Signatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)

TL;DR

This study combines photometric observations and N-body simulations to identify and analyze tidal features around the globular cluster NGC 6981, revealing ongoing mass loss due to tidal disruption and extended stellar tails.

Contribution

It provides new observational evidence of tidal tails in NGC 6981 and uses simulations to interpret the spatial distribution of tidal debris, enhancing understanding of cluster disruption processes.

Findings

Detection of extra-tidal features and stellar tails extending from NGC 6981.

Identification of long leading and trailing tails aligned with the cluster's velocity.

Evidence that the cluster lost most of its mass during perigalactic passages.

Abstract

We study the outer regions of the Milky Way globular cluster NGC6981 from publicly available $BV$ photometry and new Dark Energy Camera (DECam) observations, both reaching nearly 4 mag below the cluster main sequence (MS) turnoff. While the $BV$ data sets reveal the present of extra-tidal features around the cluster, the much larger field of view of DECam observations allowed us to identify some other tidal features, which extend from the cluster toward the opposite direction to the Milky Way center. These cluster structural features arise from stellar density maps built using MS stars, once the cluster color-magnitude diagram was cleaned from the contamination of field stars. We also performed $N$-body simulations in order to help us to understand the spatial distribution of the extra-tidal debris. The outcomes reveal the presenceof long trailing and leading tails mostly parallel to the direction of the cluster velocity vector. We found that the cluster has lost most of its mass by tidal disruption during its perigalactic passages, that lasted nearly 20 Myr each. Hence, a decrease in the density of escaping stars near the cluster is expected from our $N$-body simulations, which in turn means that stronger extra-tidal features could be found out by exploring much larger areas around NGC6891.