{
  "id": "astro-ph/9804320",
  "version": "v1",
  "published": "1998-04-29T13:08:46.000Z",
  "updated": "1998-04-29T13:08:46.000Z",
  "title": "Properties of Atomic Gas in Spiral Galaxies",
  "authors": [
    "Robert Braun"
  ],
  "comment": "8 page LaTeX requires cupconf.sty, 8 PS figures. Invited review to be published in Interstellar Turbulence, eds. Pepe Franco and Alberto Carraminana",
  "categories": [
    "astro-ph"
  ],
  "abstract": "(Abridged) Although both Warm (WNM, 10^4 K) and Cool (CNM, about 100 K) atomic phases coexist in many environments, the dominant mass contribution within a galaxy's star-forming disk (R_25) is that of the CNM. Mass fractions of 60 to 90% are found within R_25, in the form of moderately opaque filaments with a face-on surface covering factor 15%. The kinetic temperature of the CNM increases systematically with galactocentric radius, from some 50 to 200 K, as expected for a radially declining thermal pressure in the galaxy mid-plane. Galaxies of different Hubble type form a nested distribution in T_K(R), apparently due to the mean differences in pressure which result from the different stellar and gas surface densities. The opaque CNM disappears abruptly near R_25, where the low thermal pressure can no longer support the condensed atomic phase. The CNM is apparently a prerequisite for star formation. Median line profiles of the CNM display an extremely narrow line core (FWHM about 6 km/s) together with broad Lorentzian wings (FWHM about 30 km/s). The line core is consistent with only opacity broadening of a thermal profile. The spatial distribution of CNM linewidths is not random. High linewidths occur in distinct shell-like structures with diameter of 100's of pc to kpc's, which show some correlation with diffuse H-alpha shells. The primary source of ``turbulent'' linewidth in the atomic ISM appears to be organized motions due to localized energy injection on a scale of a few 100 pc.",
  "revisions": [
    {
      "version": "v1",
      "updated": "1998-04-29T13:08:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "spiral galaxies",
      "atomic gas",
      "atomic phase",
      "thermal pressure",
      "properties"
    ],
    "tags": [
      "review article"
    ],
    "note": {
      "typesetting": "LaTeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 489056
    }
  }
}