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

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Abstract

We model the effects of repeated supernova explosions from starbursts in the centers of dwarf galaxies on the interstellar medium of these galaxies, taking into account the gravitational potential of a dominant dark matter halo. 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 x 10^38 ergs/s, occurring in dwarf galaxies with gas masses M_g = 10^6-10^9 Msun. We address in detail, both analytically and numerically, the following three questions: 1. When do the supernova ejecta blow out of the galaxy, and when is the entire interstellar medium blown away? 2. What fraction of gas escapes the galaxy if blowout occurs? 3. What happens to the metals ejected from the massive stars of the starburst? We give quantitative results for when blowout will or will not occur in galaxies with 10^6 < M_g < 10^9 Msun. Surprisingly, we find that the mass ejection efficiency is very low in such outflows for galaxies with mass M_g > 10^7 Msun. Only galaxies with M_g < 10^6 Msun 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 L_38=1, about 97% of the metals are retained by a 10^9 Msun galaxy, but this fraction is already only 40% for M_g=10^8 Msun and decreases to 0.27% for M_g=10^7 Msun. We discuss the implications of our results for the evolution, metallicity and observational properties of dwarf galaxies.

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