{
  "id": "2002.03110",
  "version": "v1",
  "published": "2020-02-08T08:09:04.000Z",
  "updated": "2020-02-08T08:09:04.000Z",
  "title": "Entropy and Mass Distribution in Disc Galaxies",
  "authors": [
    "John Herbert Marr"
  ],
  "comment": "16 pages, 4 figures. Invitation paper for \"Debate on the Physics of Galactic Rotation and the Existence of Dark Matter\". Accepted Jan 2020",
  "journal": "Galaxies 2020, 8, 12",
  "doi": "10.3390/galaxies8010012",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "The relaxed motion of stars and gas in galactic discs is well approximated by a rotational velocity that is a function of radial position only, implying that individual components have lost any information about their prior states. Thermodynamically, such an equilibrium state is a microcanonical ensemble with maximum entropy, characterised by a lognormal probability distribution. Assuming this for the surface density distribution yields rotation curves that closely match observational data across a wide range of disc masses and galaxy types, and provides a useful tool for modelling the theoretical density distribution in the disc. A universal disc spin parameter emerges from the model, giving a tight virial mass estimator with strong correlation between angular momentum and disc mass, suggesting a mechanism by which the proto-disc developed by dumping excess mass to the core, or excess angular momentum to a satellite galaxy. The baryonic-to-dynamic mass ratio for the model approaches unity for high mass galaxies, but is generally $<1$ for low mass discs, and this discrepancy appears to follow a similar relationship to that shown in recent work on the radial acceleration relation (RAR). Although this may support Modified Newtonian Dynamics (MOND) in preference to a dark matter (DM) halo, it does not exclude undetected baryonic mass or a gravitational DM component in the disc.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-02-08T08:09:04.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "mass distribution",
      "disc galaxies",
      "surface density distribution yields rotation",
      "universal disc spin parameter emerges",
      "density distribution yields rotation curves"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}