标题： 从紫外和光学发射线计算活动星系核的金属丰度 I：碳丰度依赖性 显示英文标题

标题： Metallicity of Active Galactic Nuclei from ultraviolet and optical emission lines I: Carbon abundance dependence

摘要： 金属丰度（$Z$）基于活动星系核（AGN）窄线区（NLRs）的紫外（UV）发射线的估算被发现与来自光学线的那些不同。然而，这种差异（$ZR$）的起源仍然知之甚少。为了调查（$ZR$）的来源，我们从文献中收集了11个AGN样本（9个位于$z<0.4$，2个位于$z\sim2.4$）的窄近紫外（$1000 < \lambda(\angstrom) < 2000)$和光学（$3000 < \lambda(\angstrom) < 7000)$）发射线测量的通量。 金属丰度值是基于一个半经验校准得到的，该校准依赖于 $C43$=log[(\ion \{C{IV}$\lambda$ 1549+\ion \{C{iii}]$\lambda$1909)/\ion{He}{ii}$\lambda$ 1640]发射线比率，并与通过电子温度直接测量（$T_{\rm e}$-方法）和基于光学发射线的校准所获得的值进行了比较。 这一差异的来源通过电离参数（$U$）、电子密度（$N_{\rm e}$）和碳丰度（C/H）进行了研究。我们发现$ZR$、$U$和$N_{\rm e}$之间存在较弱的相关性。然而，$ZR$与直接测量的C/H之间观察到了中等程度的相关性，这表明先前假设用于推导UV碳线校准的光致电离模型中的（C/O）-$Z$关系可能不适用于活动星系核（AGN）。 通过将大量局部恒星形成区域的丰度估计值与我们活动星系核样本的丰度估计值相结合，我们推导出了一个新的(C/O)-$Z$关系。将假设这一新丰度关系的光电离模型结果与我们样本的紫外观测数据进行比较，得出了基于$C43$指数推导的$Z$值，这些值与使用$T_{\rm e}$方法得到的值一致。 显示英文摘要

摘要： Metallicity ($Z$) estimates based on ultraviolet (UV) emission lines from the narrow-line regions (NLRs) of active galactic nuclei (AGNs) have been found to differ from those derived from optical lines. However, the origin of this discrepancy ($ZR$) remains poorly understood. To investigate the source of $ZR$, we compiled from the literature the fluxes of narrow near-UV ($1000 < \lambda(\angstrom) < 2000)$ and optical ($3000 < \lambda(\angstrom) < 7000)$ emission line measurements for a sample of 11 AGNs (9 at $z<0.4$ and 2 at $z\sim2.4$). Metallicity values for our sample were derived using a semi-empirical calibration based on the $C43$=log[(\ion{C{iv}$\lambda$1549+\ion{C{iii}]$\lambda$1909)/\ion{He}{ii}$\lambda$1640] emission-line ratio and compared with those obtained via direct measurement of the electron temperature ($T_{\rm e}$-method) and via calibrations based on optical emission-lines. The source of the discrepancy was investigated in terms of the ionization parameter ($U$), electron density ($N_{\rm e}$), and carbon abundance (C/H). We found a weak correlation between $ZR$, $U$ and $N_{\rm e}$. However, a moderate correlation was observed between $ZR$ and direct estimates of C/H, suggesting that the previously assumed (C/O)-$Z$ relations in photoionization models used to derive UV carbon-line calibrations may not be valid for AGNs. By combining a large set of abundance estimates for local star-forming regions with those of our AGN sample, we derived a new (C/O)-$Z$ relation. Comparisons between the results of photoionization models that assume this new abundance relation and the UV observational data of our sample produce $Z$ values derived from the $C43$ index that are consistent with those obtained using the $T_{\rm e}$-method.