Starburst-driven Mass Loss from Dwarf Galaxies: Efficiency and Metal Ejection

We model the effects of repeated supernova explosions from starbursts in dwarf galaxies on the interstellar medium of these galaxies, taking into account the gravitational potential of their dominant dark matter haloes. We explore supernova rates from one every 30,000 yr to one every 3 million yr, equivalent to steady mechanical luminosities of L = 0.1− 10× 10 ergs s, occurring in dwarf galaxies with gas masses Mg = 10 6 − 10M . We address in detail, both analytically and numerically, the following three questions: 1. When do the supernova ejecta 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 ≤Mg ≤ 10M . Surprisingly, we find that the mass ejection efficiency is very low for galaxies with mass Mg ≥ 10M . Only galaxies with Mg ∼< 10 M have their interstellar gas blown away, and then virtually independently of L. On the other hand, metals from the supernova ejecta are accelerated to velocities larger than the escape speed from the galaxy far more easily than the gas. We find that for L38 = 1, only about 30% of the metals are retained by a 10 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. Subject headings: Hydrodynamics – Shock waves – Galaxies: Dwarfs – Numerical Methods