H alpha emission from gaseous structures above galactic discs

Extraplanar structures of ionized gas are detected in numerous edge-on galaxies. Whether HII regions or supernovae (SNe) responsible for its ionization is still debated. Here, we consider the H alpha emissivity from shells of superbubbles driven by SNe explosions in a stellar cluster located either in the midplane or above the midplane of the disc. We found that these shells form filamentary structures emitting brightly in H alpha line at height of similar to 0.6-1.6 kpc above the disc depending on cluster location and gas metallicity. The Ha surface brightness ranges within similar to 10(17)-10(16) erg s(-1) cm(-2) arcsec(-2) are close to the values observed in edge-on galaxies. We conclude that the Ha emission of extraplanar structures can be explained by recombination in collisionally ionized gas of unstable shells driven by multiple SNe.