Next Contents


This contribution presents an observational overview of the influence of bars on star formation and nonstellar activity in the centers of nearby spiral galaxies. The non-axisymmetric gravitational perturbation of a large-scale stellar bar or oval distortion in a spiral disk is an effective mechanism for inducing radial inflow of gas toward the center of a galaxy. As a consequence of shocks and cloud-cloud collisions, gas piles up along the leading edges of the stellar bar (Roberts, Huntley, & van Albada 1979). The resulting asymmetric distribution of the gas with respect to that of the stars causes the latter to exert a gravitational torque on the former, thereby driving the gas inward. If the galaxy has inner Lindblad resonances (ILRs), the gas will collect between the inner and outer ILRs in the form of a ring-like configuration (see, e.g., Athanassoula 1992). This is an attractive way to supply gas to sustain the star formation activity observed in the central few hundred parsecs of many galaxies, since gravitational instability leading to cloud collapse may be an inevitable consequence of the accumulation of large amounts of neutral gas (Elmegreen 1994). Further inflow to smaller scales might proceed by a variety of pathways (e.g., Heller & Shlosman 1994; Wada & Habe 1992), although the detailed processes involved have yet to be thoroughly understood (Phinney 1994; Begelman 1994). Nevertheless, bar-driven inflow as a mechanism for the fueling of active galactic nuclei (AGNs) has been a popular idea (e.g., Simkin, Su, & Schwarz 1980; Shlosman, Frank, & Begelman 1989; Friedli & Benz 1993; Heller & Shlosman 1994).