Cold gas contents of galaxies and its relation to fueling: Gas dynamics and related phenomena in bar-driven evolution of disk galaxies

The distribution and the dynamics of the cold gas in the circumnuclear regions (r ≲ [1 − a few] kpc) of disk galaxies have been observed at high resolutions of a few arcsec in λ2.6 mm CO (J=1→0) line emission. Distinct CO features are commonly found in the observed disk galaxies and they are different from galaxy to galaxy. They are explained by means of orbit-resonance theories and dynamical evolution. The evolutionary sequence in time is constructed based on the studies of dynamics in theoretical works and numerical simulations in the literature. Not only the behavior of the cold gas but also the starburst, outbreaks of the active galactic nucleus, and the evolution of global structures in disk galaxies are discussed in the bar-driven evolution scenario.