University of Kiel
|Accepted by||Monthly Notices of the Royal Astronomical Society|
The velocity-dispersion of solar-neighbourhood stars increases more rapidly with stellar age than theoretical calculations of orbital diffusion predict. Interpreting this difference to arise from star formation characterised by larger cluster masses, rather than as yet unknown stellar-dynamical heating mechanisms, suggests that the star formation rate in the MW disk has been quietening down, or at least shifting towards less-massive star-forming units. Thin-disk stars with ages 3-7 Gyr may have formed from an ICMF extending to very rich Galactic clusters. Stars appear to be forming preferentially in modest embedded clusters during the past 3 Gyr.
Applying this approach to the ancient thick disk of the Milky Way, it follows that its large velocity dispersion may have been produced through a high star formation rate and thus an ICMF extending to massive embedded clusters (~105-6 MO), even under the extreme assumption that early star formation occurred in a thin gas-rich disk. This enhanced star-formation episode in an early thin Galactic disk could have been triggered by passing satellite galaxies, but direct satellite infall into the disk may not be required for disk heating.