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Fig. 4


Comparison of the BAT6 sample hosts (circles) to the average mass-metallicity relations at different redshifts. a) Metallicities are presented in the Maiolino et al. (2008) calibration. Overplotted are the models fitted to star-forming galaxy populations at different mean redshifts in the range of z ~ 0.07–4 (M09; Mannucci et al. 2009). As a comparison sample (stars) we plot the incomplete sample compiled by Mannucci et al. (2011) over 0.3 <z< 1. b) Metallicities are presented in the Kobulnicky & Kewley (2004) calibration. Both upper and lower branch solution are plotted in cases where one solution cannot be obtained – in these cases the two values are connected with a dashed line and the lower branch solution is plotted within a square for clarity. For comparison we also include the incomplete sample of LGRB hosts from Levesque et al. (2010a) (stars) 0.3 <z< 1. Lines represent fitted relations for galaxies at z = 0.3 and 0.8 (Zahid et al. 2013a). The extrapolation towards low stellar masses is indicated by dashed lines. Lower panels show the difference between the LGRB metallicities (0.3 <z< 1) and the median relations at redshift a) 0.7 and b) 0.8, respectively. Vertical grey lines in the lower panels mark the mass below which the two relations have been extrapolated. Errors of the comparison samples are not plotted in the upper panels for clarity, but are taken into account when calculating the difference from median relations (both errors in mass and metallicity are accounted for). The dotted horizontal lines in the lower panels show the intrinsic dispersion of the median relations – we assume a typical value of ± 0.2 dex.

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