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The nuclear infrared emission of low-luminosity active galactic nuclei

机译：The nuclear infrared emission of low-luminosity active galactic nuclei

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摘要

We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs), and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGNs; L _(bol) ? 10 ~(42) erg s ~(-1)). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGNs, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGNs have not yet been well determined. We separate the present LLAGN sample into three categories depending on their Eddington ratio and radio emission, finding different IR characteristics for each class. (1) At the low-luminosity, low-Eddington-ratio (log L _(bol)/L _(Edd) < -4.6) end of the sample, we identify "host- dominated" galaxies with strong polycyclic aromatic hydrocarbon bands that may indicate active (circum-)nuclear star formation. (2) Some very radio-loud objects are also present at these low Eddington ratios. The IR emission in these nuclei is dominated by synchrotron radiation, and some are likely to be unobscured type 2 AGNs that genuinely lack a broad-line region. (3) At higher Eddington ratios, strong, compact nuclear sources are visible in the MIR images. The nuclear SEDs of these galaxies are diverse; some resemble typical Seyfert nuclei, while others lack a well-defined MIR "dust bump." Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGNs do not host a Seyfert-like obscuring torus. We anticipate that detailed modeling of the new data and SEDs in terms of accretion disk, jet, radiatively inefficient accretion flow, and torus components will provide further insights into the nuclear structures and processes of LLAGNs.

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  • 来源
    《The Astronomical journal》 |2012年第1期|11-1-11-27|共27页
  • 作者

    Mason R.E.; Lopez-Rodriguez E.; Packham C.Alonso-Herrero A.Levenson N.A.Radomski J.Ramosalmeida C.Colina L.Elitzur M.Aretxaga I.Roche P.F.Oi N.;

  • 作者单位

    Gemini Observatory, Northern Operations Center, 670N. A'ohoku Place, Hilo, HI 96720, United States;

    Department of Astronomy, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611, United States;

    Instituto de Física de Cantabria, CSIC-UC, Avenida de los Castros s/n, Santander 39005, SpainGemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena, ChileInstituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205La Laguna, Tenerife, SpainDepartamento de Astrofísica, Centro de Astrobiología (CSIC/INTA), Instituto Nacional de Técnica Aeroespacial, Crta de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, SpainDepartment of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, United StatesInstituto Nacional de Astrofísica, óptica y Electrónica (INAOE), Aptdo. Postal 51 y 216, 72000 Puebla, MexicoAstrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, United KingdomDepartment of Astronomy, School of Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588, Japan;

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  • 原文格式 PDF
  • 正文语种 英语
  • 中图分类 天文学;
  • 关键词

    galaxies: active; galaxies: nuclei; galaxies: photometry; galaxies: Seyfert; infrared: galaxies;

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