发表机构
University of Geneva; Université Paris-Saclay; Université Paris Cité; CEA; CNRS; AIM; National Radio Astronomy Observatory; George Mason University; Anton Pannekoek Institute for Astronomy, University of Amsterdam; Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine（日内瓦大学; 巴黎萨克雷大学; 巴黎西岱大学; 法国原子能和替代能源委员会; 法国国家科学研究中心; 天体物理、物质和辐射相互作用实验室; 美国国家射电天文台; 乔治梅森大学; 阿姆斯特丹大学安东·潘内克天文研究所; 乌克兰国家科学院博戈留博夫理论物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究贫金属星系极端发射线来源，发现恒星辐射为主、IMBH小贡献（4-8%）可解释高电离谱线，激波和ULX不足。
AI 中文摘要
极端发射贫金属星系（EEMPGs）是理解早期宇宙极端物理条件和电离辐射场的极佳本地实验室。然而，它们中高电离发射线的确切来源，无论是来自中等质量黑洞（IMBHs）、超亮X射线源（ULXs）还是辐射激波，仍存在争议。我们表征了贫金属EEMPGs的基本性质和电离辐射场，旨在识别驱动这些谱线的高能电离光子的主要来源。我们选取了11个EEMPGs样本，这些是迄今已知的拥有JWST/MIRI观测的最贫金属星系之一（12+log(O/H) < 8.0，或Z/Z$_\bullet$ < 20%）。利用高、低电离势离子的光学和红外诊断图，我们限制了主导其光谱特征的电离源。我们探测到高电离谱线，尤其是所有星系中的He II$\lambda$4686和更广泛的本地EEMPGs样本中42%的[Ne V] 14.3 $\mu$m。多波长诊断图显示，我们的EEMPGs位于通常由活动星系核（AGNs）占据的区域，或介于恒星形成和AGN序列之间。评估产生这些谱线所需的能量，我们发现辐射激波和ULXs不足以解释。相反，我们的分析表明，恒星形成与IMBH的小贡献相结合，提供了足够的高能光子预算，以解释高电离势（> 54 eV）离子的发射线。我们的EEMPG样本覆盖了各种性质，是研究首批星系的理想选择。它们的低和高电离谱线通量比表明恒星辐射可能是电离源，并伴有IMBH的小贡献（4-8%）。纯激波无法解释观测到的发射线比和电离光子预算。
英文摘要
Extreme emission metal-poor galaxies (EEMPGs) are excellent local laboratories for understanding the extreme physical conditions and ionizing radiation fields in the early Universe. However, the exact source of high-ionization emission lines in them, whether from intermediate-mass black holes (IMBHs), ultra-luminous X-ray sources (ULXs), or radiative shocks, remains debated. We characterize the fundamental properties and ionizing radiation field on metal-poor EEMPGs, aiming to identify the dominant sources of the highly ionizing photons that drive these lines. We selected a sample of 11 EEMPGs, among the most metal-poor galaxies with JWST/MIRI observations known so far (12+log(O/H) < 8.0, or Z/Z$_\odot$ < 20%). Using optical and IR diagnostic diagrams for ions of both high and low ionization potential, we constrain the ionization source dominating their spectral features. We detect high-ionization lines, notably He II$λ$4686 in all galaxies and [Ne V] 14.3 $μ$m in 42% of a broader sample of local EEMPGs. The multi-wavelength diagnostic diagrams reveal that our EEMPGs are located in areas that normally are occupied by active galactic nuclei (AGNs) or between the star-formation and AGN sequences. Evaluating the energetics required to produce these lines, we find that radiative shocks and ULXs are not sufficient. Instead, our analysis suggests that a combination of sources with star-formation and a small contribution from an IMBH provide enough high-energy photon budget to explain the emission lines of ions with high-ionization potentials (> 54 eV). Our EEMPG sample, covering various properties, is ideal for studying the first galaxies. Their flux ratios of low- and high-ionization lines suggest stellar radiation as the likely ionization source, with a small contribution from an IMBH (4-8%). Pure shocks fail to explain the observed emission line ratios and ionizing photon budget.
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