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| Main Authors: | , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2508.19643 |
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| _version_ | 1866914008886411264 |
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| author | Udagawa, Ken Oka, Tomoharu Yokozuka, Hiroki Kotani, Tatsuya |
| author_facet | Udagawa, Ken Oka, Tomoharu Yokozuka, Hiroki Kotani, Tatsuya |
| contents | We report the discovery of a vertical velocity anomaly (VVA) in the stellar component of the Galactic disk, consistent with the impact of a dark, ultra-compact dwarf galaxy (UCD)-sized object plunging into the Milky Way. The anomaly spatially coincides with a suite of gaseous disturbances -- including an \Hone\ void, a molecular shell (CO 16.134--0.553), and a vertical \Hone\ filament -- previously interpreted as signatures of a dark matter subhalo (DMSH) collision. Analysis of Gaia DR2 astrometry reveals a statistically significant vertical velocity dip co-located with these features, supporting a dynamical origin. The absence of a luminous source at the filament's terminus suggests a dark or failed UCD. These results provide rare observational evidence for a low-mass DMSH, with implications for the substructure of dark matter halos and constraints on the $Λ$CDM model. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_19643 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Signature of a Dark Ultra-compact Dwarf Galaxy Transiting the Milky Way Disk Udagawa, Ken Oka, Tomoharu Yokozuka, Hiroki Kotani, Tatsuya Astrophysics of Galaxies We report the discovery of a vertical velocity anomaly (VVA) in the stellar component of the Galactic disk, consistent with the impact of a dark, ultra-compact dwarf galaxy (UCD)-sized object plunging into the Milky Way. The anomaly spatially coincides with a suite of gaseous disturbances -- including an \Hone\ void, a molecular shell (CO 16.134--0.553), and a vertical \Hone\ filament -- previously interpreted as signatures of a dark matter subhalo (DMSH) collision. Analysis of Gaia DR2 astrometry reveals a statistically significant vertical velocity dip co-located with these features, supporting a dynamical origin. The absence of a luminous source at the filament's terminus suggests a dark or failed UCD. These results provide rare observational evidence for a low-mass DMSH, with implications for the substructure of dark matter halos and constraints on the $Λ$CDM model. |
| title | Signature of a Dark Ultra-compact Dwarf Galaxy Transiting the Milky Way Disk |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2508.19643 |