Type Ibc supernovae in disturbed galaxies: evidence for a top-heavy IMF
  We compare the radial locations of 178 core-collapse supernovae to the R-band
and H alpha light distributions of their host galaxies. When the galaxies are
split into `disturbed' and `undisturbed' categories, a striking difference
emerges. The disturbed galaxies have a central excess of core-collapse
supernovae, and this excess is almost completely dominated by supernovae of
types Ib, Ic and Ib/c, whereas type II supernovae dominate in all other
environments. The difference cannot easily be explained by metallicity or
extinction effects, and thus we propose that this is direct evidence for a
stellar initial mass function that is strongly weighted towards high mass
stars, specifically in the central regions of disturbed galaxies.
