Nebular Excitation in z~2 Star-forming Galaxies from the SINS and LUCI
  Surveys: The Influence of Shocks and AGN
  Based on high-resolution, spatially resolved data of 10 z~2 star-forming
galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies,
we probe the excitation properties of high-z galaxies and the impact of active
galactic nuclei (AGN), shocks and photoionization. We explore how these
spatially-resolved line ratios can inform our interpretation of integrated
emission line ratios obtained at high redshift. Many of our galaxies fall in
the `composite' region of the z~0 [NII]/Ha versus [OIII]/Hb diagnostic (BPT)
diagram, between star-forming galaxies and those with AGN. Based on our
resolved measurements, we find that some of these galaxies likely host an AGN,
while others appear to be affected by the presence of shocks possibly caused by
an outflow or from enhanced ionization parameter as compared with HII regions
in normal local star-forming galaxies. We find that the Mass-Excitation (MEx)
diagnostic, which separates purely star-forming and AGN hosting local galaxies
in the [OIII]/Hb versus stellar mass plane, does not properly separate z~2
galaxies classified according to the BPT diagram. However, if we shift the
galaxies based on the offset between the local and z~2 mass-metallicity
relation (i.e. to the mass they would have at z~0 with the same metallicity),
we find better agreement between the MEx and BPT diagnostics. Finally, we find
that metallicity calibrations based on [NII]/Ha are more biased by shocks and
AGN at high-z than the [OIII]/Hb/[NII]/Ha calibration.
