Circumnuclear regions of different BPT types in star-forming MaNGA
  galaxies: AGN detectability
  We consider the circumnuclear regions of MaNGA galaxies. The spectra are
classified as AGN-like, HII-region-like (or SF-like), and intermediate (INT)
spectra according to their positions on the BPT diagram. There are the
following four configurations of the radiation distributions in the
circumnuclear regions: 1) AGN+INT, the innermost region of the AGN-like
radiation is surrounded by a ring of radiation of the intermediate type; 2)
INT, the central area of radiation of the intermediate type; 3) SF+INT, the
inner region of the HII-region-like radiation is surrounded by a ring of
radiation of the intermediate type; and 4) SF, the HII-region-like radiation
only. The LINERS of configurations 1 and 2 are examined. The spaxel spectra of
the LINERs form a sequences on the BPT diagram. The line ratios change smoothly
with radius, from AGN-like at the center to HII-region-like at larger
distances. This is in agreement with the paradigm that the LINERs are excited
by AGN activity. The AGN and INT radiation in the circumnuclear region is
accompanied by an enhanced gas velocity dispersion, s_g. The radius of the area
of the AGN and INT radiation is similar to the radius of the area with enhanced
s_g, and the central s_g,c correlates with the luminosity of the AGN+INT area.
We assume that the gas velocity dispersion can serve as an indicator of the AGN
activity. The values of s_g,c for the SF-type centers partly overlap with those
of the AGN-type centers. We find that there is a demarcation line between the
positions of the AGN-type and SF-type objects on the s_g,c - central Halpha
surface brightness diagram.
