Starburst-driven mass loss from dwarf galaxies: Efficiency and metal ejection

We model the effects of repeated supernova (SN) explosions from starbursts in dwarf galaxies on the interstellar medium of these galaxies, taking into account the gravitational potential of their dominant dark matter halos. We explore SN rates from one every 30,000 yr to one every 3 Myr, equivalent to steady mechanical luminosities of L = 0.1-10 x 10(38) ergs s(-1), occurring in dwarf galaxies with gas masses M-g = 10(6)-10(9) M.. We address in detail, both analytically and numerically, the following three questions : 1. When do the SN ejects blow out of the disk of the galaxy? 2. When blowout occurs, what fraction of the interstellar gas is blown away, escaping the potential of the galactic halo? 3. What happens to the metals ejected from the massive stars of the starburst? Are they retained or blown away? We give quantitative results for when blowout will or will not occur in galaxies with 10(6) less than or equal to M-g less than or equal to 10(9) M.. Surprisingly, we find that the mass ejection efficiency is very low for galaxies with mass M-g greater than or equal to 10(7) M.. Only galaxies with M-g less than or similar to 10(6) M. have their interstellar gas blown away, and then virtually independently of L. On the other hand, metals from the SN ejecta are accelerated to velocities larger than the escape speed from the galaxy far more easily than the gas. We find that for L-38 = 1, only about 30% of the metals are retained by a 10(9) M. galaxy, and virtually none by smaller galaxies. We discuss the implications of our results for the evolution, metallicity, and observational properties of dwarf galaxies.