On star formation in edge-on galaxies

Extraplanar diffuse ionized gas in edge-on spiral galaxies is thought to be an indicator of star formation activity in the parent galaxy. We argue that the z-extension and morphology of the diffuse ionized gas is expected to vary for different galaxies even with equal star formation rate per unit area, if they have different densities in the gas discs, different gravitational accelerations, and their OB associations have different luminosity distributions, We slow that the thickness of the gaseous halo is not a monotonic function of galactic luminosity: at high luminosities stellar activity supports a thick disc rather than an extended halo. The observed correlation between the extension of the extraplanar gas and the FIR luminosity of the underlying discs in edge-on galaxies can be explained either if the mechanical luminosity of SNe explosions is restricted from above by the values 0.3–0.5 × 10−4 erg cm−2 s−1, or if the star formation activity in the underlying galaxies is distributed non-homogeneously through out their discs.