ON THE TIDAL DISRUPTION OF DWARF SPHEROIDAL GALAXIES AROUND THE GALAXY

The Milky Way induces a strong tidal perturbation on its satellite dwa rf spheroidal galaxies. We present numerical simulations of tidal inte ractions between these low-density dwarf spheroidal galaxies and the M ilky Way. Our results indicate that dwarf spheroidal galaxies with lim iting radius much larger than the theoretical tidal radius are unstabl e and likely to be tidally disrupted on a Hubble time. However, dwarf spheroidal galaxies can survive over a Hubble time if their limiting r adii are less than twice their tidal radii at perigalacticon. In a gal axy which is undergoing tidal disruption, (1) the projected surface de nsity is flattened in the galaxy's orbital plane and follows a power-l aw distribution from the galaxy's center, (2) the velocity dispersion is sustained at the current virial equilibrium value, and (3) the cent ral density of the residual remnant is maintained even after most of t he initial mass is lost. Beyond the tidal radius, the escapers have a radial velocity gradient along the azimuthal direction of the galaxy's motion. When compared with observational data, our theoretical result s are consistent with the scenarios that (1) some dwarf spheroidal gal axies contain dark matter, and (2) some dwarf spheroidal galaxies may be part of the debris that was tidally torn from the LMC by the Galaxy .