Accretion rate and the physical nature of unobscured active galaxies

Jonathan R. Trump, Christopher D. Impey, Brandon C. Kelly, Francesca Civano, Jared M. Gabor, Aleksandar M. Diamond-Stanic, Andrea Merloni, C. Megan Urry, Heng Hao, Knud Jahnke, Tohru Nagao, Yoshi Taniguchi, Anton M. Koekemoer, Giorgio Lanzuisi, Charles Liu, Vincenzo Mainieri, Mara Salvato, Nick Z. Scoville

Research output: Contribution to journalArticlepeer-review

105 Scopus citations


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.

Original languageEnglish (US)
Article number60
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 2011


  • accretion
  • accretion disks
  • galaxies: Seyfert
  • galaxies: active
  • galaxies: nuclei
  • quasars: emission lines
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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