Extragalactic nebular emission line analysis with realistic EUV spectral energy distributions of massive stars of different metallicities as a tool for measuring interstellar chemical abundances

氢区在测量星际介质的化学成分方面起着至关重要的作用。与行星状星云一样，它们也是原子物理学的实验室，提供了有关重元素丰度的基本数据，这些数据制约了星系化学演化模型。然而，观测到的发射线强度与星云模型预测的发射线强度之间仍然存在重大差异。这些差异不能简单地归因于星云化学丰度的变化，因此表明我们对这些发射线系统的理解存在更根本的缺陷。在模拟H区的不确定性中，最重要的是关于电离辐射源的光谱能量分布（SED）的问题，这些辐射源通常是光谱类型为O的热恒星。由于电离光谱范围内的辐射由于星际介质的吸收而不能直接观测到，星云模型必须依赖于恒星大气模型预测的SED。间接地，比较观测到的发射线强度和星云模型预测的发射线强度，从而也提供了一种方法来验证恒星大气模型预测的SED。只有当星云模型和恒星模型的结合能够可靠地再现观测结果时，星云诊断才能充分发挥其作为测量星际丰度的定量工具的潜力。影响星云光谱的关键因素之一是星云和恒星的金属丰度（重元素的丰度）。星系内金属丰度的径向梯度的存在是有据可查的，从一个星系到另一个星系的总体金属丰度的差异也是如此。但是，尽管星云建模往往涉及测试不同的星云金属丰度对预测光谱的影响，恒星大气的足够的网格和不同金属丰度的现实SED仍然缺失。这是令人反感的，因为恒星的金属丰度对星云线强度比的影响，通过其对SED的影响，已被证明是甚至大于在星云metallicity.In这个项目中，我们建议研究一个大样本的H-10区域的不同金属丰度-从超级太阳能显着subsolar -使用一个一致的网格模型大气SED涵盖了大范围的金属丰度。我们将使用最先进的模型大气计算这些SED，这些模型大气始终考虑到重元素谱线对电离通量的衰减以及辐射驱动风的流体动力学及其对SED的影响。这个SED网格，加上详细的星云模型和斯皮策太空望远镜对H2O区域进行的高质量观测（我们可以从第1和第2周期的两次完整观测中获得这些观测结果），将提供一个有用的工具来约束银河系化学演化的模型。

H װ regions play a crucial role in the measurement of the chemical composition of the interstellar medium. Like planetary nebulae, they serve as laboratories for atomic physics and provide fundamental data about heavy element abundances that constrain models of galactic chemical evolution.However, major discrepancies still exist between observed emission line strengths and those predicted by nebular models. These discrepancies cannot simply be attributed to variations in the nebular chemical abundances, and thus indicate a more fundamental deficiency in our understanding of these emission line systems. Foremost among the uncertainties in modelling H װ regions are issues concerning the spectral energy distribution (SED) of the ionizing radiation source, most often hot stars of spectral type O . Since the radiation in the ionizing spectral range cannot be directly observed because of absorption in the interstellar medium, nebular models must rely on SEDs predicted by stellar atmosphere models. Indirectly, the comparison of observed emission line strengths and those predicted by nebular models thus also offers a way to verify the SEDs predicted by stellar atmosphere models. Only when the combination of nebular and stellar models is reliably shown to reproduce the observations can nebular diagnostics be used to its full potential as a quantitative tool for measuring interstellar abundances.One of the key influences on the nebular spectra is the metallicity (the abundance of heavy elements), both nebular and stellar. The existence of radial gradients of the metallicity within galaxies is well documented, as are differences in overall metallicity from one galaxy to another. But whereas nebular modelling often involves testing of different nebular metallicities against their influence on the predicted spectra, adequate grids of stellar atmospheres and realistic SEDs for different metallicities are still missing. This is objectionable because the influence of stellar metallicity on nebular line strength ratios, via its effect on the SEDs, has been shown to be even larger than that of variations in the nebular metallicity.In this project we propose to study a large sample of H װ regions of different metallicities - from super-solar to significantly subsolar - using a consistent grid of model atmosphere SEDs covering a large range of metallicities. These SEDs will be computed by us using state-of-the-art model atmospheres that consistently take into account the attenuation of the ionizing flux by the spectral lines of heavy elements and the hydrodynamics of the radiatively driven wind and its influence on the SEDs. This grid of SEDs, together with detailed nebular models and available high-quality observations of H װ regions taken with the Spitzer Space Telescope - the observations are available to us from two completed observing runs in Cycles 1 and 2 -, will provide a useful tool to constrain models for galactic chemical evolution.