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

Abstract

We model the effects of repeated supernova explosions from starbursts in\ndwarf galaxies on the interstellar medium of these galaxies, taking into\naccount the gravitational potential of their dominant dark matter haloes. We\nexplore supernova rates from one every 30,000 yr to one every 3 million yr,\nequivalent to steady mechanical luminosities of L=0.1-10 x 10^38 ergs/s,\noccurring in dwarf galaxies with gas masses M_g=10^6 - 10^9 solar masses. We\naddress in detail, both analytically and numerically, the following three\nquestions:\n 1. When do the supernova ejecta blow out of the disk of the galaxy?\n 2. When blowout occurs, what fraction of the interstellar gas is blown away,\nescaping the potential of the galactic halo?\n 3. What happens to the metals ejected from the massive stars of the\nstarburst? Are they retained or blown away?\n We give quantitative results for when blowout will or will not occur in\ngalaxies with 10^6 \\leq M_g \\leq 10^9 solar masses. Surprisingly, we find that\nthe mass ejection efficiency is very low for galaxies with mass M_g \\geq 10^7\nsolar masses. Only galaxies with M_g \\leq 10^6 solar masses have their\ninterstellar gas blown away, and then virtually independently of L. On the\nother hand, metals from the supernova ejecta are accelerated to velocities\nlarger than the escape speed from the galaxy far more easily than the gas. We\nfind that for L_38=1, only about 30% of the metals are retained by a 10^9 solar\nmass galaxy, and virtually none by smaller galaxies. We discuss the\nimplications of our results for the evolution, metallicity and observational\nproperties of dwarf galaxies.\n