Could the Galactic disk heating be due to Globular Cluster impacts?

Abstract

So far, six mechanisms have been proposed to account for the Galactic disk heating. Of these, the most important appear to be a combination of scattering of stars by molecular clouds and by spiral arms. We study a further mechanism, namely, the repeated disk impact of the original Galactic Globular Cluster population up to the present. We find that Globular Clusters could have contributed at most a small fraction of the current vertical energy of the disk, as they could heat the whole disk to {$\ddot{I}ƒ$}${}_z$ = 5.5kms${}^{-1}$ (c.f. the observed 18 and 39 kms${}^{-1}$ for the thick and thin disks respectively). We find that the rate of rise of disk heat ($\hat{I}\pm$=0.22 in \textit{$\ddot{I}ƒ$}${}_z$ $\sim t^{\hat{I}}\pm$ with \textit t being time), is close to that found for scattering by molecular clouds.

4 pages, 1 figure, accepted for publication in MNRAS on 2009/May/14