{
  "id": "1708.05359",
  "version": "v1",
  "published": "2017-08-17T16:39:22.000Z",
  "updated": "2017-08-17T16:39:22.000Z",
  "title": "The Infrared and Radio Fluxes Densities of Galactic HII Regions",
  "authors": [
    "Z. Makai",
    "L. D. Anderson",
    "J. L. Mascoop",
    "B. Johnstone"
  ],
  "comment": "27 pages, 16 figures, 5 tables",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We derive infrared and radio flux densities of all ~1000 known Galactic HII regions in the Galactic longitude range 17.5 < l < 65 degree. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic \\hii regions \\citep{anderson2014}. We compute flux densities at six wavelengths in the infrared (GLIMPSE 8 microns, WISE 12 microns and 22 microns, MIPSGAL 24 microns, and Hi-GAL 70 microns and 160 microns) and two in the radio (MAGPIS 20 cm and VGPS 21 cm). All HII region infrared flux densities are strongly correlated with their ~20 cm flux densities. All HII regions used here, regardless of physical size or Galactocentric radius, have similar infrared to radio flux density ratios and similar infrared colors, although the smallest regions ($r<1\\,$pc), have slightly elevated IR to radio ratios. The colors $\\log_{10}(F_{24 micron}/F_{12 micron}) \\ge 0$ and $\\log_{10}(F_{70 micron}/F_{12 micron}) \\ge 1.2$, and $\\log_{10}(F_{24 micron}/F_{12 micron}) \\ge 0$ and $\\log_{10}(F_{160 micron}/F_{70 micron}) \\le 0.67$ reliably select HII regions, independent of size. The infrared colors of ~22$\\%$ of HII regions, spanning a large range of physical sizes, satisfy the IRAS color criteria of \\citet{wood1989} for HII regions, after adjusting the criteria to the wavelengths used here. Since these color criteria are commonly thought to select only ultra-compact HII regions, this result indicates that the true ultra-compact HII region population is uncertain. Comparing with a sample of IR color indices from star-forming galaxies, HII regions show higher $\\log_{10}(F_{70 micron}/F_{12 micron})$ ratios. We find a weak trend of decreasing infrared to ~20 cm flux density ratios with increasing $R_{gal}$, in agreement with previous extragalactic results, possibly indicating a decreased dust abundance in the outer Galaxy.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-08-17T16:39:22.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galactic hii regions",
      "radio fluxes densities",
      "ultra-compact hii region population",
      "region infrared flux densities",
      "flux density ratios"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 27,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}