Modeling the Mass Distribution in Spiral Galaxies

Abstract

We use deep r-band photometry and Halpha rotation curves for a sample of 290 late-type spirals to model their mass distribution within the optical radius. We examine luminosity profile decompositions into bulge and disk carefully and confirm that bulge light is best modeled by a seeing-convolved exponential profile. The optical rotation curves are well-reproduced with a combination of bulge and "maximum" disk components only. No dark halo is needed. The disk mass-to-light ratios (M/L's) correlate with the "size" of galaxies, as measured by mass, luminosity, or disk scale length. Correcting for this scale effect yields a narrow distribution of intrinsic M/L's for this galaxy population. By combining these models with HI data for other samples, we confirm that the luminous mass fraction increases with galaxy "size".