  Massive molecular clouds have been discovered in massive elliptical galaxies
at the center of galaxy clusters. Some of this cold gas is expected to flow in
the central supermassive black holes and activate galactic nucleus (AGN)
feedback. In this study, we analyze archival ALMA data of 9 massive elliptical
galaxies, focusing on CO line emissions, to explore the circumnuclear gas. We
show that the mass of the molecular gas within a fixed radius (500 pc) from the
AGNs (M_mol ~ 10^7-10^8 M_sun) is correlated with the jet power estimated from
X-ray cavities (P_cav ~ 10^42-10^45 erg/s). The mass accretion rate of the
circumnuclear gas \dot{M} also has a correlation with P_cav. On the other hand,
the continuum luminosities at ~1.4 GHz and ~100-300 GHz have no correlation
with M_mol. These results indicate that the circumnuclear gas is sustaining the
long-term AGN activities (~10^7 yr) rather than the current ones. The
circumnuclear gas mass is a better indicator of the jet power than the
continuum luminosity, which probably changes on a shorter time scale. We also
study the origin of the continuum emission from the AGNs at ~100-300 GHz and
find that it is mostly synchrotron radiation. For low-luminosity AGNs, however,
dust emission appears to contaminate the continuum.
