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

Julian E. Mejía-Restrepo*, Benny Trakhtenbrot, Michael J. Koss, Kyuseok Oh, Jakob Den Brok, Daniel Stern, Meredith C. Powell, Federica Ricci, Turgay Caglar, Claudio Ricci, Franz E. Bauer, Ezequiel Treister, Fiona A. Harrison, C. M. Urry, Tonima Tasnim Ananna, Daniel Asmus, Roberto J. Assef, Rudolf E. Bär, Patricia S. Bessiere, Leonard BurtscherKohei Ichikawa, Darshan Kakkad, Nikita Kamraj, Richard Mushotzky, George C. Privon, Alejandra F. Rojas, Eleonora Sani, Kevin Schawinski, Sylvain Veilleux

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We present measurements of broad emission lines and virial estimates of supermassive black hole masses (M BH) for a large sample of ultrahard X-ray-selected active galactic nuclei (AGNs) as part of the second data release of the BAT AGN Spectroscopic Survey (BASS/DR2). Our catalog includes M BH estimates for a total of 689 AGNs, determined from the Hα, Hβ, Mg ii λ2798, and/or C iv λ1549 broad emission lines. The core sample includes a total of 512 AGNs drawn from the 70 month Swift/BAT all-sky catalog. We also provide measurements for 177 additional AGNs that are drawn from deeper Swift/BAT survey data. We study the links between M BH estimates and line-of-sight obscuration measured from X-ray spectral analysis. We find that broad Hα emission lines in obscured AGNs ( log(NH/cm-2)>22.0 ) are on average a factor of 8.0-2.4+4.1 weaker relative to ultrahard X-ray emission and about 35-12+7 % narrower than those in unobscured sources (i.e., log(NH/cm-2)<21.5 ). This indicates that the innermost part of the broad-line region is preferentially absorbed. Consequently, current single-epoch M BH prescriptions result in severely underestimated (>1 dex) masses for Type 1.9 sources (AGNs with broad Hα but no broad Hβ) and/or sources with log(NH/cm-2)≳22.0 . We provide simple multiplicative corrections for the observed luminosity and width of the broad Hα component (L[bHα] and FWHM[bHα]) in such sources to account for this effect and to (partially) remedy M BH estimates for Type 1.9 objects. As a key ingredient of BASS/DR2, our work provides the community with the data needed to further study powerful AGNs in the low-redshift universe.

Original languageEnglish
Article number5
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - 1 Jul 2022


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