Published online by Cambridge University Press: 25 May 2016
It is now widely accepted that a combination of torques and dissipation can drive molecular gas into the circumnuclear (inner kpc) region of spirals. However, the fate of the circumnuclear gas is poorly understood and depends on inflow mechanisms, outflow processes, and on star formation. It is unclear why spiral galaxies convert comparable amount of circumnuclear H2 into stars over a timescale (tsf) that varies by nearly two orders of magnitude between galaxies. The ratio M(H2)/L(RC) can be used to show the range in this timescale, where L(RC) is the 1.49 GHz radio continuum (RC) luminosity (Condon et al. 1990), and M(H2) the hydrogen mass traced by CO observations in the central 45″ (4.5 kpc for D=20 Mpc). A similar range is seen if the central 10 micron luminosity is used. Preliminary results from Jogee's thesis suggest that the circumnuclear gas consumption timescale by star formation (tsf) is correlated with the gas morphology (see Fig. 1) and kinematics. In particular, the value of tsf spans a large range in different kinematic regimes within a given galaxy, and together with inflow, this can lead some galaxies to follow evolutionary paths sketched in Fig. 1.