An H-alpha survey of the host environments of 77 type IIn supernovae within z<0.02

Abstract

Type IIn supernovae (SNe,IIn) are an uncommon and highly heterogeneous class of SN where the SN ejecta interact with pre-existing circumstellar media (CSM). Previous studies have found a mass ladder in terms of the association of the SN location with H$α$ emission and the progenitor masses of SN classes. In this paper, we present the largest environmental study of SNe,IIn. We analyse the H$α$ environments of 77 type IIn supernovae using continuum subtracted H$α$ images. We use the pixel statistics technique, normalised cumulative ranking (NCR), to associate SN pixels with H$α$ emission. We find that our 77 SNe,IIn do not follow the H$α$ emission. This is not consistent with the proposed progenitors of SNe,IIn, luminous blue variables (LBVs) as LBVs are high mass stars that undergo dramatic episodic mass loss. However, a subset of the NCR values follow the H$α$ emission, suggesting a population of high mass progenitors. This suggests there may be multiple progenitor paths with $\sim$60% having non-zero NCR values with a distribution consistent with high mass progenitors such as LBVs and $\sim$40% of these SNe not being associated with H$α$ emission. We discuss the possible progenitor routes of SNe,IIn, especially for the zero NCR value population. We also investigate the radial distribution of the SNe in their hosts in terms of H$α$ and $r'$-band flux.