Numerical models for the diffuse ionized gas in galaxies
Numerical models for the diffuse ionized gas in galaxies
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星系中扩散电离气体的数值模型
DOI：
10.1051/0004-6361/201832649
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发表时间：
2019
影响因子：
6.5
通讯作者：
Hoffmann T. L.
中科院分区：
文献类型：
--
作者：
Weber J. A;Pauldrach A. W. A.;Hoffmann T. L.
弥漫电离气体（DIG）构成了恒星形成星系中总电离星际物质的最大部分，但仍然不清楚电离是否主要由热质量恒星的电离辐射驱动，如H II区域，或者是否必须考虑其他电离源。理解DIG中电离机制的关键是电离气体的线发射。AimsWe系统地探索了参数空间的一个合理子集，涉及电离源的有效温度和金属丰度，周围具有不同逃逸分数的"泄漏" H II区域对其辐射的硬化效应，以及DIG的块状性的不同情景，和计算产生的线强度比的一些诊断光emission line.MethodsFor的电离通量，我们计算了一个网格的恒星光谱能量分布（SED）从详细的，完全非LTE模型的大气，包括恒星风和线阻塞和覆盖的影响。为了计算星际气体中的电离和温度结构，我们使用了球对称光电离模型和最先进的三维（3D）非LTE辐射传输模拟，考虑了氢，氦和最丰富的金属。我们首先将这些方法应用于热恒星周围的经典H II区，使用模型SED在不同的金属丰度和有效温度的电离通量，并计算不同逃逸分数的氢电离光子逃逸辐射的SED。在第二步中，我们研究了逃逸辐射对更稀和更长的DIG的影响。使用3D模型模拟一个银河系旋臂的一部分，我们计算了电离结构的DIG为不同的情况下的气体的不均匀性，假设电离的恒星人口SED的基础上合理的parameters.ResultsWe提供定量预测如何从H II地区和DIG的线比变化作为一个函数的metallicityZ，恒星有效temperatureTeff，以及H II区的逃逸分数。预测线比的范围加强了DIG被来自热恒星的辐射电离（过滤）的假设。在十分之一的太阳金属丰度下，辐射硬化主要是由于氢和氦，而在太阳金属丰度下，金属的吸收起着重要作用。硬化效应主要表现在气体最重要的冷却线的发射线比率的增加上，在较低的Teff下，[N II] scinH β和[O II] scinH β，在较高的Teff下，[O III] scinH β。对于lowTeffalmost整个He I电离辐射被吸收的H II区域，从而防止形成高电离阶段，如O III的DIG。DIG的电离结构强烈地依赖于气体的聚集因子和大尺度分布。在我们的模拟中，大约10%的电离辐射产生的热的大质量恒星在一个螺旋臂是足够的dig高达约1千秒差距以上的银道面的聚集因子接近观察值offcl~5的高度。即使模拟参数（如聚集因子）的微小变化也会导致电离体积的显著变化。对于一个更均匀的气体和一个非常不均匀的气体，其中既有致密的团块，又有低密度的通道，银河系平面上方的稀气体中的电离区域可以停止辐射约束，允许电离辐射泄漏到星系际介质中。观测和预测的线比的比较表明，DIG是…
ContextThe diffuse ionized gas (DIG) constitutes the largest fraction of the total ionized interstellar matter in star-forming galaxies, but it is still unclear whether the ionization is driven predominantly by the ionizing radiation of hot massive stars, as in H II regions, or whether additional sources of ionization have to be considered. Key to understanding the ionization mechanisms in the DIG is the line emission by the ionized gas.AimsWe systematically explore a plausible subset of the parameter space involving effective temperatures and metallicities of the ionizing sources, the effects of the hardening of their radiation by surrounding “leaky” H II regions with different escape fractions, as well as different scenarios for the clumpiness of the DIG, and compute the resulting line strength ratios for a number of diagnostic optical emission lines.MethodsFor the ionizing fluxes we computed a grid of stellar spectral energy distributions (SEDs) from detailed, fully non-LTE model atmospheres that include the effects of stellar winds and line blocking and blanketing. To calculate the ionization and temperature structure in the interstellar gas we used spherically symmetric photoionization models and state-of-the-art three-dimensional (3D) non-LTE radiative transfer simulations, considering hydrogen, helium, and the most abundant metals. We first applied these methods to classical H II regions around hot stars, using the model SEDs at different metallicities and effective temperatures as ionizing