BLACK HOLE MASS AND EDDINGTON RATIO DISTRIBUTION FUNCTIONS OF X-RAY-SELECTED BROAD-LINE AGNs ATz∼ 1.4 IN THE SUBARUXMM-NEWTONDEEP FIELD

Abstract

In order to investigate the growth of super-massive black holes (SMBHs), we construct the black hole mass function (BHMF) and Eddington ratio distribution function (ERDF) of X-ray-selected broadline AGNs at z ∼ 1.4 in the Subaru XMM-Newton Deep Survey (SXDS) field. In this redshift range, a significant part of the accretion growth of SMBHs is thought to be taking place. Black hole masses of X-ray-selected broad-line AGNs are estimated using the width of the broad Mg II line and the 3000Å 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 BHMF and ERDF 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 BHMF and ERDF 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, the corrected BHMF at z = 1.4 has a higher number density above 10 8 M ⊙ but a lower number density below that mass range. The evolution may be indicative of a down-sizing trend of accretion activity among the SMBH population. The evolution of broad-line AGN ERDF from z = 1.4 to 0 indicates that the fraction of broad-line AGNs with accretion rate close to the Eddington-limit is higher at higher redshifts.

The cosmic growth of the active black hole population at 1 <z <2 in zCOSMOS, VVDS and SDSS

“…17, we normalized the ERDF by integrating the BHMF only until log M• = 8, to alleviate the difference in normalization due to the BHMF difference at lower M• . At log λ < −1, our work agrees well with Nobuta et al (2012), while they predict a much larger space density at higher λ. This is probably caused by the larger uncertainty at the high-λ end, employing only the SXDS survey, and the fact that they have not accounted for the virial mass uncertainty in their fit, as we have done here.…”

“…The maximum likelihood results from Nobuta et al (2012) show larger differences. The BHMF agrees well within 8.5 < log M• < 9.5.…”

“…Recently, Nobuta et al (2012) used the SXDS to determine the BHMF and ERDF at z ∼ 1.4, employing the luminosity-weighted 1/Vmax method and the maximum likelihood method from Schulze & Wisotzki (2010). Their sample is X-ray selected and extends significantly deeper than SDSS (4 × 10 −15 erg s −1 cm −2 in the soft band), over an area of ∼ 1.0 deg 2 .…”

“…To resolve these limitations and probe the BHMF and ERDF to lower masses and λ, deep AGN surveys have to be used. Nobuta et al (2012) presented the BHMF and ERDF at z ∼ 1.4 based on an X-ray-selected sample from the Subaru XMM-Newton Deep Survey (SXDS; Ueda et al 2008), utilizing the maximum likelihood method of Schulze & Wisotzki (2010). Since deep surveys with spectroscopic follow-up are currently limited to small areas, they did not probe the bright end of the LF.…”

PRIMUS: AN OBSERVATIONALLY MOTIVATED MODEL TO CONNECT THE EVOLUTION OF THE ACTIVE GALACTIC NUCLEUS AND GALAXY POPULATIONS OUT TOz∼ 1

“…Recent studies (e.g., Schulze & Wisotzki 2010;Kelly & Shen 2013;Nobuta et al 2012) have presented measurements of the SMBH mass functions and ERDFs of Type 1 AGNs that model the completeness effects and biases of optical surveys. While such studies provide vital insight into the Type 1 AGN population, direct comparisons to our model are not possible as the Type 2 AGNs and low accretion rate sources dominate the space densities in most regimes.…”