The evolution of metallicity and metallicity gradients from z=2.7-0.6
  with KMOS3D
  We present measurements of the [NII]/Ha ratio as a probe of gas-phase oxygen
abundance for a sample of 419 star-forming galaxies at z=0.6-2.7 from the
KMOS3D near-IR multi-IFU survey. The mass-metallicity relation (MZR) is
determined consistently with the same sample selection, metallicity tracer, and
methodology over the wide redshift range probed by the survey. We find good
agreement with long-slit surveys in the literature, except for the low-mass
slope of the relation at z~2.3, where this sample is less biased than previous
samples based on optical spectroscopic redshifts. In this regime we measure a
steeper slope than some literature results. Excluding the AGN contribution from
the MZR reduces sensitivity at the high mass end, but produces otherwise
consistent results. There is no significant dependence of the [NII]/Ha ratio on
SFR or environment at fixed redshift and stellar mass. The IFU data allow
spatially resolved measurements of [NII]/Ha, from which we can infer abundance
gradients for 180 galaxies, thus tripling the current sample in the literature.
The observed gradients are on average flat, with only 15 gradients
statistically offset from zero at >3sigma. We have modelled the effect of
beam-smearing, assuming a smooth intrinsic radial gradient and known seeing,
inclination and effective radius for each galaxy. Our seeing-limited
observations can recover up to 70% of the intrinsic gradient for the largest,
face-on disks, but only 30% for the smaller, more inclined galaxies. We do not
find significant trends between observed or corrected gradients and any stellar
population, dynamical or structural galaxy parameters, mostly in agreement with
existing studies with much smaller sample sizes. In cosmological simulations,
strong feedback is generally required to produce flat gradients at high
redshift.
