Do Density Waves Trigger Star Formation?

A comparison of B - V colors, blue and far-IR surface brightnesses, metallicities, and star formation rates calculated from H-alpha and UV fluxes reveals no difference in the average star formation rates for galaxies with and without grand design spiral structure. This implies that strong density waves do not trigger a significant excess of star formation compared to that in similar galaxies without a wave. Density waves organize the gas and young stars into spiral arms because of the flow pattern, and they may influence the formation and destruction of the largest cloud complexes, but they appear to contribute less than 50 percent to the overall star formation rate.