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Published July 20, 2009 | Published
Journal Article Open

Observational limits on type 1 active galactic nucleus rate in COSMOS


We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H β, Mg ii, and C iv emission lines in the redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the accretion rate using an Eddington ratio LI/L_(Edd) estimated from optical and X-ray data.We find that very few Type 1 AGNs accrete below LI/L_(Edd) ∼ 0.01, despite simulations of synthetic spectra which show that the survey is sensitive to such Type 1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with LI/L_(Edd) ∼ 0.1.

Additional Information

© 2009 The American Astronomical Society. Received 2009 February 17, accepted for publication 2009 May 7 Published 2009 June 30. We thank Brad Peterson for helpful discussions on emission line measurements and Misty Bentz for comments on host contamination. We thank Marianne Vestergaard for providing the Fe templates and for discussions on the scaling relations. Amy Stutz and Aleks Diamond-Stanic provided useful discussions on statistics. J.R.T acknowledges support from NSF ADP grant NNX08AJ28G and an ARCS fellowship. B.C.K acknowledges support from NASA through Hubble Fellowship grant #HF-01220.01 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.

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