Dwarf satellite galaxies in the modified dynamics

In the modified Newtonian dynamics (MOND) the inner workings of dwarf satellites can be greatly affected by their mother galaxy-over and beyond tidal effects. Because of MOND's nonlinearity, a system's internal dynamics can be altered by an external field in which it is immersed (even when this field, by itself, is constant in space). As a result, the size and velocity dispersion of the satellite vary as the external field varies along its orbit. A notable outcome of this is a substantial increase in the dwarfs vulnerability to eventual tidal disruption-rather higher than Newtonian dynamics (with a dark matter halo) would lead us to expect for a satellite with given observed parameters. The space of system parameters of the dwarf may be divided according to three main criteria: It can be either external- or internal-held dominated; it can be in the adiabatic or in the impulsive regime; and it can be in the tidal or nontidal regime. The Milky Way's dwarf satellites populate all these regions of parameter space, and a single dwarf on an eccentric orbit can traverse several of them. The situation is particularly transparent in the external-held dominated, adiabatic regime where the dynamics can be described analytically: because of the variation in the external field strength with the galactocentric distance of the dwarf, R, its size changes as R-l, and the internal velocities change as R. As the dwarf approaches the center it puffs up, becoming susceptible to tidal disruption. Adiabaticity is lost roughly at the same R at which tidal effects become important. The behavior near and in the impulsive regime is studied numerically.