Maximum disk mass models for spiral galaxies

We present axisymmetric maximum disk mass models for a sample of 74 spiral galaxies taken from the southern sky Fabry-Perot Tully-Fisher survey by Sch ommer et al. The sample contains galaxies spanning a large range of morphol ogies and having rotation widths from 180 km s(-1) to 680 km s(-1) For each galaxy we have an I-band image and a two-dimensional H alpha velocity fiel d. We decompose the disk and bulge by fitting models directly to the I-band image. This method utilizes both the distinct surface brightness profiles and shapes of the projected disk and bulge in the galaxy images. The lumino sity profiles and rotation curves are derived using consistent centers, pos ition angles, and inclinations derived from the photometry and velocity map s. The distribution of mass is modeled as a sum of disk and bulge component s with distinct, constant mass-to-light ratios. No dark matter halo is incl uded in the fits. The models reproduce the overall structure of the rotatio n curves in the majority of galaxies, providing good fits to galaxies that exhibit pronounced structural differences in their surface brightness profi les. Of galaxies for which the rotation curve is measured to R-23.5 or beyo nd 75% are well fitted by a mass-traces-light model for the entire region w ithin R-23.5. The models for about 20% of the galaxies do not fit well; the failure of most of these models is traced directly to nonaxisymmetric stru ctures, primarily bars but also strong spiral arms. The median I-band MIL o f the disk plus bulge is 2.4 +/- 0.9 h(75) in solar units, consistent with normal stellar populations. These results require either that the mass of d ark matter within the optical disk of spiral galaxies is small or that its distribution is very precisely coupled to the distribution of luminous matt er.