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Title: The environments and progenitors of extreme supernovae in the low-redshift universe
Author: Taggart, Kirsty
ISNI:       0000 0004 9359 2956
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2020
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Core-collapse supernovae (CCSNe) are the explosive endpoints of massive (>8 M_Sun) stars that manifest as a bright optical display that lasts for a period of weeks to several months, leaving behind a stellar-mass black hole or a neutron star corpse. Currently supernova science is in a phase of unprecedented activity and productivity, with a new generation of wide-field survey telescopes that scan the entire night sky every few days. As a result, we have begun to discover huge diversity in the observational and physical explosion properties of supernovae that do not neatly fit into the standard classification scheme derived nearly a century ago. Some supernovae produce relativistic jets and are accompanied by long-duration gamma-ray bursts (LGRBs), and superluminous supernovae (SLSNe) have radiated luminosities that exceed CCSNe by an order of magnitude, suggesting an energetic and poorly understood explosion mechanism. In this thesis, I take advantage of new unbiased supernova samples to provide insights into the explosive endpoints of massive stars through their host galaxy environments. I use public imaging surveys to gather multi-wavelength photometry for a spectroscopically-complete sample of 150 CCSN host galaxies from the All-Sky Automated Survey for Supernovae (ASAS-SN) and fit the resulting spectral energy distributions (SEDs) to derive stellar masses and integrated star formation rates. I find that 33(+ 4)(- 4) per cent of CCSNe take place in dwarf galaxies (stellar mass, M < 10^9 M_Sun) and 2(+ 2)(- 1) per cent in dwarf starburst galaxies (specific star formation rate, sSFR > 10^(-8) yr^(-1)). CCSNe provide a census of all massive star formation. Thus, this new CCSN catalogue is an ideal `control' sample to compare with exotic supernovae (SLSNe and LGRBs) at low redshift. I reanalyse SLSN and LGRB hosts from the literature (out to z< 0.3) in a homogeneous way to compare against the CCSN host sample. I conclude that the relative SLSN-I to CCSN supernova rate is increased in low-mass galaxies and at high specific star formation rates. These parameters are strongly covariant, and it was not possible to securely identify which factor (low mass or high sSFR) was more strongly associated with an enhanced SLSN or LGRB rate. In addition, I present my work to help to build future supernova catalogues with the Zwicky Transient Facility (ZTF), including the Bright Transient and Superluminous Supernova surveys. I have integrated the Liverpool Telescope with ZTF which allows follow-up spectroscopy and photometry to be requested and reduced via an automated reduction and image-subtraction pipeline. These new transient catalogues will be larger, and they will provide better control of systematics, enabling detailed future studies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: QB Astronomy ; QC Physics