Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639
Abstract
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 ∼ {10}6 {M}⊙ and an ionization rate of 6.4× {10}51 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 {10}4 {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 ≥slant 5.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2016
- DOI:
- 10.3847/0004-637X/825/2/145
- arXiv:
- arXiv:1605.02822
- Bibcode:
- 2016ApJ...825..145E
- Keywords:
-
- galaxies: dwarf;
- galaxies: individual: Kiso 5639;
- galaxies: photometry;
- galaxies: star clusters: general;
- galaxies: star formation;
- H II regions;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, 14 figures, 3 tables, accepted by ApJ