Young Sun Lee (New Mexico State University)

Observational Constraints on the Formation of the Milky Way's Thick Disk

The Milky Way's thick disk has different observational properties in terms of its structure, kinematics, and chemical abundances from the thin disk. These discrepancies indicate that the thick disk has experienced different formation and/or evolution history from its counterpart. The currently discussed mechanisms for the thick-disk formation are dynamical heating of pre-existing thin disk by satellite mergers, accretion of satellite galaxies, chaotic mergers of gas-rich systems, and radial migration of stars. In this talk, on the basis of [alpha/Fe] ratios measured for a large sample of G-type dwarf stars from the Sloan Extension for Galactic Understanding and Exploration (SEGUE), I divide the sample into likely thin- and thick-disk populations, and explore the observed correlations of rotational velocity with metallicity, Galactocentric distance and distance from the Galactic plane, as well as the distribution of orbital eccentricities for the individual populations. These observed properties are also compared with predictions from the formation scenarios mentioned above in order to provide observational constraints.