The Kinematics of Early Type Galaxies

Abstract

Recent observations of the kinematics of the central regions of M 31, M 32 and NGC 4594 at high spatial resolution have revealed steep central velocity gradients and high velocity dispersions that have been interpreted as indicating the presence of large central masses. Axisymmetric, constant mass-to-light ratio models can account for the steep rise in velocity dispersion found in these galaxies if the stellar orbits become increasingly radial towards the center, but cannot simultaneously reproduce the steep velocity gradients observed. When central point masses of 106–9 M ⊙ are added to these models, both the rotation and dispersion profile can be fit simultaneously. Alternative explainations for the observed behavior need to be investigated. For example, in the case of M 31, a nuclear bar viewed end-on has been suggested to account for the observations. In addition, we need to understand how the presence of a black hole would effect the distribution of the orbits of the stars, and what observable effects might be generated.