Progenitor mass constraints for core-collapse supernovae from
  correlations with host galaxy star formation
  Using H-alpha emission as a tracer of on-going (<16 Myr old) and near-UV
emission as a tracer of recent (16-100 Myr old) star formation (SF), we present
constraints on core-collapse (CC) supernova (SN) progenitors through their
association with SF regions. We present statistics of a large sample of SNe;
163.5 type II (58 IIP, 13 IIL, 13.5 IIb, 19 IIn and 12 'impostors') and 96.5
type Ib/c (39.5 Ib and 52 Ic). Using pixel statistics our main findings and
conclusions are: 1) An increasing progenitor mass sequence is observed, implied
from an increasing association of SNe to host galaxy H-alpha emission. This
commences with the type Ia (SNIa) showing the weakest association, followed by
the SNII, then the SNIb, with the SNIc showing the strongest correlation to SF
regions. Thus our progenitor mass sequence runs Ia-II-Ib-Ic. 2) Overall SNIbc
are found to occur nearer to bright HII regions than SNII. This implies that
the former have shorter stellar lifetimes thus arising from more massive
progenitor stars. 3) While SNIIP do not closely follow the on-going SF, they
accurately trace the recent formation. This implies that their progenitors
arise from stars at the low end of the CC SN mass sequence, consistent with
direct detections of progenitors in pre-explosion imaging. 4) Similarly SNIIn
trace recent but not the on-going SF. This implies that, contrary to the
general consensus, the majority of these SNe do not arise from the most massive
stars. Results and constraints are also presented for the less numerous SNIIL,
IIb, and 'impostors'. Finally we present analysis of possible biases in the
data, the results of which argue strongly against any selection effects that
could explain the relative excess of SNIbc within bright HII regions. Thus
intrinsic progenitor differences in the sense of the mass sequence we propose
remain the most plausible explanation of our findings.
