Detecting the effect of Globular Cluster impacts on the disk of the Milky Way

Abstract

The crossing of the Galactic disk by a Globular Cluster could produce star formation due to gravitational focussing or compression of disk material. We report on simulations of the effect on disk material which reveal that the crossing can sometimes cause local gravitational focussing of disk material. We also present the salient points of a little-known paper by Levy (2000), that shows that strong compression can result from the shock wave generated by GC disk crossing. The main thrust of our paper is a search for remnants of disk crossings by Globular Clusters. Using the gravitational potential of the Galaxy to locate the position of the most recent crossings of a subset of fifty-four Globular Clusters reveals that systematic errors and uncertainties in initial conditions limit the scope for unequivocal identification. From the subset of fifty-four, six possible search sites with the best constraints are retained for further scrutiny. Three of the six potentially promising search areas in the disk are from Globular Clusters NGC 3201, 6397 and NGC 6838, for which we cannot rule out some observed star associations observed nearby as being remnants. The three other of the six areas are too large to provide meaningful identification of remnants. Also, a possible remnant (open cluster NGC6231) is shown not to be due to Globular Cluster impact, contrary to a previous report. In a more wide-ranging screening of one hundred and fifty-five Globular Clusters we identify which Globular Clusters are compatible with being responsible for the formation of any of the Galaxy's five most prominent Star Super Clusters.