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arXiv · 2606.02074

Hierarchical assembly in action: a galaxy tail from a disrupting group in the Virgo cluster outskirts

J. Alfonso L. Aguerri·Stefano Zarattini·Virginia Cuomo·Lorenzo Morelli
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Abstract

Group environments are thought to play a key role in shaping galaxy evolution prior to cluster accretion. However, direct observational evidence linking group--cluster interactions to the transformation of low-mass galaxies remains scarce. We reexamine the nature and origin of the W cloud, located in the southern outskirts of the Virgo cluster, to better understand the dynamical processes driving group accretion and galaxy transformation during cluster assembly. Using the spatial distribution, kinematics, and stellar population properties of galaxies in the W cloud and its surroundings, we characterize the three-dimensional structure and dynamical state of the system. We show that the W cloud is not a large-scale filament seen in projection, but is instead dominated by a compact galaxy group (the W group) currently interacting with Virgo. We also identify a previously unknown, dynamically coherent tail of galaxies (the W tail) connecting the W group to the cluster. The tail exhibits a continuous sequence in velocity, velocity dispersion, and three-dimensional distance. Its low-velocity component is already gravitationally bound to Virgo, whereas higher-velocity galaxies remain associated with the W group and are still infalling. The W tail forms a planar structure aligned with the orbital geometry of the W group, strongly supporting a tidal origin. The stellar masses and colours of its members indicate that the stripped population is dominated by low-mass, star-forming dwarf galaxies that remain in the blue cloud. The W group--W tail system provides a well-resolved example of an ongoing group--cluster interaction, illustrating how low-density groups can deliver largely unprocessed dwarf galaxies into clusters. This system provides important observational constraints on the hierarchical assembly of galaxy clusters and the buildup of their dwarf galaxy populations.

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J. Alfonso L. Aguerri, Stefano Zarattini, Virginia Cuomo, Lorenzo Morelli. 2026-06-01. Hierarchical assembly in action: a galaxy tail from a disrupting group in the Virgo cluster outskirts. https://arxiv.org/abs/2606.02074

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