发表机构
Kavli Institute for Particle Astrophysics & Cosmology, Stanford University; Center for Decoding the Universe, Stanford University; Racah Institute of Physics, The Hebrew University of Jerusalem; Universität Heidelberg, Zentrum für Astronomie, Astronomisches Rechen-Institut; Observatories of the Carnegie Institution for Science; Department of Astronomy & Astrophysics, University of California, San Diego; Department of Astronomy and Joint Space-Science Institute, University of Maryland, College Park; Departamento de Astronomía, Universidad de Chile; Max-Planck-Instit（斯坦福大学卡弗里粒子天体物理与宇宙学研究所; 斯坦福大学解码宇宙中心; 耶路撒冷希伯来大学拉卡物理学研究所; 海德堡大学天文中心计算天文研究所; 卡内基科学学会天文台; 加州大学圣地亚哥分校天文学与天体物理学系; 马里兰大学学院公园分校天文学系与联合空间科学研究所; 智利大学天文学系; 马克斯·普朗克研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用PHANGS-MUSE观测，通过建模电离光子泄漏与光谱硬化，揭示了HII区与弥散电离气体的辐射耦合机制，解释了线比序列及其对恒星形成率的依赖。
AI 中文摘要
恒星形成星系的光学发射线比在光致电离框架下已被广泛理解，但仍有一些系统性趋势未得到解释。利用PHANGS-MUSE对19个近邻星系的50-100 pc分辨率观测，我们研究了逃逸的电离辐射如何将HII区与弥散电离气体（DIG）耦合起来，分析了数千个HII区和DIG视线。HII区和DIG在标准线比诊断图（如BPT图）上形成连续序列，其中逐渐变暗的区域显示出升高的高电离和低电离线比，而DIG将相同的趋势延伸到复合-LINER区域。线比随全球恒星形成率（sSFR）的变化表明，随着恒星形成活动的增强，电离辐射逐渐变硬，这与发射越来越由老年恒星族群主导的预期相反。视线混合解释了部分行为，但无法重现所有线比趋势。因此，我们开发了一个模型，其中电离光子从HII区逃逸并穿过弥散星际介质，经历几何稀释、衰减和光谱硬化。该模型预测，逐渐变暗的HII区越来越多地由来自邻近明亮区域的泄漏辐射电离，这意味着HII区之间存在辐射耦合。对HII区和DIG的联合建模重现了逃逸分数约为0.4-0.6和电离光子平均自由程约为0.5-1 kpc时的HII区光度分布和DIG表面亮度，并定性地重现了观测到的线比序列及其对sSFR的依赖性。我们的结果表明，电离光子泄漏可能提供了一个重要的非局部反馈通道，将紧凑的恒星形成区域与大规模星系盘联系起来。
英文摘要
The optical emission-line ratios of star-forming galaxies are broadly understood in the framework of photoionization, yet some systematic trends remain unexplained. Using 50--100 pc resolution PHANGS-MUSE observations of 19 nearby galaxies, we investigate how escaping ionizing radiation couples HII regions to the diffuse ionized gas (DIG), analyzing thousands of HII regions and DIG sightlines. HII regions and the DIG form a continuous sequence across standard line-ratio diagnostic diagrams (e.g., BPT diagrams), where progressively fainter regions show elevated high- and low-ionization line ratios, and the DIG extends the same trends into the composite--LINER regime. Line-ratio variations with global specific star formation rate (sSFR) suggest progressively harder ionizing radiation with increasing star formation activity, contrary to expectations for emission increasingly dominated by older stellar populations. Line-of-sight mixing explains part of the behavior but cannot reproduce all line-ratio trends. We therefore develop a model in which ionizing photons escape HII regions and propagate through the diffuse ISM, undergoing geometric dilution, attenuation, and spectral hardening. The model predicts that progressively fainter HII regions are increasingly ionized by leaked radiation from neighboring luminous regions, implying radiative coupling between HII regions. Joint modeling of HII regions and the DIG reproduces the HII region luminosity distribution and DIG surface brightness for escape fractions of $\sim$0.4$-$0.6 and ionizing-photon mean free paths of $\sim$0.5$-$1 kpc, and qualitatively reproduces the observed line-ratio sequences and their dependence on sSFR. Our results suggest that ionizing photon leakage may provide an important non-local feedback channel linking compact star-forming sites to large-scale galaxy disks.
CommentsSubmitted to ApJ. Comments are welcome!
