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Black hole mass and eddington ratio distribution functions of X-ray-selected broad-line AGNs at z ∼ 1.4 in the Subaru XMM-Newton Deep Field

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  • K. Nobuta
  • M. Akiyama
  • Y. Ueda
  • M. G. Watson
  • J. Silverman
  • K. Hiroi
  • K. Ohta
  • F. Iwamuro
  • K. Yabe
  • N. Tamura
  • Y. Moritani
  • M. Sumiyoshi
  • N. Takato
  • M. Kimura
  • T. Maihara
  • I. Lewis
  • D. Bonfield
  • E. Curtis-Lake
  • E. MacAulay
  • F. Clarke
  • K. Sekiguchi
  • C. Simpson
  • S. Croom
  • M. Ouchi
  • H. Hanami
  • T. Yamada

In order to investigate the growth of supermassive black holes (SMBHs), we construct the black hole mass function (BHMF) and Eddington ratio distribution function (ERDF) of X-ray-selected broad-line active galactic nuclei (AGNs) at z ∼ 1.4 in the Subaru XMM-Newton Deep Survey (SXDS) field. A significant part of the accretion growth of SMBHs is thought to take place in this redshift range. Black hole masses of X-ray-selected broad-line AGNs are estimated using the width of the broad Mg II line and 3000 Å monochromatic luminosity. We supplement the Mg II FWHM values with the Hα FWHM obtained from our NIR spectroscopic survey. Using the black hole masses of broad-line AGNs at redshifts between 1.18 and 1.68, the binned broad-line AGN BHMFs and ERDFs are calculated using the V maxmethod. To properly account for selection effects that impact the binned estimates, we derive the corrected broad-line AGN BHMFs and ERDFs by applying the maximum likelihood method, assuming that the ERDF is constant regardless of the black hole mass. We do not correct for the non-negligible uncertainties in virial BH mass estimates. If we compare the corrected broad-line AGN BHMF with that in the local universe, then the corrected BHMF at z = 1.4 has a higher number density above 108 Mbut a lower number density below that mass range. The evolution may be indicative of a downsizing trend of accretion activity among the SMBH population. The evolution of broad-line AGN ERDFs from z = 1.4 to 0 indicates that the fraction of broad-line AGNs with accretion rates close to the Eddington limit is higher at higher redshifts.

Original languageEnglish
Article number143
JournalAstrophysical Journal
Issue number2
Early online date4 Dec 2012
Publication statusPublished - 20 Dec 2012

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