BAR-DRIVEN GAS STRUCTURE AND STAR-FORMATION IN THE CENTER OF M100

High-resolution (2.6 '' x2.4 '') CO(J=1-0) interferometry and near-infrared (J,H,K') imaging were made toward the Virgo spiral galaxy M100 (NGC 4321) to study gas kinematics and its relation to active phenomena in the center of a weakly barred disk galaxy. In the central 1 arcmin (5.0 kpc: D=17.1 Mpc) of M100, most of the molecular gas distributes within a similar to 3 kpc diameter region. In this region, there are prominent two-armed molecular spiral arms. The arms start at the ends of the nuclear stellar bar of similar to 16 '' (1.3 kpc) long seen in the near-infrared images. There is also a concentration of molecular gas with a diameter of similar to 3 '' (250 pc) at the dynamical center of the galaxy. Noncircular motion of the molecular gas is clearly seen and the deviation from circular motion is largest at the arms. From comparisons to theoretical models, we propose that the gas arms are formed through the orbit crowding of molecular clouds at the outer inner Lindblad resonance (OILR: r similar to 1 kpc), and the nuclear gas concentration is formed through infall of self-gravitating gas from the inner inner Lindblad resonance (IILR: r less than or similar to 0.7 kpc). The gaseous structure is driven by the nonaxisymmetric gravitational potential, which is mainly caused by the nuclear stellar bar in the central region. It is shown that analytical and numerical models based on the idea successfully reproduce the gaseous morphology and kinematics observed in the central region of M100. Massive star formation in the center of M100 is confined to the central 3 kpc gas distribution, and hotspots seen in H alpha are along the molecular spiral arms. Since the molecular spiral arms are the sites of orbit crowding and gas accumulation, cloud collisions, shocks, and gravitational instability are expected. The hotspots are probably attributed to these dynamical features at the OILR. The nuclear concentration of molecular gas induced also by the bar is a clear example of the bar-induced gas fueling to the nuclei of galaxies often suggested as a mechanism for feeding AGNs, though M100 does not show conspicuous AGN activity. (C) 1995 American Astronomical Society.