Morphology of AGN Emission Line Regions in SDSS-IV MaNGA Survey
  Extended narrow-line regions (NLRs) around active galactic nuclei (AGN) are
shaped by the distribution of gas in the host galaxy and by the geometry of the
circumnuclear obscuration, and thus they can be used to test the AGN
unification model. In this work, we quantify the morphologies of the
narrow-line regions in 308 nearby AGNs ($z=0-0.14$, \lbol $\sim 10^{42.4-44.1}$
\erg{}) from the MaNGA survey. Based on the narrow-line region maps, we find
that a large fraction (81\%) of these AGN have bi-conical NLR morphology. The
distribution of their measured opening angles suggests that the intrinsic
opening angles of the ionization cones has a mean value of 85--98$^\circ$ with
a finite spread of 39-44$^\circ$ (1-$\sigma$). Our inferred opening angle
distribution implies a number ratio of type I to type II AGN of 1:1.6--2.3,
consistent with other measurements of the type I / type II ratio at low AGN
luminosities. Combining these measurements with the WISE photometry data, we
find that redder mid-IR color (lower effective temperature of dust) corresponds
to stronger and narrower photo-ionized bicones. This relation is in agreement
with the unification model that suggests that the bi-conical narrow-line
regions are shaped by a toroidal dusty structure within a few pc from the AGN.
Furthermore, we find a significant alignment between the minor axis of host
galaxy disks and AGN ionization cones. Together, these findings suggest that
obscuration on both circumnuclear ($\sim $pc) and galactic ($\sim$ kpc) scales
are important in shaping and orienting the AGN narrow-line regions.
