The Rogue One: A Dark Matter-Dominated Dwarf in the Trail of Dark Matter-Deficient Galaxies

@misc{vaz2026rogue,
  title = {{The Rogue One: A Dark Matter-Dominated Dwarf in the Trail of Dark Matter-Deficient Galaxies}},
  author = {Daniel Vaz and Arsen Levitskiy and Duncan Forbes and Aaron J. Romanowsky and Jonah Gannon and Jean P. Brodie and Yimeng Tang and Kenji Bekki and Warrick J. Couch},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.07467},
  eprint = {2610.07467},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.07467},
}

TY  - UNPB
TI  - The Rogue One: A Dark Matter-Dominated Dwarf in the Trail of Dark Matter-Deficient Galaxies
AU  - Daniel Vaz
AU  - Arsen Levitskiy
AU  - Duncan Forbes
AU  - Aaron J. Romanowsky
AU  - Jonah Gannon
AU  - Jean P. Brodie
AU  - Yimeng Tang
AU  - Kenji Bekki
AU  - Warrick J. Couch
PY  - 2026
DA  - 2026/10/05
PB  - arXiv
DO  - 10.48550/arxiv.2610.07467
UR  - https://arxiv.org/abs/2610.07467
AB  - We present the first measurement of the stellar velocity dispersion of LEDA 4014647, a compact dwarf galaxy spatially aligned with the NGC 1052 trail, a linear chain of dark matter-deficient galaxies (DMDGs) proposed to have formed in a single high-speed dwarf−dwarf collision ∼ 8 Gyr ago. Using integral-field spectroscopy obtained with the Keck Cosmic Web Imager (KCWI), we measure a stellar velocity dispersion of σ= 15.8 ± 2.0 km s^−1 within the half-light radius (R_e). We derive a dynamical mass within the 3D half-light radius of M_dyn(<r_1/2) = (1.5 ± 0.4) × 10^8 M_⊙, a factor of ∼ 3 larger than the enclosed stellar mass, implying a DM fraction of f_DM = 0.7 ± 0.1 at r_1/2. Full-spectrum stellar population fitting yields an old (t ≈ 13 Gyr) and metal-poor ([M/H] ≈ −1.2 dex) stellar population, consistent with independent photometric estimates and predating the proposed collision epoch. LEDA 4014647 is therefore a DM-dominated system, and cannot have formed from the DM-free, shock-compressed gas that produced the proposed trail DMDGs DF2, DF4, and DF9. Its nature, however, remains an open question: while a chance-projection along the trail axis is a possible explanation, its old stellar population, compact morphology, and DM content are also consistent with the surviving collisionless remnant of one of the progenitor dwarfs of the dwarf−dwarf collision. Distinguishing between these two scenarios will ultimately require deeper spectroscopy to tighten the stellar population and DM halo constraints, and targeted N-body and hydrodynamical simulations tracking the post-encounter fate of the progenitors.
ER  -