BASS. XXX. Distribution Functions of DR2 Eddington Ratios, Black Hole Masses, and X-Ray Luminosities

Abstract

We determine the low-redshift X-ray luminosity function, active black hole mass function (BHMF), and Eddington ratio distribution function (ERDF) for both unobscured (Type 1) and obscured (Type 2) active galactic nuclei (AGNs), using the unprecedented spectroscopic completeness of the BAT AGN Spectroscopic Survey (BASS) data release 2. In addition to a straightforward 1/V max approach, we also compute the intrinsic distributions, accounting for sample truncation by employing a forward-modeling approach to recover the observed BHMF and ERDF. As previous BHMFs and ERDFs have been robustly determined only for samples of bright, broad-line (Type 1) AGNs and/or quasars, ours are the first directly observationally constrained BHMF and ERDF of Type 2 AGNs. We find that after accounting for all observational biases, the intrinsic ERDF of Type 2 AGNs is significantly more skewed toward lower Eddington ratios than the intrinsic ERDF of Type 1 AGNs. This result supports the radiation-regulated unification scenario, in which radiation pressure dictates the geometry of the dusty obscuring structure around an AGN. Calculating the ERDFs in two separate mass bins, we verify that the derived shape is consistent, validating the assumption that the ERDF (shape) is mass-independent. We report the local AGN duty cycle as a function of mass and Eddington ratio, by comparing the BASS active BHMF with the local mass function for all supermassive black holes. We also present the log N − log S of the Swift/BAT 70 month sources.

BASS. XXV. DR2 Broad-line-based Black Hole Mass Estimates and Biases from Obscuration

“…The dearth of high-L/L Edd , high-N H AGNs is commonly interpreted as evidence for the amount of obscuring material, and indeed the degree of obscuration, to be driven by radiation pressure exerted by the central engine on the (inner) obscuring toroidal structure (e.g., Fabian et al 2009;Ricci et al 2017b;Ishibashi et al 2018, and references therein). Revisiting the distribution of BASS/DR2 AGNs in the L/L Edd -N H plane, and the relevant physical scenarios, is beyond the scope of the present study and will be addressed in a forthcoming BASS publication (see, however, the results of the companion BASS/DR2 paper by Ananna et al 2022).…”

BAT AGN Spectroscopic Survey XXI: The Data Release 2 Overview

“…A largely statistically complete sample with 99.6% and 98% of the brightest 858 ultrahard X-ray (14-195 keV) selected AGN outside the Galactic plane having measured spectroscopic redshifts and BH mass estimates (respectively 4. The first directly constrained BHMF and ERDF using both unobscured and obscured AGN, in addition to a highly robust determination of the XLF (Ananna et al 2022).…”

“…Additionally, despite sufficient spectral resolution to resolve the velocity dispersions associated with the bulges of relatively small SMBHs (∼ 10 4 − 10 5 𝑀 ), we do not find a significant population of such AGN, which (given the BAT flux limit) would have presented super-Eddington accretion rates. Ananna et al (2022) use the highly complete set of BASS DR2 measurements to derive the intrinsic XLF, BH mass function (BHMF) and Eddington ratio distribution function (ERDF), for both obscured and unobscured low-redshift AGN using the BAT sample. It employs an elaborate forward-modeling approach to derive the intrinsic XLF, BHMF and BHMF from the observed distributions, while accounting for various selection effects.…”

“…In this section, we briefly illustrate the distributions of some of the key AGN-related properties of the BAT 70-month AGN, as determined through the BASS DR2 measurements We also briefly discuss the reliability and limitations of the measurements. A more elaborate forward-modeling approach accounting for various survey selection effects associated with a flux-limited survey with various levels of obscuration is described in Ananna et al (2022).…”

BASS XXVI: DR2 Host Galaxy Stellar Velocity Dispersions

“…Broad emission line measurements for the BASS DR2 sample are presented in Mejía-Restrepo et al (2022), while narrow-line measurements are presented in Oh et al (2022). Ananna et al (2022) uses the highly complete set of BASS DR2 measurements to derive the intrinsic X-ray luminosity function (XLF), black hole mass function (BHMF) and Eddington ratio distribution function (ERDF), for both obscured and unobscured low-redshift AGN, relying on the 𝜎 * measurements presented here (for narrow-line systems). Completing the DR2 Special Issue, the details of the DR2 near-infrared (NIR) spectroscopy are provided in Brok et al (2022), with an investigation of NIR coronal lines.…”