## 5. ResultsThe final seven-component model fits all photometric profiles with
a mean relative error 0.7 per cent, and the rotation curve from
2 kpc to
24 kpc with the relative error 2 per cent. Therefore, the model
is in good agreement with both data sets. The model describes well
also the velocity dispersion data, the distribution of globular
clusters and young stars + gas. The parameters of the final model (the
axial ratio, the harmonic mean radius,
the total mass of the population,
The total luminosity of M 81 is calculated to be the optically visible mass the corresponding ratio The mass-to-light ratio of both disk-like components (disk + flat) together is of all spheroidal components (nucleus+core+bulge+halo) together Total luminosity of the spheroid is . Table 4 presents some descriptive functions calculated for our
final model. where is
the gravitational potential, is the gradient of the gravitational
potential in the radial direction (in the units of
. is the effective
inner mass, defined as a point mass in the centre of the galaxy,
having the same gravitational attraction at The calculated local mass-to-luminosity ratios are given in Fig. 13. A clear difference between the visible and dark matter begins at the distance 11 kpc.
The mass-to-light ratio within the Holmberg radius 19 kpc is . The radius at which the masses of dark matter and visible matter become equal is 26 kpc. These numbers indicate that the DM concentration around M 81 is significantly smaller than around M 31. However, because the extent of DM is larger than for M 31 the ratio of the total mass and visible mass is in both cases nearly the same ( for M 81). © European Southern Observatory (ESO) 1998 Online publication: June 18, 1998 |