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 December 20, 2015 | Submitted + Published
Journal Article Open

Eddington ratio Distribution of X-ray selected broad-line AGNs at 1.0 < z < 2.2

Abstract

We investigate the Eddington ratio distribution of X-ray-selected broad-line active galactic nuclei (AGNs) in the redshift range 1.0 < z < 2.2, where the number density of AGNs peaks. Combining the optical and Subaru/Fiber Multi Object Spectrograph near-infrared spectroscopy, we estimate black hole masses for broad-line AGNs in the Chandra Deep Field South (CDF-S), Extended Chandra Deep Field South (E-CDF-S), and the XMM-Newton Lockman Hole (XMM-LH) surveys. AGNs with similar black hole masses show a broad range of AGN bolometric luminosities, which are calculated from X-ray luminosities, indicating that the accretion rate of black holes is widely distributed. We find a substantial fraction of massive black holes accreting significantly below the Eddington limit at z lesssim 2, in contrast to what is generally found for luminous AGNs at high redshift. Our analysis of observational selection biases indicates that the "AGN cosmic downsizing" phenomenon can be simply explained by the strong evolution of the comoving number density at the bright end of the AGN luminosity function, together with the corresponding selection effects. However, one might need to consider a correlation between the AGN luminosity and the accretion rate of black holes, in which luminous AGNs have higher Eddington ratios than low-luminosity AGNs, in order to understand the relatively small fraction of low-luminosity AGNs with high accretion rates in this epoch. Therefore, the observed downsizing trend could be interpreted as massive black holes with low accretion rates, which are relatively fainter than less-massive black holes with efficient accretion.

Additional Information

© 2015 The American Astronomical Society. Received 2014 September 30; accepted 2015 November 1; published 2015 December 21. We thank the anonymous referee for several comments, which helped to improve the quality of the manuscript significantly. We thank Amy Barger for useful comments that helped improve this paper. Facility: Subaru (FMOS). - Subaru Telescope

Attached Files

Published - Suh_2015.pdf

Submitted - 1511.01092v1.pdf

Files

Suh_2015.pdf
Files (7.7 MB)
Name Size Download all
md5:2fcc3de9c2c76595f2c3437b099d279f
2.1 MB Preview Download
md5:76505f9118993616ba98ff46ab49dfd8
5.6 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 17, 2023