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On the association between core-collapse supernovae and HII regions

Previous studies of the location of core-collapse supernovae (ccSNe) in their host galaxies have variously claimed an association with HII regions; no association; or an association only with hydrogen-deficient ccSNe. Here, we examine the immediate environments of 39 ccSNe whose positions are well known in nearby (<15 Mpc), low inclination (<65 degrees) hosts using mostly archival, continuum-subtracted H-alpha ground-based imaging. We find that 11 out of 29 hydrogen-rich ccSNe are spatially associated with HII regions (38 +/- 11%), versus 7 out of 10 hydrogen-poor ccSNe (70 +/- 26%). Similar results from Anderson et al. led to an interpretation that the progenitors of type Ib/c ccSNe are more massive than those of type II ccSNe. Here, we quantify the luminosities of HII region either coincident with, or nearby to the ccSNe. Characteristic nebulae are long-lived (~20 Myr) giant HII regions rather than short-lived (~4 Myr) isolated, compact HII regions. Therefore, the absence of a HII region from most type II ccSNe merely reflects the longer lifetime of stars with <12 Msun than giant HII regions. Conversely, the association of a HII region with most type Ib/c ccSNe is due to the shorter lifetime of stars with >12 Msun stars than the duty cycle of giant HII regions. Therefore, we conclude that the observed association between certain ccSNe and HII provides only weak constraints upon their progenitor masses. Nevertheless, we do favour lower mass progenitors for two type Ib/c ccSNe that lackassociated nebular emission, a host cluster or a nearby giant HII region. Finally, we also reconsider the association between long Gamma Ray Bursts and the peak continuum light from their (mostly) dwarf hosts, and conclude that this is suggestive of very high mass progenitors, in common with previous studies.