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arXiv · 2601.16408

Unveiling a Thin Filament of the Cosmic Web in the Ursa Major Supergroup

Jin-Long Xu·Ming Zhu·Peng Jiang·Nai-Ping Yu·Chuan-Peng Zhang·Xiao-Lan Liu·Mei Ai·Yin-Jie Jing·Jie Wang
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Abstract

Filaments are crucial components of the cosmic web, representing the extensive and aligned distributions of galaxies and gas. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report the detection of a filament in the Ursa Major supergroup using atomic-hydrogen (HI) observations. This filament consists of sixteen various types of galaxies and five starless gas clumps, spanning a length of approximately 0.9 Mpc. Notably, it is extremely thin, with a thickness comparable to the diameter of a galaxy. We observed a galaxy-filament spin alignment and a velocity gradient within the filament. These findings strongly suggest a cold accretion flow along the filament, potentially contributing to the formation and growth of the galaxies. The thin filament, as a small group, is likely to be merged into the Ursa Major supergroup in the context of hierarchical structure formation.

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Jin-Long Xu, Ming Zhu, Peng Jiang, Nai-Ping Yu, Chuan-Peng Zhang, Xiao-Lan Liu, Mei Ai, Yin-Jie Jing, Jie Wang. 2026-01-23. Unveiling a Thin Filament of the Cosmic Web in the Ursa Major Supergroup. https://arxiv.org/abs/2601.16408

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