| Results are presented for a series of numerical models of gas dynamical stripping of spherical galaxies moving through a uniform intergalactic medium. The models include replenishment of the interstellar medium by stellar deaths, removal of cold dense gas by a nominal "star formation" process, and radiative cooling by both thermal bremsstrahlung and collisionally-excited line emission. The effective distributions for the gas replenishment are chosen to mimic cases in which the replenished gas is mildly "stirred" by galactic fountains; this generates a broader distribution of gas than indicated by the distribution of luminous material in galaxies, but the injection of energy by supernovae is not sufficient to drive an actual galactic wind. The galaxy starts out with no interstellar gas; replenishment of the interstellar medium by star deaths begins at t = 0. Because sinks for the gas production are provided in addition to sources, the flow can evolve to a true steady state, unlike previous models without cooling flows or "star formation".;The degree of stripping is found to depend on the model param- eters as a function of (TURN)n(,icm)v(,gal)('2.4)/(')M(,rep) where n(,icm) is the intergalactic medium density, v(,gal) is the galaxy velocity, and (')M(,rep) is the rate at which the galaxy is replenishing its interstellar medium. Approximate empirical fitting formulae are provided for the steady state fraction of replenished gas which is retained by the galaxy, the amount of gas within the galaxy in excess of the ambient intergalactic medium, and the drag coefficient. Where possible, the formulae are related to a qualitative model in which gas with surface density for replenishment below a critical value is assumed to be stripped away.;The calculations were performed using a new two dimensional numerical gas dynamics computer code which combines an accurate second-order scheme (MacCormack method) with a monotone first-order scheme (upwind/donor-cell method) in such a way as to retain the second-order accuracy over most of the flow and only reducing to first-order accuracy as needed to retain stability.;The stripping of gas from galaxies is found to proceed by a combination of the following mechanisms: (1) sufficient momentum is transferred from the intergalactic gas to accelerate the interstellar gas to escape velocity; (2) sufficient kinetic energy is converted into heat to unbind the interstellar gas; (3) gas is stripped off by a rarefaction wave in the wake. |
