Discovery of an Outstanding Disk in the cD Galaxy of the Hydra A Cluster
  The central cD galaxy of the Hydra A cluster has one of the most powerful
active galactic nuclei (AGNs) in the nearby Universe (z <0.2). We report on the
discovery of a dust lane in the cD galaxy using Subaru telescope. The i'-band
image shows the existence of a dark band of the size of 3.6"x 0.7" (4 kpc x 0.8
kpc), which appears to be quite similar to the dust lane observed in Centaurus
A. The morphology indicates that the cold disk that seen as the dust lane is
almost edge-on and rotates around the AGN. Since the minor axis of the dust
lane is nearly parallel to the radio jets emerging from the AGN, the disk is
probably feeding its gas into the central black hole. From the absorption, we
estimate the hydrogen column density of the lane is N_H=2.0 x 10^21 cm^-2, and
the mass of the disk is ~8 x 10^7 M_sun. The column density is consistent with
constraints obtained from Chandra X-ray observations. The age of the disk is >~
4 x 10^7 yr. The position angle of the disk and the galaxy's photometric axis
are misaligned, which may imply that the cold gas in the disk is brought via
galaxy mergers. Our observations may indicate that the supply of cold gas by
galaxy mergers is required for the most intensive feedback from AGNs.
