{
  "id": "2408.05269",
  "version": "v1",
  "published": "2024-08-09T18:00:02.000Z",
  "updated": "2024-08-09T18:00:02.000Z",
  "title": "Gas-rich \"ultra-diffuse\" galaxies are consistent with the baryonic Tully-Fisher relation and with Milgromian dynamics",
  "authors": [
    "Federico Lelli"
  ],
  "comment": "5 pages, 4 figures, accepted for publication in Astronomy & Astrophysics Letters",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO",
    "gr-qc"
  ],
  "abstract": "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 LCDM 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 UDG (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 degrees, 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-08-09T18:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "baryonic tully-fisher relation",
      "milgromian dynamics",
      "consistent",
      "ultra-diffuse",
      "usual face-on lsb dwarfs"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 5,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}