P-MaNGA: Emission Lines Properties - Gas Ionisation and Chemical
  Abundances from Prototype Observations
  MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a SDSS-IV
survey that will obtain spatially resolved spectroscopy from 3600 \AA\ to 10300
\AA\ for a representative sample of over 10000 nearby galaxies. In this paper
we present the analysis of nebular emission line properties in 14 galaxies
obtained with P-MaNGA, a prototype of the MaNGA instrument. Using spatially
resolved diagnostic diagrams we find extended star formation in galaxies that
are centrally dominated by Seyfert/LINER-like emission, which illustrates that
galaxy characterisations based on single fibre spectra are necessarily
incomplete. We observe extended LINER-like emission (up to $\rm 1 R_{e}$) in
three galaxies. We make use of the $\rm EW(H \alpha)$ to argue that the
observed emission is consistent with ionisation from hot evolved stars. We
derive stellar population indices and demonstrate a clear correlation between
$\rm D_n(4000)$ and $\rm EW(H \delta_A)$ and the position in the ionisation
diagnostic diagram: resolved galactic regions which are ionised by a
Seyfert/LINER-like radiation field are also devoid of recent star formation and
host older and/or more metal rich stellar populations. We also detect
extraplanar LINER-like emission in two highly inclined galaxies, and identify
it with diffuse ionised gas. We investigate spatially resolved metallicities
and find a positive correlation between metallicity and star formation rate
(SFR) surface density. We study the relation between N/O vs O/H on resolved
scales. We find that, at given N/O, regions within individual galaxies are
spread towards lower metallicities, deviating from the sequence defined by
galactic central regions as traced by Sloan $3''$ fibre spectra. We suggest
that the observed dispersion can be a tracer for gas flows in galaxies: infalls
of pristine gas and/or the effect of a galactic fountain.
