Hα emission from gaseous structures above galactic discs

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 Hα{\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 Hα{\rm{H}}\alpha line at height of ∼0.6 \sim 0.6–1.6kpc1.6\hspace{0.33em}{\rm{kpc}} above the disc depending on cluster location and gas metallicity. The Hα{\rm{H}}\alpha surface brightness ranges within ∼10−17 \sim 1{0}^{-17}–10−16ergs−1cm−2arcsec−21{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 Hα{\rm{H}}\alpha emission of extraplanar structures can be explained by recombination in collisionally ionized gas of unstable shells driven by multiple SNe.

Keywords

• galaxies
• halos – starburst – ism – ism
• bubbles – shock waves – supernova remnants