Black Hole Mass And Eddington Ratio Distribution Functions Of X-Ray-Selected Broad-Line AGNs At Z Similar To 1.4 In The Subaru XMM-Newton Deep Field

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Nobuta, K.
Akiyama, M.
Ueda, Y.
Watson, M. G.
Silverman, J.
Hiroi, K.
Ohta, K.
Iwamuro, F.
Yabe, K.
Tamura, N.

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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 similar to 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 angstrom monochromatic luminosity. We supplement the Mg II FWHM values with the H alpha 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-max method. 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 10(8) M-circle dot but 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.


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Nobuta, K., M. Akiyama, Y. Ueda, M. G. Watson, J. Silverman, K. Hiroi, K. Ohta et al. "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." The Astrophysical Journal, Vol. 761, No. 2 (Dec., 2012): 143.