SDSS-IV MaNGA: Variations in the N/O -- O/H relation bias metallicity
  gradient measurements
  In this paper we use strong line calibrations of N/O and O/H in MaNGA spaxel
data to explore the systematics introduced by variations in N/O on various
strong-line metallicity diagnostics. We find radial variations in N/O at fixed
O/H which correlate with total galaxy stellar-mass; and which can induce $\sim
40 \%$ systematic uncertainties in oxygen abundance gradients when
nitrogen-dependent abundance calibrations are used. Empirically, we find that
these differences are associated with variation in the local star formation
efficiency, as predicted by recent chemical evolution models for galaxies, but
we cannot rule out other processes such as radial migration and the accretion
of passive dwarf galaxies also playing a role.
