{
  "id": "1407.0909",
  "version": "v2",
  "published": "2014-07-03T13:10:13.000Z",
  "updated": "2014-09-04T04:03:31.000Z",
  "title": "Dust in Active Galactic Nuclei: Anomalous Silicate to Optical Extinction Ratios?",
  "authors": [
    "Jianwei Lyu",
    "Lei Hao",
    "Aigen Li"
  ],
  "comment": "ApJL, 792, L9, in print",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "Dust plays a central role in the unification theory of active galactic nuclei (AGNs). However, little is known about the nature (e.g., size, composition) of the dust which forms a torus around the AGN. In this Letter we report a systematic exploration of the optical extinction (A_V) and the silicate absorption optical depth (\\Delta\\tau9.7) of 110 type 2 AGNs. We derive A_V from the Balmer decrement based on the Sloan Digital Sky Survey data, and \\Delta\\tau9.7 from the Spitzer/Infrared Spectrograph data. We find that with a mean ratio of A_V/\\Delta\\tau9.7 ~ 5.5, the optical-to-silicate extinction ratios of these AGNs are substantially lower than that of the Galactic diffuse interstellar medium (ISM) for which A_V/\\Delta\\tau9.7 ~ 18.5. We argue that the anomalously low A_V/\\Delta\\tau9.7 ratio could be due to the predominance of larger grains in the AGN torus compared to that in the Galactic diffuse ISM.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-07-03T13:10:13.000Z",
      "abstract": "Dust plays a central role in the unification theory of active galactic nuclei (AGNs). However, little is known about the nature (e.g., size, composition) of the dust which forms a torus around the AGN. In this Letter we report a systematic exploration of the optical extinction (A_V) and the silicate absorption optical depth (\\Delta\\tau9.7) of 110 type 2 AGNs. We derive A_V from the Balmer decrement based on the SDSS data, and \\Delta\\tau9.7 from the Spitzer/IRS data. We find that, with a mean ratio of A_V/\\Delta\\tau9.7 ~ 5.5, the optical to silicate extinction ratios of these AGNs are substantially lower than that of the Galactic diffuse interstellar medium (ISM) for which A_V/\\Delta\\tau9.7 ~ 18.5. We argue that the anomalously low A_V/\\Delta\\tau9.7 ratio could be due to the predominance of larger grains in the AGN torus compared to that in the Galactic diffuse ISM.",
      "comment": "submitted to ApJL, the current version is revised accommodating two rounds of the referee's reports",
      "journal": null,
      "doi": null
    },
    {
      "version": "v2",
      "updated": "2014-09-04T04:03:31.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "active galactic nuclei",
      "optical extinction ratios",
      "anomalous silicate",
      "galactic diffuse interstellar medium",
      "galactic diffuse ism"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/2041-8205/792/1/L9",
      "journal": "The Astrophysical Journal",
      "year": 2014,
      "month": "Sep",
      "volume": 792,
      "number": 1
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1304663,
      "adsabs": "2014ApJ...792L...9L"
    }
  }
}