Unobscured Type 2 AGNs
  Type 2 AGNs with intrinsically weak broad emission lines (BELs) would be
exceptions to the unified model. After examining a number of proposed
candidates critically, we find that the sample is contaminated significantly by
objects with BELs of strengths indicating that they actually contain
intermediate-type AGNs, plus a few Compton-thick sources as revealed by
extremely low ratios of X-ray to nuclear IR luminosities. We develop
quantitative metrics that show two (NGC 3147 and NGC 4594) of the remaining
candidates to have BELs 2-3 orders of magnitude weaker than those of typical
type-1 AGNs. Several more galaxies remain as candidates to have anomalously
weak BELs, but this status cannot be confirmed with the existing information.
Although the parent sample is poorly defined, the two confirmed objects are
well under 1% of its total number of members, showing that the absence of a BEL
is possible, but very uncommon in AGN. We evaluate these two objects in detail
using multi-wavelength measurements. They have little X-ray extinction with N_H
< 10^21 cm^{-2}. Their IR spectra show strong silicate emission (NGC 4594) or
weak aromatic features on a generally power law continuum with a suggestion of
silicates in emission (NGC 3147). No polarized BEL is detected in NGC 3147.
These results indicate that the two unobscured type-2 objects have
circumnuclear tori that are approximately face-on. Combined with their X-ray
and optical/UV properties, this behavior implies that we have an unobscured
view of the nuclei and thus that they have intrinsically weak BELs. We compare
their properties with those of the other less-extreme candidates. We then
compare the distributions of bolometric luminosities and accretion rates of
these objects with theoretical models that predict weak BELs.
