Abstract
We present measurements of broad emission lines and virial estimates of
supermassive black hole masses ($M_BH$) for a large sample of ultra-hard
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 689 AGNs, determined from the H$\alpha$, H$\beta$,
$MgIIłambda2798$, and/or $CIVłambda1549$ 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 H$\alpha$ emission lines in obscured AGNs ($(N_\rm
H/cm^-2)> 22.0$) are on average a factor of $8.0_-2.4^+4.1$
weaker, relative to ultra-hard X-ray emission, and about $35_-12^~+7$\%
narrower than in unobscured sources (i.e., $(N_H/cm^-2) <
21.5$). 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 ($>$1 dex) masses for Type 1.9
sources (AGNs with broad H$\alpha$ but no broad H$\beta$) and/or sources with
$(N_H/cm^-2) > 22.0$. We provide simple multiplicative
corrections for the observed luminosity and width of the broad H$\alpha$
component ($LbH\alpha$ and FWHMbH$\alpha$) in such sources to
account for this effect, and to (partially) remedy $M_BH$ estimates for Type
1.9 objects. As key ingredient of BASS/DR2, our work provides the community
with the data needed to further study powerful AGNs in the low-redshift
Universe.
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