fluxes, and compute the SEDs of the escaping radiation for different escape fractions of hydrogen-ionizing photons. In a second step, we studied the effects of the escaping radiation on the more dilute and extended DIG. Using 3D models simulating a section of a galactic spiral arm, we computed the ionization structure in the DIG for different scenarios for the inhomogeneity of the gas, assuming ionization by a stellar population SED based on plausible parameters.ResultsWe provide quantitative predictions of how the line ratios from H II regions and the DIG vary as a function of metallicityZ, stellar effective temperatureTeff, and escape fractionfescfrom the H II region. The range of predicted line ratios reinforces the hypothesis that the DIG is ionized by (filtered) radiation from hot stars. At one-tenth solar metallicity, radiation hardening is mostly due to hydrogen and helium, whereas at solar metallicity absorption by metals plays a significant role. The effects of hardening are seen primarily in the increase in the emission line ratios of the most important cooling lines of the gas, [N II]∕Hβand [O II]∕Hβat lowerTeff, and [O III]∕Hβat higherTeff. For lowTeffnearly the entire He I-ionizing radiation is absorbed in the H II regions, thereby preventing the formation of high ionization stages such as O III in the DIG. The ionization structure of the DIG depends strongly on both the clumping factor and the large-scale distribution of the gas. In our simulations about 10% of the ionizing radiation produced by hot massive stars in a spiral arm is sufficient to ionize the DIG up to a height of approximately 1 kpc above the galactic plane for a clumping factor close to the observed value offcl~ 5. Even small changes in simulation parameters such as the clumping factor can lead to considerable variation in the ionized volume. Both for a more homogeneous gas and a very inhomogeneous gas containing both dense clumps and channels with low gas density, the ionized region in the dilute gas above the galactic plane can cease to be radiation-bounded, allowing the ionizing radiation to leak into the intergalactic medium. Comparison of observed and predicted line ratios indicates that the DIG is …
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寻找额外的加热：NGC 891、NGC 4631 和 NGC 3079 的扩散电离气体中的 [O II] 发射
DOI：
10.1086/322343
发表时间：
2001
期刊：
The Astrophysical Journal
影响因子：
--
作者：
B. Otte;R. J. Reynolds;J. Gallagher III;A. Ferguson
通讯作者：
A. Ferguson
阿尔文波丝加热等离子体：日冕和星际介质中的相关机制
DOI：
10.1086/304504
发表时间：
1997
期刊：
The Astrophysical Journal
影响因子：
--
作者：
S. Champeaux;A. Gazol;T. Passot;P. Sulem
通讯作者：
P. Sulem
聚集对 Hii 地区衍生丰度的影响
DOI：
--
发表时间：
2005
期刊：
影响因子：
--
作者：
J. Mathis;Kenneth Wood The University of Wisconsin;U. S. Andrews
通讯作者：
U. S. Andrews
从弥漫星际介质中寻找 He I lambda 5876 重组线
DOI：
--
发表时间：
1995
期刊：
影响因子：
--
作者：
R. J. Reynolds;S. Tufte
通讯作者：
S. Tufte
DOI：
10.1086/167912
发表时间：
1989-10
期刊：
The Astrophysical Journal
影响因子：
--
作者：
C. Norman;S. Ikeuchi
通讯作者：
C. Norman;S. Ikeuchi