Impacts of Radial Migration and Flaring on the Galactic Thick and Thin Disks
Daisuke Kawata (Mullard Space Science Laboratory, University College London)
We first summarise the thick and thin disk formation scenario commonly seen in cosmological N-body simulations. As suggested in Brook et al. (2004), a hierarchical clustering scenario causes multiple minor gas-rich mergers, and leads to the formation of kinematically hot, higher [alpha/Fe] thick disk population, at a high redshift. Once the mergers become less significant at later epoch, the lower [alpha/Fe] thin disk population starts building up. In addition, we show that the current cosmological simulation also naturally predict that the thin disk population is flaring at the outer region. Consequently, at the high vertical height from the disk plane, the compact thick disk population is dominant in the inner region and the flaring thin disk population contributes more in the outer region. This helps to explain the positive radial metallicity gradient and negative radial [alpha/Fe] gradient observed at the high vertical height in the Milky Way stellar disk. We then discuss how radial migration impacts the metallicity distribution of the thin disc population. We demonstrate that the flaring star forming region could be required to explain the negative vertical metallicity gradient observed in the thin disc population.