2015MNRAS.446.4291L

We present new narrow-band (Hα and [O iii]) images 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/s2. 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 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 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, which is ∼ 1/5 of our Milky Way's. Based on the analysis results for young stellar clusters in the HII region, the bright HII 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 HII region is still uncertain.