Dynamical models of NGC 3115

We present new dynamical models of the S0 galaxy N3115, making use of the available published photometry and kinematics as well as two-dimensional TIGER spectrography. The models are based on a detailed model of the luminosity distribution built using an MGE fit on HST/WFPC2 and ground-based photometric data. We first examined the kinematics in the central 40 arcsec in the light of two-integral f(E,J) models. Jeans equations were used to constrain the mass-to-light ratio, and the central dark mass, the existence of which was suggested by previous studies. The even part of the distribution function was then retrieved via the Hunter & Qian formalism. We thus confirmed that the velocity and dispersion profiles in the central region could be well-fitted with a two-integral model, given the presence of a central dark mass of ~10^9 M_solar. However, no two-integral model could fit the h_3 profile around a radius of about 25 arcsec where the outer disc dominates the surface brightness distribution. Three-integral analytical models were therefore built using a quadratic programming technique. These models showed that three-integral components do indeed provide a reasonable fit to the kinematics, including the higher Gauss-Hermite moments. Again, models without a central dark mass failed to reproduce the observed kinematics in the central arcsec. This clearly supports the presence of a nuclear black hole of at least 6.5x10^8 M_solar in the centre of NGC 3115. These models were finally used to estimate the importance of the dark matter in the outer part of NGC 3115, suggested by the flat stellar rotation curve observed by Capaccioli et al. This study finally points out the difficulty of integrating independently published data in a coherent and consistent way, thus demonstrating the importance of taking into account the details of the instrumental setup and the reduction processes.