Global modal analysis of disk galaxies : application to an SO galaxy NGC 3115.

The global modal analysis of oscillations is applied to a series of models for NGC 3115. All the models in this series are consistent with the observed rotation curve and the observed velocity dispersion curve of NGC 3115 but have different halo mass fractions. The apparent lack of any spiral structure in this galaxy implies that the disk is stable, and this requirement gives a loose lower limit for the halo mass fraction of 30 percent of the total mass. This estimate is independent of photometric evaluation, and the result, although modest, is consistent with the photometric estimate.