{
  "id": "1806.04922",
  "version": "v1",
  "published": "2018-06-13T10:04:20.000Z",
  "updated": "2018-06-13T10:04:20.000Z",
  "title": "Galactic HCO+ Absorption toward Compact Extragalactic Radio Sources",
  "authors": [
    "Geumsook Park",
    "Bon-Chul Koo",
    "Kee-Tae Kim",
    "Do-Young Byun",
    "Carl E. Heiles"
  ],
  "comment": "10 pages, 3 figures; accepted in Astrophysics and Space Science (ASTR-D-18-00258R1)",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "As part of the search for the \"dark molecular gas (DMG),\" we report on the results of HCO$^+$ J = 1-0 absorption observations toward nine bright extragalactic millimeter wave continuum sources. The extragalactic sources are at high Galactic latitudes (|b| > 10$\\deg$) and seen at small extinction (E(B-V) $\\lesssim$ 0.1 mag). We have detected the HCO$^+$ absorption lines toward two sources, B0838+133 and B2251+158. The absorption toward B2251+158 was previously reported, while the absorption toward B0838+133 is a new detection. We derive hydrogen column densities or their upper limits toward the nine sources from our observations and compare them to those expected from CO line emission and far-infrared dust continuum emission. Toward the seven sources with no HCO$^+$ detection, CO emission has not been detected, either. Thus the sight lines are likely to be filled with almost pure atomic gas. Toward the two sources with HCO$^+$ detection, CO emission has been also detected. Comparison of the H$_2$ column densities from HCO$^+$ absorption and CO emission suggests a non-negligible amount of DMG toward B0838+133.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-06-13T10:04:20.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "compact extragalactic radio sources",
      "absorption",
      "bright extragalactic millimeter wave continuum",
      "extragalactic millimeter wave continuum sources",
      "column densities"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}