Resolving the Disc-Halo Degeneracy II: NGC 6946
  The mass-to-light ratio (M/L) is a key parameter in decomposing galactic
rotation curves into contributions from the baryonic components and the dark
halo of a galaxy. One direct observational method to determine the disc M/L is
by calculating the surface mass density of the disc from the stellar vertical
velocity dispersion and the scale height of the disc. Usually, the scale height
is obtained from near-IR studies of edge-on galaxies and pertains to the older,
kinematically hotter stars in the disc, while the vertical velocity dispersion
of stars is measured in the optical band and refers to stars of all ages (up to
~10 Gyr) and velocity dispersions. This mismatch between the scale height and
the velocity dispersion can lead to underestimates of the disc surface density
and a misleading conclusion of the sub-maximality of galaxy discs. In this
paper we present the study of the stellar velocity dispersion of the disc
galaxy NGC 6946 using integrated star light and individual planetary nebulae as
dynamical tracers. We demonstrate the presence of two kinematically distinct
populations of tracers which contribute to the total stellar velocity
dispersion. Thus, we are able to use the dispersion and the scale height of the
same dynamical population to derive the surface mass density of the disc over a
radial extent. We find the disc of NGC 6946 to be closer to maximal with the
baryonic component contributing most of the radial gravitational field in the
inner parts of the galaxy (Vmax(bar) = 0.76($\pm$0.14)Vmax).
