  Major gas-rich mergers of galaxies are expected to play an important role in
triggering and fuelling luminous AGN. We present deep multi-band (u/r/z)
imaging and long slit spectroscopy of four double-peaked [OIII] emitting AGN, a
class of objects associated with either kcp-separated binary AGN or final stage
major mergers, though AGN with complex narrow-line regions are known
contaminants. Such objects are of interest since they represent the onset of
AGN activity during the merger process. Three of the objects studied have been
confirmed as major mergers using near-infrared imaging, one is a confirmed
X-ray binary AGN. All AGN are luminous and have redshifts of 0.1 < z < 0.4.
Deep r-band images show that a majority (3/4) of the sources have disturbed
host morphologies and tidal features, while the remaining source is
morphologically undisturbed down to low surface brightness limits. The lack of
morphological disturbances in this galaxy despite the fact that is is a close
binary AGN suggests that the merger of a binary black hole can take longer than
~1 Gyr. The narrow line regions (NLRs) have large sizes (10 kpc < r < 100 kpc)
and consist of compact clumps with considerable relative velocities (~ 200-650
km/s). We detect broad, predominantly blue, wings with velocities up to ~1500
km/s in [OIII], indicative of powerful outflows. The outflows are compact (<5
kpc) and co-spatial with nuclear regions showing considerable reddening,
consistent with enhanced star formation. One source shows an offset between gas
and stellar kinematics, consistent with either a bipolar flow or a
counter-rotating gas disk. We are not able to unambiguously identify the
sources as binary AGN using our data, X-ray or radio data is required for an
unambiguous identification. However, the data still yield interesting results
for merger triggering of AGN and time-scales of binary black hole mergers.
