{
  "id": "1607.08253",
  "version": "v1",
  "published": "2016-07-27T20:03:28.000Z",
  "updated": "2016-07-27T20:03:28.000Z",
  "title": "CO-dark gas and molecular filaments in Milky Way-type galaxies - II: The temperature distribution of the gas",
  "authors": [
    "Simon C. O. Glover",
    "Rowan J. Smith"
  ],
  "comment": "17 pages, 17 figures. Accepted by MNRAS",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We investigate the temperature distribution of CO-dark molecular hydrogen (H2) in a series of disk galaxies simulated using the AREPO moving-mesh code. In conditions similar to those in the Milky Way, we find that H2 has a flat temperature distribution ranging from 10 - 100 K. At $T < 30$ K the gas is almost fully molecular and has a high CO content, whereas at $T > 30$ K, the H2 fraction spans a broader range and the CO content is small, allowing us to classify gas in these two regimes as CO-bright and CO-dark, respectively. The mean sound speed in the CO-dark H2 is 0.64 km/s, significantly lower than the value in the cold atomic gas (1.15 km/s), implying that the CO-dark molecular phase is more susceptible to turbulent compression and gravitational collapse than its atomic counterpart. We further show that the temperature of the CO-dark H2 is highly sensitive to the strength of the interstellar radiation field, but that conditions in the CO-bright H2 remain largely unchanged. Finally, we examine the usefulness of the [CII] and [OI] fine structure lines as tracers of the CO-dark gas. We show that in Milky Way-like conditions, diffuse [CII] emission from this gas should be detectable. However, it is a problematic tracer of this gas, as there is only a weak correlation between the brightness of the emission and the H2 surface density. The situation is even worse for the [OI] line, which shows no correlation with the H2 surface density.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-07-27T20:03:28.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "milky way-type galaxies",
      "co-dark gas",
      "molecular filaments",
      "h2 surface density",
      "co-dark molecular"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}