Basic parameters of dark halos in late-type spirals.

The mass distribution in the Sm galaxy NGC 3109 and the Sd galaxies NGC 7793, NGC 247, and NGC 300 in the Sculptor Group is investigated theoretically by means of numerical simulations, assuming that the mass/light ratios of the galactic disks are constant. The results are presented in tables and graphs and characterized. The dark components required to reproduce the rotation curves of NGC 247, NGC 300, and NGC 3109 are modeled as isothermal spheres, and the lower limits of the core radii and one-component velocity dispersions are estimated as 10-22 kpc and 40-100 km/s, respectively, corresponding to a central density range of 0.002-0.004 solar mass/cu pc. The data are found to be consistent with population models with self-gravitating inner disks and with the assumption of a luminosity-independent Holmberg-radius halo/disk mass ratio.