Circumnuclear Medium around the Central AGN in a Cool-Core Cluster,
  Abell 1644-South
  We present the circumnuclear multi-phase gas properties of the brightest
cluster galaxy (BCG) in the center of Abell 1644-South. A1644-S is the main
cluster in a merging system, which is well known for X-ray hot gas sloshing in
its core. The sharply peaked X-ray profile of A1644-S implies the presence of a
strongly cooling gas core. In this study, we analyze ALMA CO (1-0) data, JVLA
HI data, and KaVA 22 GHz data for the central region of A1644-S to probe the
potential origin of the cool gas and its role in (re)powering the central
active galactic nucleus (AGN). We find CO clumps distributed in an arc shape
along the X-ray gas sloshing, which is suggestive of a connection between the
cold gas and the hot intracluster medium (ICM). HI and CN are detected in
absorption against the AGN continuum emission. The absorption dip is observed
at the systemic velocity of the BCG with an extended, redshifted tail. Based on
the spatial and spectral configurations of the HI, CN and CO gases, it is
inferred that cool gas spirals into the core of the BCG, which is then fed to
the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar
jet, implying that this AGN could have been (re)powered quite recently.
Combining this, we suggest that some cold gas in A1644-S could have been formed
from the cooling of the ICM, triggering the activity of the central AGN in the
early development of a cool-core cluster.
