Spatially resolved optical IFU spectroscopy of the inner superwind of
  NGC 253
  [abridged] We present optical integral field unit observations (VLT/VIMOS-IFU
and WIYN/SparsePak), and associated archival deep Halpha imaging (ESO 2.2m
WFI), of the nearby starburst galaxy NGC253. With VIMOS we observed the nuclear
region and southern superwind outflow in detail with five pointings, and with
SparsePak we observed two partially overlapping regions covering the central
disk and northern halo. The high signal-to-noise of the data and spectral
resolution (80-90 km/s) enable us to accurately decompose the emission line
profiles into multiple components.
  The combination of these datasets, together with information available in the
literature, has allowed us to study the starburst-driven superwind in great
detail. We investigate the known minor axis outflow cone, which is well-defined
in the Halpha imaging and kinematics between r=280-660 pc from the nucleus.
Kinematic modelling indicates a wide opening angle (~60 deg), an inclination
consistent with the disk, and deprojected outflow speeds of a few 100 km/s that
increase with distance above the plane. The [NII]/Halpha and [SII]/Halpha line
ratio maps imply that a significant fraction of the wind optical emission lines
arise from shocked gas. From the kinematics, the cone appears partially closed
in at least one place, and very broad Halpha line widths (>400 km/s FWHM)
suggest there is material filling the cone in some regions. Extrapolation of
the cone to its apex shows it is not centred on the starburst nucleus,
suggesting the wind is deflected and collimated by the dense circumnuclear
material. We discuss the implications of these findings on our understanding of
the origins and evolution of the superwind. The lack of an obvious connection
between the inner (r<1 kpc) Halpha and X-ray bright outflow cone and the
large-scale (r<10 kpc) X-ray "horns" is also discussed.
