THE GLOBAL RATE AND EFFICIENCY OF STAR-FORMATION IN SPIRAL GALAXIES AS A FUNCTION OF MORPHOLOGY AND ENVIRONMENT

CCD images of H alpha and R-band emission in 120 spiral galaxies were obtained using the now-retired No. 1-0.9 m telescope of Kitt Peak Nati onal Observatory. These images were used to derive the distribution an d total flux of continuum-subtracted Ha line emission, and therefore t he H alpha surface brightnesses and high mass star formation rates in these galaxies. We find a small but significant variation in the mean H alpha surface brightness for spiral galaxies along the Hubble sequen ce; the Sd-Ir galaxies exhibit a mean H alpha surface brightness 1.4 t imes higher than the Sbc-Scd galaxies, and 2-3 times higher than the S a-Sb galaxies. Estimates for the total formation rate for high mass st ars have been compared with global molecular gas masses to determine t he global efficiency of high mass star formation (=L/M(gas)) as a fun ction of morphological type and environment. We find that the mean eff iciency of high mass star formation in this sample of spiral galaxies shows little dependence on morphological type for galaxies of type Sa through Scd, although there is a wide range in star formation efficien cies within each type. Galaxies in disturbed environments (i.e., stron gly interacting systems) are found to have a mean star formation effic iency similar to 4 times higher than in isolated spiral galaxies, unco rrected for extinction. This confirms previous findings (Young et al. 1986a,b; Sanders er al. 1986; Solomon & Sage 1988; Tinney ct al. 1990) , based on the far-infrared luminosity rather than the H alpha luminos ity to trace the rate of high mass star formation, that the mean star formation efficiency among isolated galaxies is significantly lower th an that among interacting systems. This result provides further confir mation that the rate of high mass star formation is reasonably well tr aced by both the H alpha and the IR luminosity in spiral galaxies. (C) 1996 American Astronomical Society.