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 ; they also regulate the pressure of the ISM and consequently 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 \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 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 } .
Specific comparisons with well studied dI galaxies , as for example Leo A , yield excellent agreement with the data .
Based on our results , we discuss a scenario in which late type and early type dwarfs had common progenitors in the past , but differences in their total mass forced these objects to follow different evolutionary paths .
Therefore , we consider dI \rightarrow dE transitions occurring at present cosmic times as very unlikely .