The DiskMass Survey. VII. The distribution of luminous and dark matter
  in spiral galaxies
  We present dynamically-determined rotation-curve mass decompositions of 30
spiral galaxies, which were carried out to test the maximum-disk hypothesis and
to quantify properties of their dark-matter (DM) halos. We used measured
vertical velocity dispersions of the disk stars to calculate dynamical mass
surface densities. Together with our atomic and molecular gas mass surface
densities, we derived the stellar mass surface densities, and thus have
absolute measurements of all dominant baryonic components. Using K-band surface
brightness profiles, we calculated the K-band mass-to-light ratio of the
stellar disks (M/L). Our result is consistent with all galaxies in the sample
having equal M/L, with a sample average and scatter of <M/L>=0.31+/-0.07.
Rotation-curves of the baryonic components were calculated from their mass
surface densities, and used with circular-speed measurements to derive the
structural parameters of the DM halos, modeled as either a pseudo-isothermal
sphere (pISO) or an NFW halo. All galaxies in our sample are submaximal, such
that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total
rotation-curves (Fb^{2.2hR}) are less than 0.75. We find this ratio to be
nearly constant between 1-6 hR within individual galaxies. We find a sample
average and scatter of <Fb^{2.2hR}>=0.57+/-0.07, with trends of larger
Fb^{2.2hR} for more luminous and higher-surface-brightness galaxies. To enforce
these being maximal, we need to scale M/L by a factor 3.6 on average. The DM
rotation curves are marginally better fit by a pISO than by an NFW halo. For
the nominal-M/L (submaximal) case, the derived NFW-halo parameters have values
consistent with LCDM N-body simulations, suggesting that the baryonic matter
has only had a minor effect on the DM distribution. In contrast, maximum-M/L
decompositions yield halo concentrations that are too low compared to the LCDM
simulations.
