Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 20, 2011 | Published
Journal Article Open

Accretion Rate and the Physical Nature of Unobscured Active Galaxies


We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L _(int)) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L _(int)/L _(Edd) > 10^(–2)), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L _(int)/L _(Edd) < 10^(–2)) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L _(int)/L _(Edd) < 10^(–2) narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L _(int)/L _(Edd) > 10^(–2) broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L _(int)/L _(Edd) < 10^(–2) AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical "axis" of AGN unification, as described by a simple model.

Additional Information

© 2011 The American Astronomical Society. Received 2010 July 8; accepted 2011 March 2; published 2011 May 5. Based on observations with the XMM-Newton satellite, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the Magellan telescope, operated by the Carnegie Observatories; the ESO Very Large Telescope; and the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution; the Subaru Telescope, operated by the National Astronomical Observatory of Japan; and the NASA/ESA Hubble Space Telescope, operated at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555. J.R.T. acknowledges support from NSF/DDEP grant 0943995, and with C.D.I. acknowledges support from NSF grant AST-0908044. B.C.K. acknowledges support from NASA through Hubble Fellowship grant HF-51243.01, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Gordon Richards and Pat Hall provided useful comments on the manuscript, and we thank the anonymous referee for thorough suggestions that greatly improved the clarity of this work.

Attached Files

Published - Trump2011p13975Astrophys_J.pdf


Files (778.4 kB)
Name Size Download all
778.4 kB Preview Download

Additional details

August 22, 2023
October 23, 2023