Issue |
A&A
Volume 689, September 2024
|
|
---|---|---|
Article Number | L3 | |
Number of page(s) | 5 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202451289 | |
Published online | 30 August 2024 |
Letter to the Editor
Gas-rich “ultra-diffuse” galaxies are consistent with the baryonic Tully–Fisher relation and with Milgromian dynamics
INAF – Arcetri Astrophysical Observatory, Viale Enrico Fermi 5, 50125 Florence, Italy
Received:
27
June
2024
Accepted:
12
July
2024
Some gas-rich “ultra-diffuse” galaxies (UDGs), which are extreme examples of low surface brightness (LSB) dwarf galaxies, have been reported to lack dark matter and to be offset from the baryonic Tully–Fisher relation (BTFR). If confirmed, these UDGs would represent a serious challenge for both ΛCDM galaxy-formation models and Milgromian dynamics. Here I demonstrate that these conclusions are very dubious due to underestimated uncertainties on inclinations and/or distances. First, I show that UDGs are offset from the BTFR in the same way as usual face-on LSB dwarfs due to systematic biases at low inclinations. Next, I analyze the two UDGs with the best available rotation-curve data. The first (AGC 242019) is ideally inclined for kinematic studies; MOND can fit the observed rotation curve with a distance of 12.5 ± 0.6 Mpc, which is consistent with Virgocentric flow models. The second UDG (AGC 114905) is close to face-on, so not ideal for kinematic studies; MOND can fit the observed rotation curve with a distance of 68 ± 13 Mpc and inclination of 15° ±2°, which are consistent with existing data. In particular, I show that the disk inclination is more uncertain than previously estimated due to significant asymmetries (lopsidedness) in the stellar distribution. In conclusion, there is no strong evidence that gas-rich UDGs and gas-rich LSB dwarfs are distinct galaxy populations with different dynamical properties; instead, UDGs seem to be a subset of LSB dwarf galaxies biased toward face-on systems.
Key words: gravitation / galaxies: dwarf / galaxies: evolution / galaxies: kinematics and dynamics / dark matter
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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