The HI dominated Low Surface Brightness Galaxy KKR17

Original · EN

We present new narrow-band (Hα and [OIII]) imagings and optical spectrophotometry of HII regions for a gas-rich low surface brightness irregular galaxy, KKR 17. The central surface brightness of the galaxy is μ₀(B) = 24.15 ±0.03 mag sec⁻². The galaxy was detected by Arecibo Legacy Fast ALFA survey (ALFALFA), and its mass is dominated by neutral hydrogen (HI) gas. In contrast, both the stellar masses of the bright HII and diffuse stellar regions are small. In addition, the fit to the spectral energy distribution to each region shows the stellar populations of HII and diffuse regions are different. The bright HII region contains a large fraction of O-type stars, revealing the recent strong star formation, whereas the diffuse region is dominated by median age stars, which has a typical age of 600 Myrs. Using the 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, which is 1/5 of our Milky Way's. Based on the analysis results to young stellar clusters in HII region, it is found that the bright HII region showed two sub-components with different velocities and metallicities. This may be caused by the outflow of massive stars or merging events. However, the mechanism of triggering star formation in the HII region is still uncertain.