The low-extinction afterglow in the solar-metallicity host galaxy of GRB
  110918A
  Galaxies selected through long gamma-ray bursts (GRBs) could be of
fundamental importance when mapping the star formation history out to the
highest redshifts. Before using them as efficient tools in the early Universe,
however, the environmental factors that govern the formation of GRBs need to be
understood. Metallicity is theoretically thought to be a fundamental driver in
GRB explosions and energetics, but is still, even after more than a decade of
extensive studies, not fully understood. This is largely related to two
phenomena: a dust-extinction bias, that prevented high-mass and thus likely
high-metallicity GRB hosts to be detected in the first place, and a lack of
efficient instrumentation, that limited spectroscopic studies including
metallicity measurements to the low-redshift end of the GRB host population.
The subject of this work is the very energetic GRB 110918A, for which we
measure one of the largest host-integrated metallicities, ever, and the highest
stellar mass for z<1.9. This presents one of the very few robust metallicity
measurements of GRB hosts at z~1, and establishes that GRB hosts at z~1 can
also be very metal rich. It conclusively rules out a metallicity cut-off in GRB
host galaxies and argues against an anti-correlation between metallicity and
energy release in GRBs.
