Dynamical modeling of the stellar nucleus of M 31

Inter–University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune 411 007, India

Corresponding author: N. Sambhus, nbs@iucaa.ernet.in

Received: 13 November 2001
Accepted: 27 February 2002

Abstract

We present stellar dynamical models of the lopsided, double–peaked nucleus of M 31, derived from Hubble Space Telescope (HST) photometry. A Schwarzschild–type method, in conjunction with Richardson–Lucy deconvolution, was employed to construct steadily rotating, hot, stellar disks. The stars orbit a massive dark object, on prograde and retrograde quasi–periodic loop orbits. Our results support Tremaine's eccentric disk model, extended to include a more massive disk, non zero pattern speed (Ω), and different viewing angle. Most of the disk mass populated prograde orbits, with 3.4% on retrograde orbits. The best fits to photometric and kinematic maps were disks with . We speculate on the origins of the lopsidedness, invoking recent work on the linear overstability of nearly Keplerian disks, that possess even a small amount of a counter – rotating component. Accretion of material – no more massive than a globular cluster – onto a preexisting stellar disk, will account for the mass in our retrograde orbits, and could have stimulated the lopsidedness seen in the nucleus of M 31.