Exploring the merger-starburst connection
The hierarchical nature of the currently favoured model of ΛCDM cosmology points to mergers as a natural channel through which structures in the Universe form and evolve.
Theoretical models of gas-rich major galaxy mergers show that they can transform disks into highly-concentrated spheroids, and induce centralised starbursts strong enough to consume a significant amount of the galaxies’ gas reservoir. Consequently, these dynamically disruptive events are considered a plausible mechanism responsible for star-formation quenching and, what follows, the transition of galaxies between the blue cloud and the red sequence.
Evidence of mergers of galaxies have been found in observations both in the Local Universe and at higher redshifts, however their frequency of occurrence is difficult to constrain due to the varying sample selection criteria with the stage of the merger, as well as the dependance of the prominence and timescales of the merger signatures on the conditions and geometry of the interaction.
I will introduce the `shape asymmetry’ (Pawlik et al. 2016), a morphological indicator which represents a robust method for automated selection of galaxies in the post-coalescence merger stages, which we have combined with preexisting measures of galaxy structure to study the role of galaxy mergers in triggering bursty star formation. Our analysis of an evolutionary sample of (post-)starburst galaxies (Wild et al. 2010) revealed that ~50% of the galaxies with the youngest starbursts (less than 0.1Gyr) show presence of asymmetric features in their outskirts, indicating a recent merger, and that this fraction declines with the starburst age over the next 0.5 Gyr - a trend resembling that expected for post-mergers with fading tidal features. I will also present results of our more recent work, where we investigate how the role of mergers in inducing spectroscopic starburst signatures varies with the stellar mass of the galaxies, and I
will compare the timescale of the morphological disturbance observed in (post-)starburst galaxies with that found in hydrodynamic simulations of galaxy mergers.