Consequences of Dust in Metal-rich H II Regions
Consequences of Dust in Metal-rich H II Regions
复制标题
富含金属 H II 区域的灰尘后果
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
R. Kennicutt
中科院分区：
文献类型：
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作者：
J. Shields;R. Kennicutt
尘埃和相关的重元素从气相耗尽可以修改从无尘的情况下的HII区域的热性质，具有显着的后果的出现的光谱。我们提出的理论计算结果，说明了巨大的，河外HII地区的光谱上的颗粒的影响，重点是高金属丰度系统（即太阳和更高的Z）。尘埃提供了一个简单的解释，为观测缺乏纯巴耳末线光谱，预计在理论上的基础上，无尘，化学丰富的星云。颗粒也可能发挥作用，在HII地区的正常星系的富集核中观察到的禁止线发射的增强。在大多数情况下，耗尽对光谱引入最强的扰动。然而，在某些情况下，电离连续谱的选择性吸收以及晶粒光电子的加热是重要的，并且晶粒加热对于增强高电离谱线中的发射可以是特别重要的。考虑到损耗，尘埃的存在不太可能在全球金属丰度指标中引入大的误差，尽管损耗因子的不确定性加上红外冷却对电子密度的敏感性将使高Z下的准确校准变得困难。目前的计算进一步确定，以前的相对丰度分析，未能考虑到尘埃的影响，在一个自洽的方式（粮食加热以及耗尽）可能高估了高Z星云的温度梯度，导致错误的相对丰度为不同的元素。
Dust and associated depletion of heavy elements from the gas phase can modify the thermal properties of HII regions from the dust-free case, with significant consequences for the emergent optical spectrum. We present the results of theoretical calculations illustrating the effects of grains on the spectra of giant, extragalactic HII regions, with emphasis on high metallicity systems (i.e. solar and higher Z). Dust provides a simple explanation for the observational absence of pure Balmer-line spectra that are expected on theoretical grounds for dust-free, chemically enriched nebulae. Grains may also play a role in enhancements of forbidden-line emission observed in HII regions in the enriched nuclei of normal galaxies. In most cases, depletion introduces the strongest perturbations to the optical spectrum. Selective absorption of the ionizing continuum as well as heating by grain photoelectrons are important in some instances, however, and grain heating can be particularly important for enhancing emission in high-ionization lines. Allowing for depletion, the presence of dust is unlikely to introduce large errors in global metallicity indicators, although uncertainties in depletion factors coupled with the sensitivity of infrared cooling to electron density will make accurate calibrations difficult at high Z. The present calculations establish further that previous relative abundance analyses that fail to take into account dust effects in a self-consistent way (grain heating as well as depletion) may overestimate temperature gradients in high-Z nebulae, resulting in errors in relative abundances for different elements.