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 ≃109M⊙ 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 ϕ≈0−30 with
about 65% of the dwarfs in the sample having ϕ≈0−10; (iii) we
predict a lower limit to the oxygen abundance in dIs of 12+log(O/H)≈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 ×108M⊙ 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
Z3.5. (Abridged)Comment: 56 pages, aasms4.sty, LaTeX, 12 figures. MNRAS, submitte