The dynamical influence of the nucleus on the bulge of M31

Massive compact structures in the centres of triaxial stellar systems may subject stars on box orbits to large-angle deflections and thereby disrupt the triaxiality of their parent galaxies. This paper investigates whether the nucleus of M31 can affect the dynamics of the bulge in this way. Photometric models of the nucleus and bulge of M31 are derived from available Stratoscope II and ground-based CCD observations. Rotation measurements at a distance of 2'' from the centre are used to determine a minimum nuclear mass. If the nucleus and bulge each have a constant mass-to-light ratio, the nucleus is sufficiently massive and dense to scatter and disrupt any box orbits in the inner 500 pc of the bulge, implying that the inner bulge could not now be triaxial. (author)