Integral Field Spectroscopy of HII region complexes. The outer disk of
  NGC 6946
  Integral Field Spectroscopy obtained with PPak and the 3.5m telescope at the
Calar Alto Observatory has been used to study an outer HII region complex in
the well studied galaxy NGC 6946. This technique provides detailed maps of the
region in different emission lines yielding spatially resolved information
about the physical properties of the gas. The configuration was chosen to cover
the whole spectrum from 3600 up to 10000 A. We selected four luminous knots, to
perform a detailed integrated spectroscopic analysis of these structures and of
the whole PPak field-of-view (FOV). For all the knots the electron density has
been found to be very similar and below 100 cm^-3. The [OIII] electron
temperature was measured in knots A, B, C and in the integrated PPak-field, and
was found to be around 8000 K. The temperatures of [OII] and [SIII] were
estimated in the four cases. The elemental abundances computed from the "direct
method" are typical of high metallicity disk HII regions, with a mean value of
12+log(O/H)= 8.65, comparable to what has been found in this galaxy by other
authors for regions at similar galactocentric distance. Therefore, a remarkable
abundance uniformity is found despite the different excitations found
throughout the nebula. Wolf-Rayet features have been detected in three of the
knots, leading to a derived total number of WR stars of 125, 22 and 5, for
knots A, C and B, respectively. The integrated spectrum of the whole PPak FOV
shows high excitation and a relatively evolved age which does not correspond to
the individual knot evolutionary stages. Some effects associated to the loss of
spatial resolution could also be evidenced by the higher ionising temperature
that is deduced from the eta' parameter measured in the integrated PPak
spectrum with respect to that of the individual knots.
