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arXiv 2409.16062astro-ph.GA
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Cloudy建模表明盘外弥漫气体存在多种电离机制

Cloudy modeling suggests a diversity of ionization mechanisms for diffuse extraplanar gas

R. P. V. Rautio, H. Salo, A. E. Watkins, S. Comerón, A. Venhola

AI总结:

研究利用MUSE观测8个近邻侧视盘星系,通过Cloudy建模分析eDIG的电离辐射来源,发现银道面HII区域泄漏辐射是主要电离源,但在低恒星形成率星系中原位演化恒星电离作用显著。

摘要:

远离高能银道面OB星的弥漫气体电离现象,对OB星辐射是星系气体主要电离源这一普遍观点构成了挑战。我们利用Multi Unit Spectroscopic Explorer (MUSE)对8个近邻(17-52 Mpc)侧视盘星系样本进行了观测,研究了其盘外弥漫电离气体(eDIG)中的电离辐射来源,特别是泄漏的银道面HII区域和/或原位低质量演化恒星(HOLMES)。我们通过多次运行Cloudy光致电离代码,构建了eDIG云光致电离及电离辐射在eDIG中传播的模型。该模型包含源自银道面OB星和原位演化恒星的辐射,及其在eDIG中传播时的稀释与处理过程。我们利用样本星系的垂直线强比剖面将模型拟合至数据,发现对于样本中的多数星系,原位演化恒星的电离作用微不足道,但它可能能够解释绿谷星系ESO 544-27的eDIG中增强的高电离谱线。结果表明,尽管银道面HII区域泄漏的辐射是eDIG的主要电离源,但在低恒星形成率的星系中,原位演化恒星在电离盘外气体方面可发挥重要作用。

英文摘要:

The ionization of diffuse gas located far above the energetic midplane OB stars poses a challenge to the commonly accepted notion that radiation from OB stars is the primary ionization source for gas in galaxies. We investigated the sources of ionizing radiation, specifically leaking midplane HII regions and/or in situ hot low-mass evolved stars (HOLMES), in extraplanar diffuse ionized gas (eDIG) in a sample of eight nearby (17-52 Mpc) edge-on disk galaxies observed with the Multi Unit Spectroscopic Explorer (MUSE). We constructed a model for the photoionization of eDIG clouds and the propagation of ionizing radiation through the eDIG using subsequent runs of Cloudy photoionization code. Our model includes radiation originating both from midplane OB stars and in situ evolved stars and its dilution and processing as it propagates in the eDIG. We fit the model to the data using the vertical line ratio profiles of our sample galaxies, and find that while the ionization by in situ evolved stars is insignificant for most of the galaxies in our sample, it may be able to explain the enhanced high-ionization lines in the eDIG of the green valley galaxy ESO 544-27. Our results show that while leaking radiation from midplane HII regions is the primary ionization source for eDIG, in situ evolved stars can play a significant part in ionizing extraplanar gas in galaxies with low star forming rates.

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