Dark matter in spiral galaxies. II - Galaxies with H I rotation curves

Abstract

Luminosity profiles and rotation curves for 16 galaxies are analyzed to study the light and mass distribution in each galaxy. The mass distribution is modeled as the sum of bulge and disk stellar components and a dark halo. Mass/light ratios of the bulge and disk and two parameters to describe the halo are derived for each galaxy. In contrast to the situation where only optical rotation curves are available, all galaxies with H I rotation curves show evidence for dark matter. Although the relative contributions of stellar and dark matter are not well determined, the stellar component is usually close (70% or more) to its maximum possible value (the maximum-disk solution). The shapes of the luminosity profiles and rotation curves are correlated. The nature of the disk-halo conspiracy required to produce the rather featureless rotation curves is examined. As an alternative to the dark matter hypothesis, Milgrom's theory of modified Newtonian dynamics is also used to analyze the rotation curves.