{
  "id": "1702.03331",
  "version": "v1",
  "published": "2017-02-10T21:43:01.000Z",
  "updated": "2017-02-10T21:43:01.000Z",
  "title": "ALMA hints at the existence of an unseen reservoir of diffuse molecular gas in the Galactic bulge",
  "authors": [
    "M. Gerin",
    "H. Liszt"
  ],
  "comment": "Accepted for Astronomy & Astrophysics",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Aims. We aim to understand the unexpected presence of mm-wave molecular absorption at -200 \\kms $< {\\rm v} < -140$ \\kms\\ in a direction that is well away from regions of the Galactic bulge where CO emission at such velocities is prominent. Methods. We compared 89 GHz Cycle 2 ALMA absorption spectra of \\hcop, HCN, and HNC toward the extragalactic continuum source B1741-312 at l=-2.14\\degr, b=-1.00\\degr\\ with existing CO, H I, and dust emission and absorption measurements. We placed the atomic and molecular gas in the bulge and disk using circular and non-circular galactic kinematics, deriving N(H I) from a combination of 21cm emission and absorption and we derive N(\\HH) from scaling of the \\hcop\\ absorption. We then inverted the variation of near-IR reddening E(J-K) with distance modulus and scale E(J-K) to a total gas column density N(H) that may be compared to N(H I) and N(\\HH). Results. At galactocentric radii \\Rgal\\ $>$ 1.5 kpc, conventional measures such as the standard CO-\\HH\\ conversion factor and locally observed N(\\hcop)/N(\\HH) ratio separately imply that H I and \\HH\\ contribute about equally to N(H), and the gas-derived N(H) values are in broad agreement with those derived from E(J-K). Within the Galactic bulge at \\Rgal $<$ 1.5 kpc, H I contributes less than 10\\% of the material inferred from E(J-K), so that the molecular absorption detected here is needed to understand the extinction.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-02-10T21:43:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galactic bulge",
      "diffuse molecular gas",
      "unseen reservoir",
      "alma hints",
      "total gas column density"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}