The Role of Stellar Feedback and Dark Matter in the Evolution of Dwarf Galaxies

Abstract

Supernova and multiple supernova events regulate several structural properties of dwarf galaxies. In particular, they govern the metal enrichment and the energy budget of the ISM; they might induce partial (blowout) or total (blowaway) gas removal from the galaxy; the morphology of the galactic gaseous body. Significant amounts of dark matter may play an equally important role: the dark matter gravitational potential tends to concentrate baryons towards the center, thus enhancing both the star formation rate and metal production. Also, the dynamical properties of the ISM, and the occurrence of a blowout or blowaway are shown to be determined by the dark matter content. We present detailed analytical/numerical models describing the evolution of dwarf Irregular galaxies including the above and other effects. The main results are: (i) dwarfs with total masses $M\simlt 5\times 10^6 M_\odot$ are blown away; those with gas masses up to $\simeq 10^9 M_\odot$ lose mass in an outflow; (ii) metallicities are found to correlate tightly with dark matter content and are consistent with a range of dark-to-visible mass ratios $\phi\approx 0-30$ with about 65% of the dwarfs in the sample having $\phi\approx 0-10$; (iii) we predict a lower limit to the oxygen abundance in dIs of $12+log(O/H)\approx 7.2$; (iv) outflows are not particularly important for the metallicity evolution of dwarf galaxies and certainly less than star formation for gas consumption; however, dwarfs with gas masses few $\times 10^8 M_\odot$ are shown to be the major pollutants of the IGM; (v) the ISM HI velocity dispersion correlates with metallicity and, indepentently of dark matter, scales as $Z^{3.5}$. (Abridged)