Exploring the formation mechanisms of tidal structures in globular clusters of extragalactic origin

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Abstract
Tidal structures around globular clusters provide valuable insights into cluster evolution and the hierarchical assembly of the Milky Way. Using wide-field imaging data from the DESI Legacy Survey combined with a color-magnitude matched-filter technique, we performed a systematic analysis of extratidal features in 28 Galactic globular clusters of likely extragalactic origin, representing the largest homogeneous sample examined in this context to date. The clusters display diverse morphologies: 12 exhibit tidal tails, nine show diffuse envelopes, and seven reveal no clear extratidal features. Notably, we report the first detection of an extended tidal structure around the Sagittarius-associated cluster Terzan 7. To explore the underlying drivers, we compared intrinsic properties, orbital dynamics, and possible accretion associations across morphological groups. From the parameter distributions, complemented by Kolmogorov-Smirnov tests, we find that total mass, escape velocity, concentration, tidal filling factor, pericentric radius, eccentricity, and radial angle in action-angle coordinates are all likely group-sensitive parameters. These results suggest that both internal cluster properties and orbital configurations play important roles in shaping extratidal morphologies. In addition, the cluster’s accretion history shows no clear correlation with the presence of tidal features, indicating that it is not a direct driver of outer structure formation. Overall, the diversity of tidal structures is unlikely to be governed by a single factor. Instead, it reflects the interplay between internal dynamical evolution and the external Galactic environment. This study provides the most comprehensive constraints so far on the physical processes driving extratidal structures in accreted globular clusters.
Funding Information
  • National Key Research and Development Program of China (2021YFA1600401)
  • National Key Research and Development Program of China (2021YFA1600400)
  • National Natural Science Foundation of China (12373019)
  • Natural Science Foundation of Beijing Municipality (1232032)
  • Science research grants from the China Manned Space Project (CMS-CSST-2021-B03)
  • Science research grants from the China Manned Space Project (CMS-CSST-2021-A10)
  • Science research grants from the China Manned Space Project (CMS-CSST-2025-A11)
  • National Natural Science Foundation of China (12133002)
  • National Key Research and Development Program of China (2024YFA1611902)

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