Galaxy bars can be important triggering agents for star formation, radial gas flows, and nuclear activity. This paper reviews the observational evidence for bar-induced star formation and gas redistribution in spiral galaxies. Specific topics include the global star formation rates in barred vs normal galaxies, the spatial distribution and abundances of star forming regions in barred systems, and circumnuclear hotspots.
Barred galaxies present one of the clearest cases of mass-transfer induced activity, and as such are valuable laboratories for understanding the triggering of starbursts and nuclear activity in a broader context. As reviewed by Athanassoula elsewhere in this volume, hydrodynamic simulations suggest that bars can trigger a wide range of phenomena, including large-scale gas compression, star formation, and radial transport of gas into the nuclear region (also see Sellwood and Wilkinson 1993).
This paper reviews the observational evidence for bar-induced star formation and circumnuclear activity. I begin by discussing the integrated properties of barred vs normal spirals, based on surveys in Hα, radio continuum, and the infrared (section 2). Section 3 summarizes the star formation properties of individual barred systems, with emphasis on the bars themselves and their surrounding disks. In section 4 I discuss the circumnuclear “hotspot” star formation regions, which are probably the most distinctive signatures of bar-induced activity. I conclude with a summary of outstanding questions and important areas for future work.
INTEGRATED PROPERTIES OF BARRED VS NORMAL SPIRALS
The first systematic comparisons of the global properties of barred and normal galaxies were based on radio continuum surveys (Cameron 1971; Dressel and Condon 1978; Dressel 1979; Heckman 1980).