Tidal Tails of Nearby Open Clusters. II. A Review of Simulated Properties and the Reliability of Observational Catalogues

Abstract

Context: Recent studies using Gaia data have reported tidal tail detections for tens to hundreds of open clusters. However, a comprehensive assessment of the reliability & completeness of these detections is lacking. Aims: This work aims to summarise the expected properties of tidal tails based on N-body simulations, review the reliability of tidal tail detections in the literature, and grade them according to a set of diagnostic tests. Methods: We used a grid of 68-20000 Msun simulated clusters & analysed the formation & evolution of the tails. We compiled 122 catalogues (58 unique clusters) from literature, within 500 pc of the Sun. We employed tests based on photometric, morphological & dynamical signatures, & comparisons with simulations, to grade their tails. Results: Based on the simulations, we analysed the complex morphology of the tails & their properties (e.g., size, span, stellar types, number density, & mass function) at various cluster masses & ages. During the first 200 Myr of evolution, the tails typically form a characteristic S shape, with an amplitude that scales with cluster mass. The tail span increases at a rate of 4 times the initial velocity dispersion, & the near-tail is predominantly populated by recent escapees. Conclusions: In the 122 published tail catalogues, we found that 15 gold & 55 silver catalogues passed the majority of the tests. The remaining 51 were graded as bronze; care should be taken before using these for further analysis. The age, metallicity, binary fraction, & mass function of stars in the tails were generally consistent with those of their parent clusters. The gold/silver catalogues (69 catalogues of 40 clusters) represent reliable samples for detailed analyses of tails. Future data will be essential for further validation & for leveraging tidal tails as tracers of cluster dissolution & the Galactic potential.