23) Origin of thick disks from high resolution simulations

Abstract: We present the first result on the formation and evolution of the thin and thick discs of spiral galaxies from the New Horizon (and Galactica) simulation. The cosmological hydrodynamic simulation, run with the AMR code RAMSES, contains ~150 galaxies of M_star > 10^9 Msun in its field environment of the sphere of 20 Mpc diameter. It uses up-to-date subgrid physical prescriptions including stellar and AGN feedback. The resolution is >40 pc spatial and 10^4 Msun stellar mass. The superb resolution resolves the vertical scale heights of disc galaxies, which allows us to monitor the formation and evolution of galactic discs. A few highlights from the simulation are as follows. The galactic discs form at z=3-1 in massive (>10^10 Msun) galaxies but much later in less massive galaxies. It takes a long time for a galaxy to develop a stable and massive disc because in the earlier time galaxy mergers were too frequent and the star formation rate was too high. After a stable disc settles, with time, the stars formed on the disc are dynamically heated while the disc defined and occupied by the youngest stars gets thinner. The vertical light profile is well described by two components with different scale heights which can be interpreted as thin and thick discs. The properties of thin and thick discs are consistent with observations. The thick disc component is dynamically hotter, older in age, poorer in metals compared to the thin disc component. Yet, there are no distinct formation channels that separate the thin and thick discs. They appear to be a result of a continuous in-situ star formation history with a minor contribution from accretion. We also quantify the contribution from different channels (in-situ star formation vs. accretion) for the thin and thick discs and the spheroidal component.

Bio: Sukyoung Yi is a Prof. at Yonsei University. Looking for a postdoc (galaxy form/evol, theory or obs)