Searching for Star Formation in the Outer Disks of Dwarf Galaxies

The outer disks of dwarf galaxies provide an extreme environment for studies of star formation because of their low gas densities and metallicities. Previous work has found evidence of young star clusters in the outer disks of dwarf galaxies, but it is unclear how these star clusters could have formed there since the gas density is too low to fragment into clouds via gravitational instability. We searched for young star clusters in the outer disks of dwarf galaxies with new deep images of three dwarf galaxies in four filters from the Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey (LITTLE THINGS). We confirmed one young star cluster in the outer disk of DDO 43, which also appeared in Hα and far ultraviolet images. We found three additional young star cluster candidates, one in the outer disk of DDO 43 and two in the outer disk of DDO 187. We use photometry of the young star cluster and cluster candidates and a model catalog of cluster evolution to estimate the age and mass and measure diameters of the star clusters. We found that the confirmed young star cluster and the candidate cluster in DDO 43 have reasonable masses and diameters but the two cluster candidates in DDO 187 are very small. Our findings suggest that it is possible for stars to form in the outer disks of dwarf galaxies. This research has been supported by NSF awards 1852478 and 1950901 to Northern Arizona University for the 2020 REU program.