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We examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular(dIrr) and Blue Compact Dwarf (BCD) galaxies to identify distinct young regionsin their far outer disks. We use these data, obtained with the Galaxy EvolutionExplorer satellite, to determine the furthest radius at which in situ starformation can currently be identified. The FUV knots are found at distancesfrom the center of the galaxies of 1 to 8 disk scale lengths and have ages of<20 Myrs and masses of 20 to 1E5 Msolar. The presence of young clusters and OBassociations in the outer disks of dwarf galaxies shows that dIrrs do have starformation taking place there in spite of the extreme nature of the environment.Most regions are found where the HI surface density is ~1 Msolar per pc2,although both the HI and dispersed old stars go out much further. This limitingdensity suggests a cutoff in the ability to form distinct OB associations andperhaps even stars. We compare the star formation rates in the FUV regions tothe average rates expected at their radii and beyond from the observed gas,using the conventional correlation for gas-rich regions. The localized ratesare typically 10% of the expected average rates for the outer disks. Eitherstar formation in dIrrs at surface densities <1 Msolar per pc2 occurs withoutforming distinct associations, or the Kennicutt-Schmidt relation over-predictsthe rate beyond this point. In the latter case, the stellar disks in thefar-outer parts of dIrrs result from scattering of stars from the inner disk.

Young star clusters in the outer disks of LITTLE THINGS dwarf irregular galaxies