Speaker
Description
Mergers and accretion events are a key element of the baryon cycle, and have strong impacts on the distribution, kinematics and mixing of gas in galaxies. Major mergers are well studied in this regard, but gas-rich minor mergers and cold gas accretion are much less well constrained. A key probe of these external gas accretion events are kinematic misalignments between the stellar and the cold gas components. In the absence of continued smooth accretion, misalignments are predicted to be short-lived (lifetimes ~100 Myr). However, such short relaxation timescales are unable to explain the distribution of misalignments observed in ~40% of early-type galaxies (ETGs).
In this talk, I am going to present the results obtained by using the EAGLE cosmological simulation to investigate the stellar-gas misalignment relaxation timescales over a large, representative galaxy population (approx. 5,600 galaxies) from present day to z=1. We show for the first time that misalignments have relatively short median relaxation timescales of ~500 Myr, with ~20% of misalignments persisting on timescales significantly longer than predicted. Additionally, misalignment formation coincides with mergers in only ~17% of cases. Our results point toward cold gas replenishment in massive galaxies occuring through diverse pathways, with halo cooling and accretion playing an important role in maintaining misalignments in massive galaxies. The use of EAGLE and future cosmological simulations allows us to constrain the internal and external processes through which galaxies can replenish their cold gas that fuel star formation and AGN activity in massive galaxies.
