在无恒星形成、被动演化的星系中，以低电离物种为主的发射线区域被归类为低电离发射区（Low-Ionization Emission Regions, LIERs）。这类区域背后的电离机制长期以来一直是个谜。曾被认为是其电离源的活动星系核（Active Galactic Nuclei, AGNs），已被发现并非主导机制，尤其是在远离星系核的区域。剩余的候选机制——后渐近巨星支（post-Asymtopic Giant Branch, pAGB）恒星的光致电离和星际激波——只有通过深入分析才能区分。由于这两种模型的温度预测存在差异，温度测量可以为这一谜题提供强有力的约束。我们从斯隆数字巡天IV（Sloan Digital Sky Survey IV, SDSS-IV）的阿帕奇点天文台近邻星系测绘（Mapping Nearby Galaxies at Apache Point Observatory, MaNGA）巡天中选取了2795个宁静红序星系的样本。我们根据样本光谱的[N II]/Hα 流量比将其分为三组，并利用叠加技术提高观测光谱的信噪比。我们通过[O III]、[N II]、[S II]和[O II]的温度敏感发射线比测定了它们的温度。随后，我们将测得的温度与不同模型的预测结果进行了比较。结果表明，测量值与预激波密度n = 1 cm⁻³、太阳金属丰度的星际激波模型一致，从而支持激波是LIERs的主导电离源。此外，我们还发现，通过巴耳末减幅测得的星际尘埃消光值似乎大于低电离线的禁线比所暗示的消光值。
英文摘要：
In non-star-forming, passively evolving galaxies, regions with emission lines dominated by low-ionization species are classified as Low-Ionization Emission Regions (LIERs). The ionization mechanism behind such regions has long been a mystery. Active Galactic Nuclei (AGNs), which were once believed to be the source, have been found not to be the dominant mechanism, especially in regions distant from the galaxy nuclei. The remaining candidates, photoionization by post-Asymtopic Giant Branch (pAGB) stars and interstellar shocks can only be distinguished with in-depth analysis. As the temperature predictions of these two models differ, temperature measurements can provide strong constraints on this puzzle. We selected a sample of 2795 quiescent red-sequence galaxies from the Sloan Digital Sky Survey IV (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We divided the sample spectra into three groups based on their [N II]/H$α$ flux ratio and utilized stacking techniques to improve the signal-to-noise ratio of the observed spectra. We determined the temperature of [O III], [N II], [S II], and [O II] through their temperature-sensitive emission line ratios. Subsequently, we compared the measured temperatures with predictions from different models. The results demonstrate consistency with the interstellar shock model with preshock density n = 1 cm$^{-3}$ and solar metallicity, thus supporting shocks as the dominant ionization source of LIERs. Additionally, we also find that the interstellar dust extinction value measured through the Balmer decrement appears to be larger than that implied by the forbidden line ratios of low-ionization lines.
Highly Ionized Oxygen in the Circumgalactic Medium of TNG100 Galaxies: Distributions, Thermal States, and Ionization Mechanisms
School of Physics and Astronomy, Tel Aviv University（特拉维夫大学物理与天文学学院）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Max-Planck-Institut für extraterrestrische Physik (MPE)（马克斯·普朗克地外物理学研究所）；Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）
JWST reveals a highly ionized nebula powered by an ultraluminous X-ray source with a massive black hole in the metal-poor galaxy Holmberg II
Space Telescope Science Institute（太空望远镜科学研究所）；AURA for ESA, Space Telescope Science Institute（欧洲航天局天文研究联盟，太空望远镜科学研究所）；Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；Sterrenkundig Observatorium, Universiteit Gent（根特大学天文台）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所（地球物理与化学研究所，西班牙国家研究委员会））；Centro de Astrobiología – Departamento de Astrofísica (CSIC-INTA)（天体生物学中心 - 天体物理学系（西班牙国家研究委员会-国家航空航天技术研究所））
本研究通过JWST光谱观测，首次在ULX Ho II X-1周围探测到[Ne V]和[Ne VI]，直接证实该ULX关联低金属丰度星系中的高度电离星云，其电离由吸积黑洞驱动，电离条件呈各向异性。
