The Herschel Dwarf Galaxy Survey
The Herschel Dwarf Galaxy Survey
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DOI：
10.1051/0004-6361/201834457
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发表时间：
2019-04
影响因子：
6.5
通讯作者：
D. Cormier;N. Abel;S. Hony;V. Lebouteiller;S. Madden;F. Polles;F. Galliano;I. D. Looze;M. Galametz;A. Lambert-Huyghe
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文献类型：
--
作者：
D. Cormier;N. Abel;S. Hony;V. Lebouteiller;S. Madden;F. Polles;F. Galliano;I. D. Looze;M. Galametz;A. Lambert-Huyghe
灵敏的红外望远镜，斯皮策和赫歇尔，已经被用来瞄准低金属丰度的恒星形成星系，使我们能够前所未有地详细地研究它们的星际介质(ISM)的性质。用物理术语解释观测结果有赖于对这些特性的仔细建模。我们用多相方法用光谱合成程序Cloudy模拟了ISM相(HⅡ区和光解离区)。我们的目标是描述物理条件(气体密度、辐射场等)。在赫歇尔矮星系调查的星系的ISM中。我们特别感兴趣的是这些物理条件与金属丰度或恒星形成活动之间的关系。我们已经解决的其他关键问题是不同的ISM相对总线发射的贡献，特别是[C II]157μm线，以及ISM的孔隙率的表征。我们发现，我们的样本中金属丰度较低的星系往往具有较高的电离参数，具有较高比恒星形成率的星系具有较高的气体密度。[C II]排放主要来自PDR，电离气相的贡献很小，通常不到观测排放量的30%。我们还发现金属丰度与PdR复盖因子和电离气体中的[C II]分数之间存在相关性--尽管是分散的。总体而言，低金属丰度似乎是这些星系ISM结构和条件变化的主要原因，而不是高的特定恒星形成率。这些结果定量地证明了低金属度时ISM孔隙率的增加。这种孔洞可能是年轻宇宙中星系的典型特征。
The sensitive infrared telescopes, Spitzer and Herschel, have been used to target low-metallicity star-forming galaxies, allowing us to investigate the properties of their interstellar medium (ISM) in unprecedented detail. Interpretation of the observations in physical terms relies on careful modeling of those properties. We have employed a multiphase approach to model the ISM phases (H II region and photodissociation region) with the spectral synthesis code Cloudy. Our goal is to characterize the physical conditions (gas densities, radiation fields, etc.) in the ISM of the galaxies from the Herschel Dwarf Galaxy Survey. We are particularly interested in correlations between those physical conditions and metallicity or star-formation activity. Other key issues we have addressed are the contribution of different ISM phases to the total line emission, especially of the [C II]157 μm line, and the characterization of the porosity of the ISM. We find that the lower-metallicity galaxies of our sample tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [C II] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation – though with scatter – between metallicity and both the PDR covering factor and the fraction of [C II] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity. Such porosity may be typical of galaxies in the young Universe.