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The lick AGN monitoring project: Velocity-delay maps from the maximum-entropy method for Arp 151
The Astrophysical Journal Letters
  • Misty C. Bentz, University of California - Irvine
  • Keith Horne, University of St. Andrews
  • Aaron J. Barth, University of California - Irvine
  • Vardha Nicola Bennert, University of California - Santa Barbara
  • Gabriela Canalizo, University of California - Riverside
  • Alexei V. Filippenko, University of California - Berkeley
  • Elinor L. Gates, Lick Observatory
  • Matthew A. Malkan, University of California - Los Angeles
  • Takeo Minezaki, University of Tokyo
  • Tommaso Treu, University of California - Santa Barbara
  • Jong-Hak Woo, Seoul National University
  • Jonelle L. Walsh, University of California - Irvine
Publication Date
9-1-2010
Abstract

We present velocity-delay maps for optical H I, He I, and He II recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. H I response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similar morphologies but exhibit radial stratification, with progressively longer delays for Hγ to Hβ to Hα. The He I and He II response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: free-falling gas and a half-illuminated disk with a hot spot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial outflows are also largely ruled out by the observed asymmetry. A warped-disk geometry provides a physically plausible mechanism for the asymmetric illumination and hot spot features. Simple estimates show that a disk in the broad-line region of Arp 151 could be unstable to warping induced by radiation pressure. Our results demonstrate the potential power of detailed modeling combined with monitoring campaigns at higher cadence to characterize the gas kinematics and physical processes that give rise to the broad emission lines in active galactic nuclei.

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Publisher statement
Published by IOP Publishing.
Citation Information
Misty C. Bentz, Keith Horne, Aaron J. Barth, Vardha Nicola Bennert, et al.. "The lick AGN monitoring project: Velocity-delay maps from the maximum-entropy method for Arp 151" The Astrophysical Journal Letters Vol. 720 Iss. 1 (2010) p. L46 - L51
Available at: http://works.bepress.com/vbennert/25/