Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639
Publication date: 14 July 2016
Authors: Elmegreen, D., et al.
Journal: The Astrophysical Journal
Copyright: © 2016. The American Astronomical Society
The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ~106 M⊙ and an ionization rate of 6.4 × 1051 s−1, equivalent to ~2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ~1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of −1.73 ± 0.51. Fourteen young clusters in the head are more massive than 104 M⊙, suggesting a clustering fraction of 30%–45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H II region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H II region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ~3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt–Schmidt rate by a factor of ≥5.Link to publication