The Gaia-ESO Survey: the N/O abundance ratio in the Milky Way
  The abundance ratio N/O is a useful tool to study the interplay of galactic
processes, e.g. star formation efficiency, time-scale of infall and outflow
loading factor We aim to trace log(N/O) versus [Fe/H] in the Milky Way and to
compare it with a set of chemical evolution models to understand the role of
infall, outflow and star formation efficiency in the building-up of the
Galactic disc. We use the abundances from idr2-3, idr4, idr5 data releases of
the Gaia-ESO Survey both for Galactic field and open cluster stars.We determine
membership and average composition of open clusters and we separate thin and
thick disc field stars.We consider the effect of mixing in the abundance of N
in giant stars. We compute a grid of chemical evolution models, suited to
reproduce the main features of our Galaxy, exploring the effects of the star
formation efficiency, the infall time-scale and the differential outflow. With
our samples, we map the metallicity range -0.6<[Fe/H]<0.3 with a corresponding
-1.2<log(N/O)<-0.2, where the secondary production of N dominates. Thanks to
the wide range of Galactocentric distances covered by our samples, we can
distinguish the behaviour of log(N/O) in different parts of the Galaxy. Our
spatially resolved results allow us to distinguish differences in the evolution
of N/O with Galactocentric radius. Comparing the data with our models, we can
characterise the radial regions of our Galaxy. A shorter infall time-scale is
needed in the inner regions, while the outer regions need a longer infall
time-scale, coupled with a higher star formation efficiency. We compare our
results with nebular abundances obtained in MaNGA galaxies, finding in our
Galaxy a much wider range of log(N/O) than in integrated observations of
external galaxies of similar stellar mass, but similar to the ranges found in
studies of individual H ii regions.
