BASS XXIV: The BASS DR2 Spectroscopic Line Measurements and AGN
  Demographics
  We present the second catalog and data release of optical spectral line
measurements and AGN demographics of the BAT AGN Spectroscopic Survey, which
focuses on the of Swift-BAT hard X-ray detected AGNs. We use spectra from
dedicated campaigns and publicly available archives to investigate spectral
properties of most of the AGNs listed in the 70-month Swift-BAT all-sky
catalog; specifically, 743 of the 746 unbeamed and unlensed AGNs (99.6%). We
find a good correspondence between the optical emission line widths and the
hydrogen column density distributions using the X-ray spectra, with a clear
dichotomy of AGN types for NH = 10^22 cm-2. Based on optical emission-line
diagnostics, we show that 48%-75% of BAT AGNs are classified as Seyfert,
depending on the choice of emission lines used in the diagnostics. The fraction
of objects with upper limits on line emission varies from 6% to 20%. Roughly 4%
of the BAT AGNs have lines too weak to be placed on the most commonly used
diagnostic diagram, [O III]{\lambda}5007/H\b{eta} versus [N
II]{\lambda}6584/H{\alpha}, despite the high signal-to-noise ratio (S/N) of
their spectra. This value increases to 35% in the [O III]{\lambda}5007/[O
II]{\lambda}3727 diagram, owing to difficulties in line detection. Compared to
optically-selected narrow-line AGNs in the Sloan Digital Sky Survey, the BAT
narrow-line AGNs have a higher rate of reddening/extinction, with
H{\alpha}/H\b{eta} > 5 (~ 36%), indicating that hard X-ray selection more
effectively detects obscured AGNs from the underlying AGN population. Finally,
we present a subpopulation of AGNs that feature complex broad-lines (34%,
250/743) or double-peaked narrow emission lines (2%, 17/743).
