ИСТИНА

The neutral gas distribution in the large number of nearby galaxies appears as complexes of shells and supershells with a size up to 1-2 kpc (so-called supergiant shells, SGS). According to modern understanding these structures were created by stellar winds and supernova explosions from multiple star formation events over the lifetime of the SGS. The SGSs expansion may trigger the new bursts of star formation in their rims. As the result, the ionized gas structure in such galaxies appears as HII complexes located mostly in the walls of the giant HI supershells. The Hα emission also observed inside the small HI shells, but never before giant ionized shells were observed inside the HI SGSs. We performed the observations with scanning Fabry-Perot interferometer as well as with narrow-band filters at 6-m telescope of SAO RAS and for the first time detected the presence of the ionized kpc-sized supershells in Hα line inside the HI SGSs in IC 2574 and Holmberg II galaxies. Here we present the results of observations and discuss the possible nature of these structures.