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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|
Fynbo, J. P. U.
Hartoog, O. E.
Perley, D. A.
Vergani, S. D.
Afonso, P. M. J.
de Ugarte Postigo, A.
Graham, J. F.
Kann, D. A.
Levan, A. J.
Guelbenzu, A. N.
Vreeswijk, P. M.
Watson, D. J.
|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.|
|Rights:||Reproduced with permission from Astronomy & Astrophysics, © ESO. Deposited with reference to the publisher’s open access archiving policy, available at http://www.aanda.org/author-information/copyright|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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|1505.06743v3.pdf||Post-review (final submitted)||3.51 MB||Adobe PDF||View/Open|
|aa25561-14.pdf||Published (publisher PDF)||3.31 MB||Adobe PDF||View/Open|
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