + log (O/H) ∝ 0.17⋅AV ), line width (12 + log(O/H) ∝ σ0.6 ), and SFR (12 + log(O/H) ∝ SFR0.2 ). 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. [ABSTRACT FROM AUTHOR]- Published
- 2015
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