YOUNG STAR CLUSTERS IN THE OUTER DISKS OF LITTLE THINGS DWARF IRREGULAR GALAXIES

Journal Article · Wed Jun 01 04:00:00 EDT 2016 · The Astronomical Journal (Online)

DOI:https://doi.org/10.3847/0004-6256/151/6/136· OSTI ID:22863160

Hunter, Deidre A.; Gehret, Elizabeth ^[1]; Elmegreen, Bruce G. ^[2]

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1. Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)
2. IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States)

We examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular (dIrr) and Blue Compact Dwarf galaxies to identify distinct young regions in their far outer disks. We use these data, obtained with the Galaxy Evolution Explorer satellite, to determine the furthest radius at which in situ star formation can currently be identified. The FUV knots are found at distances from the center of the galaxies of 1–8 disk scale lengths and have ages of ⩽20 Myr and masses of 20 M{sub ⊙} to 1 × 10{sup 5}M{sub ⊙}. The presence of young clusters and OB associations in the outer disks of dwarf galaxies shows that dIrrs do have star formation taking place there in spite of the extreme nature of the environment. Most regions are found where the H i surface density is ∼1 M{sub ⊙} pc{sup −2}, though both the H i and dispersed old stars go out much further. This limiting density suggests a cutoff in the ability to form distinct OB associations and perhaps even stars. We compare the star formation rates in the FUV regions to the average rates expected at their radii and beyond from the observed gas, using the conventional correlation for gas-rich regions. The localized rates are typically 10% of the expected average rates for the outer disks. Either star formation in dIrrs at surface densities <1 M{sub ⊙} pc{sup −2} occurs without forming distinct associations, or the Kennicutt–Schmidt relation over-predicts the rate beyond this point. In the latter case, the stellar disks in the far-outer parts of dIrrs result from scattering of stars from the inner disk.

• OSTI ID: 22863160
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 6 Vol. 151; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
CORRELATIONS
DENSITY
DISTANCE
EXPLORER SATELLITES
GALAXIES
MASS
SCATTERING
STAR CLUSTERS
STARS