Stellar dynamics in the nuclei of M31 and M32 - Evidence for massive black holes?

Abstract

We present new kinematic data based on the calcium IR triplet lines that define rotation and velocity dispersion profiles for the nuclei of M31 and M32 with high accuracy. These data confirm earlier work by Dressler, Kormendy, and Tonry which indicated rapid rotation and high-velocity dispersions in the central few parsecs of both systems. Stellar dynamical models which allow for anisotropic velocity dispersions have been constructed using the maximum entropy technique. These three-dimensional models have been projected in the plane of the sky and convolved with the seeing profile and finite slit width using a new technique that constructs synthetic spectra. These spectra are then analyzed in exactly the same manner as the real data, thus guaranteeing that the response of the Fourier program to multiple-temperature components and steep rotation gradients has been properly taken into account. We conclude that constant M/L models are ruled out for both systems, regardless of the degree of anisotropy of the velocity dispersions. The most straightforward interpretation is that M31 and M32 harbor central black holes of ~3-7 x 10^7^ and ~8 x 10^6^ solar masses, respectively. The case of M31 is somewhat complicated by a curious separation of the kinematic center from the luminosity peak, but none of our explanations for this phenomenon weaken the interpretation that a central black hole is present. The presence of black holes in these two neighboring galaxies with spheroidal stellar components suggests that black holes of up to 10^9^ M_sun_, favored in many quasar models, may be present in galaxies with the largest spheroidal components.