Unveiling the evolutionary history of local post-starburst galaxies through careful Bayesian modelling of their spectra

Abstract

When we gaze upon the night sky into the stars in the Milky Way, it seems that the cosmos is constant, at least in the timescale of a lifetime. However, as our telescopes continued to improve, we have discovered that galaxies are instead dynamic systems, evolving across millions to billions of years. One of the most important evolution is quenching, the shutting down of star formation and transitioning into quiescence. Aiming to understand what physical mechanisms lead to these dramatic changes, and how they affect star formation, this thesis focuses on a special type of galaxy in transition.

Post-starburst galaxies are galaxies that have recently undergone a period of starburst, quickly followed by rapid quenching. Their unique recent history makes them excellent laboratories to study the effects of rapid quenching on the galaxies' stellar, gas, dust, morphological and dynamical properties. To accurately extract the stellar properties of post-starburst galaxies from the "fossil records" embedded in their observed spectra, I improved on existing Bayesian spectral fitting techniques, which results in more accurate and precise measurements of galaxy properties.

Using the improved method, I fit the observed spectra of the post-starburst regions in ~90 local post-starburst galaxies, and demonstrated that most post-starburst regions, regardless of their spatial location, significant increase in stellar metallicity during the recent starburst. This finding could imply that a significant portion of the present-day red sequence have been assembled through a rapid quenching phase.

Through developing a novel hierarchical Bayesian fitting approach to fit data from integral field spectroscopic surveys, I extracted the spatially resolved star-formation histories, metallicity histories and dust properties of three post-starburst galaxies in the previous sample. The results showed that these galaxies experienced an outside-in sequence of starburst and quenching, which is consistent with the effects of gas-rich galaxy mergers in simulations.

Date of Award	30 Jun 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Vivienne Wild (Supervisor) & Michail Papathomas (Supervisor)