Outer Stellar and Gas Disks of Dwarf Galaxies

Outer edges of galaxies present an extreme environment for star formation. Dwarf irregular (dIm) galaxies already challenge models of star formation because of their low gas densities even in the central regions. Outer parts of dIm galaxies, therefore, present a particularly difficult test of our understanding of the cloud/star formation process. Yet, stars have formed even to extremely low levels of both gas and stellar surface densities. We have obtained ultra-deep broad-band images of 5 dIm galaxies, as well as HI maps, in order to explore the outer stellar disk and its relationship to the gas. To examine the role of the gas in determining the stellar disk, I include these galaxies with another 15 dwarfs and explore the relationship between how the gas falls with radius and the distribution of star formation activity, integrated star formation rates, and breaks in optical profiles. Recent star formation models provide motivation.