Publication Date:
2014-12-13
Description:
We present new narrow-band (Hα and [O iii ]) images and optical spectrophotometry of H ii regions for a gas-rich low-surface-brightness irregular galaxy, KKR 17. The central surface brightness of the galaxy is μ 0 ( B ) = 24.15 ± 0.03 mag s –2 . The galaxy was detected by the Arecibo Legacy Fast ALFA survey (ALFALFA). Its mass is dominated by neutral hydrogen (H i ) gas. In contrast, both the stellar masses of the bright H ii and diffuse stellar regions are small. In addition, the fit to the spectral energy distribution to each region shows the stellar populations of H ii and diffuse regions are different. The bright H ii region contains a large fraction of O-type stars, revealing recent strong star formation, whereas the diffuse region is dominated by median age stars with a typical age of ~600 Myr. Using McGaugh's abundance model, we found that the average metallicity of KKR 17 is 12 + (O/H) = 8.0 ± 0.1. The star-formation rate of KKR 17 is 0.21 ± 0.04 M yr –1 , which is ~1/5 of our Milky Way's. Based on the analysis results for young stellar clusters in the H ii region, the bright H ii region has two sub-components with different velocities and metallicities. This may be caused by the outflow of massive stars or merging events. However, the mechanism triggering star formation in the H ii region is still uncertain.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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