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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 607142.0, MPI für Astronomie / Publikationen_mpia
Spectropolarimetric evidence for radiatively inefficient accretion in an optically dull active galaxy
Authors:Trump, J. R.; Nagao, T.; Ikeda, H.; Murayama, T.; Impey, C. D.; Stocke, J. T.; Civano, F.; Elvis, M.; Jahnke, K.; Kelly, B. C.; Koekemoer, A. M.; Taniguchi, Y.
Date of Publication (YYYY-MM-DD):2011
Journal Abbrev.:The Astrophysical Journal
Issue / Number:1
Audience:Not Specified
Abstract / Description:We present Subaru/FOCAS spectropolarimetry of two active galaxies in the Cosmic Evolution Survey. These objects were selected to be optically dull, with the bright X-ray emission of an active galactic nucleus (AGN) but missing optical emission lines in our previous spectroscopy. Our new observations show that one target has very weak emission lines consistent with an optically dull AGN, while the other object has strong emission lines typical of a host-diluted Type 2 Seyfert galaxy. In neither source do we observe polarized emission lines, with 3σ upper limits of P BLR <~ 2%. This means that the missing broad emission lines (and weaker narrow emission lines) are not due to simple anisotropic obscuration, e.g., by the canonical AGN torus. The weak-lined optically dull AGN exhibits a blue polarized continuum with P = 0.78% ± 0.07% at 4400 Ã… < λrest < 7200 Ã… (P = 1.37% ± 0.16% at 4400 Ã… < λrest < 5050 Ã…). The wavelength dependence of this polarized flux is similar to that of an unobscured AGN continuum and represents the intrinsic AGN emission, either as synchrotron emission or the outer part of an accretion disk reflected by a clumpy dust scatterer. Because this intrinsic AGN emission lacks emission lines, this source is likely to have a radiatively inefficient accretion flow. Based on observations with the Subaru Telescope, operated by the National Astronomical Observatory of Japan.
Free Keywords:accretion; accretion disks; galaxies: active; galaxies: nuclei; polarization; quasars: emission lines; radiation mechanisms: general
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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