从红外星云谱线测量AGN的化学丰度：AGN的HII-CHI-Mistry-IR
Measuring chemical abundances in AGN from infrared nebular lines: HII-CHI-Mistry-IR for AGN
摘要：
未来和正在进行的红外和射电天文台（例如JWST、METIS或ALMA）将使星系的静止框架红外光谱数据量增加几个数量级。虽然基于光学观测的ISM的化学成分的研究已经广泛传播了几十年的SFG，最近，AGN，类似的研究需要使用IR数据进行。这种机制在活动星系核的情况下特别有用，因为它受温度和尘埃消光的影响较小，可以追踪更高的离子种类，还可以提供对化学丰度比N/O的可靠估计。我们提出了一个新的工具的基础上贝叶斯的方法来估计化学丰度的红外线发射线在活动星系核。我们使用了一个58个活动星系核的红外光谱数据，从文献中检索，以探讨我们的方法的有效性。我们的样品中的红外线的基础上的化学丰度的估计随后与来自相同对象中的光学发射线的相应的丰度进行比较。HII-CHI-Mistry-IR利用光电离模型，其特征在于化学丰度比O/H和N/O和电离参数$U$，比较它们预测的发射线通量与一组观测值。该代码使用对上述自由参数敏感的特定发射线比，而不是匹配单个发射线。我们报告主要是太阳和太阳下的O/H在我们的样本AGN的核区域的丰度，而N/O集群太阳值。我们发现来自IR和光学发射线的化学丰度之间的差异，是后者高于前者。这种差异，也报告了以前的研究组成的ISM活动星系核的红外观测，是独立的气体密度或入射辐射场的气体。
英文摘要：
Future and on-going infrared and radio observatories such as JWST, METIS or ALMA will increase the amount of rest-frame IR spectroscopic data for galaxies by several orders of magnitude. While studies of the chemical composition of the ISM based on optical observations have been widely spread over decades for SFG and, more recently, for AGN, similar studies need to be performed using IR data. This regime can be especially useful in the case of AGN given that it is less affected by temperature and dust extinction, traces higher ionic species and can also provide robust estimations of the chemical abundance ratio N/O. We present a new tool based on a bayesian-like methodology to estimate chemical abundances from IR emission lines in AGN. We use a sample of 58 AGN with IR spectroscopic data retrieved from the literature to probe the validity of our method. The estimations of the chemical abundances based on IR lines in our sample are later compared with the corresponding abundances derived from the optical emission lines in the same objects. HII-CHI-Mistry-IR takes advantage of photoionization models, characterized by the chemical abundance ratios O/H and N/O and the ionization parameter $U$, to compare their predicted emission-line fluxes with a set of observed values. Instead of matching single emission lines, the code uses some specific emission-line ratios sensitive to the above free parameters. We report mainly solar and also subsolar abundances for O/H in the nuclear region for our sample of AGN, whereas N/O clusters around solar values. We find a discrepancy between the chemical abundances derived from IR and optical emission lines, being the latter higher than the former. This discrepancy, also reported by previous studies of the composition of the ISM in AGN from IR observations, is independent from the gas density or the incident radiation field to the gas.
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