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

Mordecai-Mark Mac Low Max-Planck-Institut für Astronomie
Andrea Ferrara Osservatorio Astrofisico di Arcetri

The Astrophysical Journal, 513, in press, 1 March 1999

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 x 1038 erg s-1, occurring in dwarf galaxies with gas masses Mg = 106 - 109 solar masses. 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 Mg up to 109 solar masses. Surprisingly, we find that the mass ejection efficiency is very low in outflows for galaxies with mass Mg > 107 solar masses. Only galaxies with Mg < 106 solar masses 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 109 solar mass galaxy, and virtually none by smaller galaxies. We discuss the implications of our results for the evolution, metallicity and observational properties of dwarf galaxies.
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