Post-starburst (PSB) galaxies are defined as having experienced a recent
burst of star formation, followed by a prompt truncation in further activity.
Identifying the mechanism(s) causing a galaxy to experience a post-starburst
phase therefore provides integral insight into the causes of rapid quenching.
Galaxy mergers have long been proposed as a possible post-starburst trigger.
Effectively testing this hypothesis requires a large spectroscopic galaxy
survey to identify the rare PSBs as well as high quality imaging and robust
morphology metrics to identify mergers. We bring together these critical
elements by selecting PSBs from the overlap of the Sloan Digital Sky Survey and
the Canada-France Imaging Survey and applying a suite of classification
methods: non-parametric morphology metrics such as asymmetry and Gini-M20, a
convolutional neural network trained to identify post-merger galaxies, and
visual classification. This work is therefore the largest and most
comprehensive assessment of the merger fraction of PSBs to date. We find that
the merger fraction of PSBs ranges from 19% to 42% depending on the merger
identification method and details of the PSB sample selection. These merger
fractions represent an excess of 3-46x relative to non-PSB control samples. Our
results demonstrate that mergers play a significant role in generating PSBs,
but that other mechanisms are also required. However, applying our merger
identification metrics to known post-mergers in the IllustrisTNG simulation
shows that ~70% of recent post-mergers (<200 Myr) would not be detected. Thus,
we cannot exclude the possibility that nearly all post-starburst galaxies have
undergone a merger in their recent past.