Published online by Cambridge University Press: 25 April 2016
The supernova rate in spirals of types Sc and Sd shows a sharp peak in face-on galaxies with inclination i ≤ 25°. This suggests that most supernovae in late-type galaxies occur in rich clusters or associations that are located at the base of chimney-like structures formed by a previous generation of supernovae. These chimneys are transparent because most of the dust contained in the rising column of gas within them had previously been destroyed in the hot bubble surrounding supernovae.