Stellar-gas kinematic misalignments in galaxies: Longevity of misalignments and implications for galaxy evolution in the EAGLE simulation

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. These misalignments are predicted to be short-lived (lifetimes ~100 Myr), apart from in the presence of continued external accretion. However, such relaxation timescales are unable to explain the distribution of misalignments observed in 30-40% of early-type galaxies (ETGs). In this talk, I am going to present the results obtained by using the cosmological hydrodynamical simulation EAGLE 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 find good agreement with existing observational results from SAMI/MaNGA and mm-interferometers (such as ALMA), with 39±5% of ETGs showing significant misalignments at z=0. The misalignments coincide with mergers only ~16% of the time, with median relaxation timescales of ~300 Myr and only 6% of misalignments lasting longer than 1 Gyr. The use of EAGLE and future cosmological simulations allows us to constrain the physical processes extending the relaxation times, shedding light on the gas accretion processes that fuel star formation and AGN activity in massive galaxies.