JWST is producing high-quality rest-frame optical and UV spectra of faint galaxies at z > 4 for the first time, challenging models of galaxy and stellar populations. One galaxy recently observed at z = 5.943, GS9422, has nebular line and UV continuum emission that appears to require a high ionizing photon production efficiency. This has been explained with an exotic stellar initial mass function (IMF; Cameron et al. 2023a), 10–30x more top-heavy than a Salpeter IMF. Here we suggest an alternate explanation to this exotic IMF. We use a new flexible neural net emulator for CLOUDY, Cue, to infer the shape of the ionizing spectrum directly from the observed emission line fluxes. By describing the ionizing spectrum with a piecewise power law, Cue is agnostic to the source of the ionizing photons. Cue finds that the ionizing radiation from GS9422 can be approximated by a double power law characterized by QHeIIQH=−1.5 , which can be interpreted as a combination of young, metal-poor stars and a low-luminosity active galactic nucleus with F _ν ∝ λ ² in a 65%/35% ratio. This suggests a significantly lower nebular continuum contribution to the observed UV flux (24%) than a top-heavy IMF (≳80%), and hence, necessitates a damped Lyα absorber to explain the continuum turnover bluewards of ∼1400 Å. While current data cannot rule out either scenario, given the immense impact the proposed top-heavy IMF would have on models of galaxy formation, it is important to propose viable alternative explanations and to further investigate the nature of peculiar high-z nebular emitters.

中文翻译：

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不需要头重脚轻的恒星初始质量函数：GS9422 的电离辐射可以由活跃星系核和恒星的混合物提供动力


JWST 首次生成 z > 4 微弱星系的高质量静止框架光学和紫外光谱，对星系和恒星群模型提出了挑战。最近在 z = 5.943 观测到的一个星系 GS9422 具有星云线和紫外连续发射，似乎需要高电离光子产生效率。这可以用奇异的恒星初始质量函数（IMF；Cameron et al. 2023a）来解释，它比 Salpeter IMF 的头重脚轻 10-30 倍。在这里，我们对这个奇异的国际货币基金组织提出了另一种解释。我们使用 CLOUDY 的新型灵活神经网络模拟器 Cue，直接从观察到的发射线通量推断电离谱的形状。通过用分段幂律描述电离谱，Cue 对电离光子的来源是不可知的。 Cue 发现来自 GS9422 的电离辐射可以通过以 QHeIIQH=−1.5 为特征的双幂律来近似，这可以解释为年轻、贫金属恒星和 F _ν ∝ λ ² 比例为 65%/35%。这表明星云连续谱对观测到的紫外通量 (24%) 的贡献明显低于头重脚轻的 IMF (≳80%)，因此需要阻尼 Lyα 吸收器来解释~1400 Å 的连续谱向蓝周转。虽然目前的数据不能排除这两种情况，但考虑到所提出的头重脚轻的 IMF 对星系形成模型的巨大影响，提出可行的替代解释并进一步研究特殊的高 z 星云发射体的性质非常重要。