{
  "id": "1612.02196",
  "version": "v1",
  "published": "2016-12-07T11:13:31.000Z",
  "updated": "2016-12-07T11:13:31.000Z",
  "title": "Dense gas in low-metallicity galaxies",
  "authors": [
    "J. Braine",
    "Y. Shimajiri",
    "P. André",
    "S. Bontemps",
    "Yu Gao",
    "Hao Chen",
    "C. Kramer"
  ],
  "comment": "9 pages, 13 figures, A&A in press",
  "journal": "A&A 2016",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Stars form out of the densest parts of molecular clouds. Far-IR emission can be used to estimate the Star Formation Rate (SFR) and high dipole moment molecules, typically HCN, trace the dense gas. A strong correlation exists between HCN and Far-IR emission, with the ratio being nearly constant, over a large range of physical scales. A few recent observations have found HCN to be weak with respect to the Far-IR and CO in subsolar metallicity (low-Z) objects. We present observations of the Local Group galaxies M33, IC10, and NGC6822 with the IRAM 30meter and NRO 45m telescopes, greatly improving the sample of low-Z galaxies observed. HCN, HCO$^+$, CS, C$_2$H, and HNC have been detected. Compared to solar metallicity galaxies, the Nitrogen-bearing species are weak (HCN, HNC) or not detected (CN, HNCO, N$_2$H$^+$) relative to Far-IR or CO emission. HCO$^+$ and C$_2$H emission is normal with respect to CO and Far-IR. While $^{13}$CO is the usual factor 10 weaker than $^{12}$CO, C$^{18}$O emission was not detected down to very low levels. Including earlier data, we find that the HCN/HCO$^+$ ratio varies with metallicity (O/H) and attribute this to the sharply decreasing Nitrogen abundance. The dense gas fraction, traced by the HCN/CO and HCO$^+$/CO ratios, follows the SFR but in the low-Z objects the HCO$^+$ is much easier to measure. Combined with larger and smaller scale measurements, the HCO$^+$ line appears to be an excellent tracer of dense gas and varies linearly with the SFR for both low and high metallicities.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-12-07T11:13:31.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "dense gas",
      "low-metallicity galaxies",
      "far-ir emission",
      "local group galaxies m33",
      "high dipole moment molecules"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}