{
  "id": "1508.03403",
  "version": "v1",
  "published": "2015-08-14T02:09:55.000Z",
  "updated": "2015-08-14T02:09:55.000Z",
  "title": "Very Large Interstellar Grains as Evidenced by the Mid-Infrared Extinction",
  "authors": [
    "Shu Wang",
    "Aigen Li",
    "B. W. Jiang"
  ],
  "comment": "Dedicated to the late Professor J. Mayo Greenberg. 18 pages, 4 figures, accepted for publication in The Astrophysical Journal",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "The sizes of interstellar grains are widely distributed, ranging from a few angstroms to a few micrometers. The ultraviolet (UV) and optical extinction constrains the dust in the size range of a couple hundredth micrometers to several submicrometers. The near and mid infrared (IR) emission constrains the nanometer-sized grains and angstrom-sized very large molecules. However, the quantity and size distribution of micrometer-sized grains remain unknown as they are gray in the UV/optical extinction and they are too cold and emit too little in the IR to be detected by IRAS, Spitzer, or Herschel. In this work, we employ the ~3-8 micron mid-IR extinction which is flat in both diffuse and dense regions to constrain the quantity, size, and composition of the micron-sized grain component. We find that, together with nano- and submicron-sized silicate and graphite (as well as PAHs), micron-sized graphite grains with C/H=137 ppm and a mean size of ~1.2 micron closely fit the observed interstellar extinction of the Galactic diffuse interstellar medium from the far-UV to the mid-IR as well as the near-IR to millimeter thermal emission obtained by COBE/DIRBE, COBE/FIRAS, and Planck up to lambda < 1000 micron. The micron-sized graphite component accounts for ~14.6% of the total dust mass and ~2.5% of the total IR emission.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-08-14T02:09:55.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "large interstellar grains",
      "mid-infrared extinction",
      "galactic diffuse interstellar medium",
      "couple hundredth micrometers",
      "graphite component accounts"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}