With a metallicity of 12 + Log(O/H) ≈ 7.1–7.2, I Zw 18 is a canonical low-metallicity blue compact dwarf (BCD) galaxy. A growing number of BCDs, including I Zw 18, have been found to host strong, narrow-lined, nebular He ii (λ4686) emission with enhanced intensities compared to Hβ (e.g., He ii(λ4686)/Hβ > 1%). We present new observations of I Zw 18 using the Keck Cosmic Web Imager. These observations reveal two nebular He ii emission regions (or He iii regions) northwest and southeast of the He iii region in the galaxy’s main body investigated in previous studies. All regions exhibit He ii(λ4686)/Hβ greater than 2%. The two newly resolved He iii regions lie along an axis that intercepts the position of I Zw 18's ultraluminous X-ray (ULX) source. We explore whether the ULX could power the two He iii regions via shock activity and/or beamed X-ray emission. We find no evidence of shocks from the gas kinematics. If the ULX powers the two regions, the X-ray emission would need to be beamed. Another potential explanation is that a class of early-type nitrogen-rich Wolf–Rayet stars with low winds could power the two He iii regions, in which case the alignment with the ULX would be coincidental.

I Zw 18 的金属丰度为 12 + Log(O/H) ≈ 7.1–7.2，是一个典型的低金属丰度蓝致密矮 (BCD) 星系。越来越多的 BCD，包括 I Zw 18，已被发现拥有强、窄线、星云 He ii ( λ 4686) 发射，与 H β（例如，He ii ( λ 4686)/H β > 1%）。我们使用 Keck Cosmic Web Imager 展示了对 I Zw 18 的新观测。这些观察露出两颗星云他II发射区（或他III地区），他的西北和东南III在以往的研究中星系的主体区域调查。所有地区都展示了 He ii( λ 4686)/H β大于 2%。两个新解析的 He iii区域位于一条轴上，该轴与 I Zw 18 的超亮 X 射线 (ULX) 源的位置相交。我们探索 ULX 是否可以通过冲击活动和/或 X 射线发射为两个 He iii区域供电。我们没有发现来自气体运动学的冲击的证据。如果 ULX 为这两个区域供电，则需要发射 X 射线。另一个可能的解释是，一类风速较低的早期型富氮沃尔夫-拉叶星可以为两个 He iii区域提供动力，在这种情况下，与 ULX 对齐将是巧合。