Hydrogen recombination near-infrared line mapping of Centaurus A with
  IRSF/SIRIUS
  Centaurus A (Cen A) is one of the most famous galaxies hosting an active
galactic nucleus (AGN), where the interaction between AGN activities and
surrounding interstellar and intergalactic media has been investigated. Recent
studies reported detections of the H{\alpha} emission from clouds in the
galactic halo toward the northeast and southwest of the nucleus of Cen A,
suggesting that AGN jets may have triggered star formation there. We performed
near-infrared line mapping of Cen A with the IRSF 1.4-m telescope, using the
narrow-band filter tuned for Pa{\beta}, from which we find that the Pa{\beta}
emission is not detected significantly from either northeast or southwest
regions. The upper limit of the Pa{\beta}/H{\alpha} ratio in the northeast
region is compatible with that expected for a typical HII region, in line with
the scenario that AGNs have triggered star formation there. On the other hand,
the upper limit of Pa{\beta}/H{\alpha} in the southwest region is significantly
lower than that expected for a typical HII region. A possibility to explain the
low Pa{\beta}/H{\alpha} ratio in the southwest region is the scattering of
H{\alpha} and Pa{\beta} photons from the center of Cen A by dust grains in the
halo clouds. From the upper limit of Pa{\beta}/H{\alpha} in the southwest
region, we obtain constraints on the dust size distribution, which is found to
be compatible with those seen in the interstellar medium of our Galaxy.
