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arXiv · 2610.20726

A model for the ongoing subcluster interaction in Centaurus

Felipe S. Lohmann·Magda Arnaboldi·Michael Hilker·Andreas Burkert·Marilena Spavone·Ortwin Gerhard·Marina Rejkuba·Steffen Mieske·Tom Richtler·Marco Mirabile·Michele Cantiello·Enrichetta Iodice·Sara Federle
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Abstract

Intracluster globular clusters (GCs) preserve the hierarchical and chemical history of galaxy cluster assembly. The nearby Centaurus cluster is believed to be undergoing an interaction between two subclusters, Cen 30 and Cen 45, which should leave an imprint on its intracluster GCs. We aim to characterise the GC population in Centaurus and constrain its recent assembly history, ultimately constructing an interaction scenario consistent with the observational evidence. Using deep VLT/FORS imaging in the $V$ and $I$ bands, we select GC candidates around the cluster centre based on morphology and colour criteria. We use a Voronoi tessellation approach to study the GC spatial distribution and density profiles, demonstrating its advantages over traditional annuli-based methods. We then constrain the evolution of the galaxy luminosity function using the GC specific frequency and colour distribution. The GC spatial distribution shows significant substructure. As in other clusters, red GCs are concentrated on the brightest galaxies, whereas blue GCs trace a more extended structure. We confirm and quantify the previously reported 'bridge' of GCs connecting NGC 4696 and NGC 4709, showing that it hosts twice as many GCs as expected from the projected GC systems of the two galaxies alone. The inferred evolution of the galaxy luminosity function agrees with previous results for Hydra I, yielding a faint-end slope of $α=-1.87_{-0.06}^{+0.06}$ for the galaxy population that assembled the Centaurus core. We propose a nearly head-on collision scenario in which Cen 45 recently passed through Cen 30, with the two subclusters moving approximately along the line of sight. This scenario explains the large line-of-sight velocity difference between the subclusters, the hot X-ray-emitting gas between them, the GC bridge, and the puffed-up GC system of NGC 4709.

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Felipe S. Lohmann, Magda Arnaboldi, Michael Hilker, Andreas Burkert, Marilena Spavone, Ortwin Gerhard, Marina Rejkuba, Steffen Mieske, Tom Richtler, Marco Mirabile, Michele Cantiello, Enrichetta Iodice, Sara Federle. 2026-10-14. A model for the ongoing subcluster interaction in Centaurus. https://arxiv.org/abs/2610.20726

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