Using supernovae as tracers of stellar populations

• Main Author: Habergham, Stacey Marie
• Published: Liverpool John Moores University 2013
• Subjects: 523.01
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590095

Despite years of intense research on the exact nature of core-collapse supernovae (CCSNe). much uncertainty still surrounds the progenitor systems of these explosions. Only the most common subtype (SNIIP) has a known origin. thanks (0 numerous direct observations of the progenitor stars. This thesis aims to constrain the progenitors of all subtypes of CCSNe by looking at the environments in which they explode, and to use the statistical distributions of the different' core-collapse subtypes to probe the star formation properties of interacting galaxies. I will present an analysis of the distributions of a large sample of CCSNe (278) in isolated and interacting host galaxies. paying close attention to the selection effects involved in conducting host galaxy supernova studies. When taking into account all of the selection effects within the host galaxy sample, the following conclusions are drawn: Within interacting, or 'disturbed', systems there is a real. and statistically significant. increase in the fraction or stripped-envelope supernovae (SE-SNe) in the central regions. Selection effects are shown not to drive this result, and so it is proposed that this study provides direct evidence for a high-mass weighted initial mass function within the central regions of disturbed galaxies. o Within 'undisturbed' spiral galaxies the radial distribution of type Ib and type Ic supernovae is statistically very different, with the latter showing a more centrally concentrated distribution. This could be driven by metallcity gradients in these undisturbed galaxies, or radial variations in other properties (binarity or stellar rotation) driving envelope loss in progenitor stars. This result is not found in 'disturbed' systems. where the distributions of type Ib and Ie supernovae are consistent. o There is an absence of SNIIn in the central regions of host galaxies, specifically there is a lack of faint SNIIn within 50 per cent of the host galaxy light. Whilst assumptions may indicate that this is an extinction effect, there is also a lack of bright SNIIn events in the outer 50 per cent of host galaxy light. This radial correlation with absolute magnitude may indicate an inherent population dependence on host galaxy environment. o The distributions of SNIIn and SNIe are found to be statistically very unlikely (0.1 per cent) to be drawn from the same parent population within this supernova sample. Literature suggests that the progenitors of both of these populations are very massive stars ( 50 M0 ), if this is truly the case then the very different distributions of each subtype becomes difficult to reconcile.