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K.V. Johnston (Wesleyan Univ.), P.I. Choi, P. Guhathakurta (UC Santa Cruz)
We have carried out a suite of N-body simulations designed to investigate the tidal disruption of dwarf satellite galaxies by their parent galaxy. The parent galaxy is modelled as a static, axisymmetric, three-component (disk, bulge, halo) system, while the 108 M\odot, non-rotating satellite is modelled using 64,000 particles. The trajectories of the satellite particles are followed for several orbits of the satellite around the parent.
The generic features of a satellite that is being disrupted include: (1)~one or more breaks in the surface brightness profile, and (2)~associated twists and ellipticity changes in the isophote shape. These features closely resemble those seen in the M31 satellites M32 and NGC~205.
As a result of tidal interaction, the satellite's brightness profile tends to develop a deficiency (relative to the initial, intrinsic profile) over a particular range of radii --- a ``depletion'' zone --- exterior to which there is usually an upward break (``excess'' zone). The latter zone is populated by material that has become unbound from the satellite or that will soon become unbound.
Several trends are seen in the simulations --- as a function of orbital eccentricity, orbital phase, viewing geometry, and the steepness of the satellite's intrinsic density profile. For example, in highly eccentric orbits, the break in the brightness profile tends to occur at a radius that is significantly smaller than the theoretically estimated King tidal radius. Thus, the fact that M32's observed break radius is much smaller than the theoretical tidal radius suggests that its orbit is highly non-circular.
These simulations are currently being extended to cover a wider range of parameter space and to tailor them to the case of the M31/M32/NGC~205 system. They will also be compared to recent Keck spectroscopic measurements of the mean stellar velocity and dispersion around M32's break radius.