AST-98-70112 Bruce Elmegreen Irregular galaxies are the most common type of galaxy in the Universe. Because they have evolved relatively slowly over time, they chemically resemble the outer parts of present day spirals and young galaxies seen at large look-back times. Unlike spirals, however, irregulars have no density waves and less shear in their interstellar media. Yet, most irregulars have on-going star formation. Therefore, non-interacting irregular galaxies give us the opportunity to examine processes of star formation in the absence of spiral density waves and external perturbations. These processes may play an important role in spiral galaxies too, but there they are masked by the consequences of the density wave. Dr. Elmegreen is collaborating with Dr. Hunter to answer the question: What regulates the star formation activity in irregular galaxies on global and local scales? They are proceeding (1) to quantify the nature and distribution of the star formation activity, (2) to characterize the interstellar medium out of which clouds and stars form, and (3) to combine the observations with models to develop a realistic picture for the onset of star formation in these systems. The observations probe star formation on three timescales: H a images trace the most recent star formation, UBV images integrate the star formation over the past Gyr, and JHK images integrate the star formation over the lifetime of the galaxy. To characterize the interstellar medium, the team is using radio interferometer maps of HI line emission and absorption. ***
