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Accepted manuscript

Streams and Shells Decoded: A Density‑Driven Approach to Stellar Clustering in Galactic Halos with AstroLink

Published online by Cambridge University Press:  22 August 2025

Viraj Ekanayaka*
Affiliation:
Joint First Author Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006, Australia
Smrithi Gireesh Babu
Affiliation:
Joint First Author Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006, Australia
William H. Oliver
Affiliation:
Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Universität Heidelberg, Im Neuenheimer Feld 205, D‑69120 Heidelberg, Germany Zentrum für Astronomie, Institut für Theoretische Astrophysik, Universität Heidelberg, Albert‑Ueberle‑Straße 2, D‑69120 Heidelberg, Germany
Geraint F. Lewis
Affiliation:
Sydney Institute for Astronomy, School of Physics A28, The University of Sydney, NSW 2006, Australia
*
Author for correspondence: Viraj Ekanayaka, Email: naduran.ekanayakagedon@sydney.edu.au.
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Abstract

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We present a novel method to differentiate stream-like and shell-like tidal remnants of stellar systems in galactic halos using the density-based approach of the clustering algorithm AstroLink. While previous studies lean on observation, phase-space, and action-space based criteria for stream and shell determination, we introduce AstroLink’s ordered-density plot and cluster identification as a viable tool for classification. For a given data set, the AstroLink ordered-density plot reveals the density-based hierarchical clustering structure from which the resultant clusters are identified as being statistically significant overdensities. Using simulations of sub-halo disruptions in an external potential to generate samples of tidal structures, we find that the curvature of the ordered-density plot is positive for stream-like structures and negative for shell-like structures. Comparisons with more standard classification techniques reveal strong agreement on which structures typically fit into stream-like and shell-like categories. Furthermore, we investigate the properties of clustered stream and shell samples in radial phase space and energy-angle space. Given the sensitivity of stellar tidal structures to their host dark matter halos, the identification and subsequent classification of these structures provide exciting avenues of investigation in galactic evolution dynamics and dark matter structure formation.

Information

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Astronomical Society of Australia