Tidal Tails around Globular Clusters: Are They a Good Tracer of Cluster Orbits?

Abstract

International audienceWe present the results of detailed N-body simulations of clusters moving in a realistic Milky Way (MW) potential. The strong interaction with the bulge and the disk of the Galaxy leads to the formation of tidal tails, emanating from opposite sides of the cluster. Some characteristic features in the morphology and orientation of these streams are recognized and interpreted. The tails have a complex morphology, particularly when the cluster approaches its apogalacticon, showing multiple ``arms'' in remarkable similarity to the structures observed around NGC 288 and Willman 1. Actually, the tails are generally good tracers of the cluster path quite far from the cluster center (>7-8 tidal radii), while on the smaller scale they are mainly pointing in the direction of the Galaxy center. In particular, the orientation of the inner part of the tails is highly correlated with the cluster orbital phase and the local orbital angular acceleration. This implies that, in general, the orbital path cannot be estimated directly from the orientation of the tails, unless a sufficient large field around the cluster is available