Hα emission from gaseous structures above galactic discs

Abstract

Abstract 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 α {\rm{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 α {\rm{H}}\alpha line at height of ∼ 0.6 \sim 0.6 – 1.6 kpc 1.6\hspace{0.33em}{\rm{kpc}} above the disc depending on cluster location and gas metallicity. The H α {\rm{H}}\alpha surface brightness ranges within ∼ 1 0 − 17 \sim 1{0}^{-17} – 1 0 − 16 erg s − 1 cm − 2 arcsec − 2 1{0}^{-16}\hspace{0.33em}{\rm{erg}}\hspace{0.33em}{{\rm{s}}}^{-1}\hspace{0.33em}{{\rm{cm}}}^{-2}\hspace{0.33em}{{\rm{arcsec}}}^{-2} are close to the values observed in edge-on galaxies. We conclude that the H α {\rm{H}}\alpha emission of extraplanar structures can be explained by recombination in collisionally ionized gas of unstable shells driven by multiple SNe.