High resolution H i observations of nearby dwarf galaxies ( most of which are situated in the M 81 group at a distance of about 3.2 Mpc ) reveal that their neutral interstellar medium ( ISM ) is dominated by hole–like features most of which are expanding .
A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies ( such as M 31 and M 33 ) shows that they tend to reach much larger sizes in dwarf galaxies .
This can be understood in terms of the galaxy ’ s gravitational potential .
The origin of these features is still a matter of debate .
In general , young star forming regions ( OB–associations ) are held responsible for their formation .
This picture , however , is not without its critics and other mechanism such as the infall of high velocity clouds , turbulent motions or even gamma ray bursters have been recently proposed .
Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures .
This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova–explosions which shape the neutral interstellar medium of ( dwarf ) galaxies .