Dark matter in spiral galaxies and the Arimoto-Jablonka photometric model

We use the recent stellar population synthesis models by Arimoto and Jablonka (1991), which by introducing the bulge into the calculation of galaxy masses mark a significant improvement over previous one-component models, to show that low-luminosity spiral galaxies have a higher dark matter fraction within the optical radius than high-luminosity spirals. In fact, the derived dark-to-visible mass ratio increases with decreasing luminosity, approximately as L(B)(-1/2). This conclusion agrees with previous results based on dynamical disc/halo decompositions of galaxy rotation curves (e.g. Persic and Salucci 1988). On the other hand, we do not find any strong trend between dark matter content and galaxy B-V colours, although we cannot exclude a weak one. Our results agree with Jablonka and Arimoto's (1992) conclusion that colours are not a primary indicator of the dark matter content of spiral galaxies. Instead, we confirm that the luminosity is a fundamental indicator of the dark mass fraction of spiral galaxies.