Detection of a 50 degree-long Trailing Tidal Tail for the Globular Cluster M5

TL;DR

Using Gaia DR2 data, we identify a 50-degree-long trailing tidal tail of the globular cluster M5, revealing episodic tidal stripping and providing candidate stars for future spectroscopic studies.

Contribution

This study is the first to detect and characterize a long trailing tidal tail of M5 using Gaia data, highlighting episodic stripping and offering candidate stars for follow-up.

Findings

Detected a 50-degree-long tidal tail of M5

Identified about 70 candidate stream stars

Evidence of episodic tidal stripping

Abstract

Using photometry and proper motions from Gaia Data Release 2, we detect a 50 degree-long stream of about 70 stars extending westward from the halo globular cluster M5. Based on the similarities in distance, proper motions, inferred color-magnitude distribution, and trajectory, we identify this stream as the trailing tidal tail of M5. While the surface density of stars is very low (~1.5 stars per square degree, or approximately 35 magnitudes per square arcsecond), selecting only stars having proper motions consistent with the orbit of the cluster yield a detection significance ~10 sigma. While we find a possible continuation of the stream to ~85 degrees, increasing foreground contamination combined with a greater predicted stream distance make it difficult to detect with current data even if the stream continues unabated. The non-uniform distribution of stars in the stream appears to be consistent with episodic tidal stripping, with the most recently shed stars now trailing the cluster by tens of degrees. We provide a table of the highest-ranked candidate stream stars for ongoing and future spectroscopic surveys.