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

TL;DR

This study evaluates whether impacts from Galactic Globular Clusters significantly contribute to the heating of the Galactic disk, concluding they have a minor role compared to other mechanisms like molecular clouds and spiral arms.

Contribution

It introduces an analysis of Globular Cluster impacts as a potential disk heating mechanism, finding their contribution to be minimal compared to other known processes.

Findings

Globular Clusters could heat the disk to σ_z = 5.5 km/s, below observed values.

The rate of disk heating from Globular Clusters is similar to that from molecular cloud scattering.

Globular Clusters contribute only a small fraction to the total disk energy.

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 {$\sigma $}$_{z}$ = 5.5kms$^{{\rm -} {\rm 1}}$ (c.f. the observed 18 and 39 kms$^{{\rm -} {\rm 1}}$ for the thick and thin disks respectively). We find that the rate of rise of disk heat ($\alpha$=0.22 in \textit{$\sigma $}$_{z}$ $\sim t^{\alpha}$ with \textit t being time), is close to that found for scattering by molecular clouds.