论文标题
了解分子比是否可以用作AGN和Starburst活性的诊断：NGC 1068的情况
Understanding if molecular ratios can be used as diagnostics of AGN and starburst activity: The case of NGC 1068
论文作者
论文摘要
通常使用分子线比，例如HCN（1-0）/HCO $^+$（1-0）和HCN（4-3）/CS（7-6），以识别星系中的活性银河核（AGN）活性。但是，这种比率很难解释，因为它们高度依赖于气体的物理和能量，因此很少被用作独特的，明确的诊断。我们使用复合星系NGC 1068作为“实验室”来研究HCN，HCO $^+$和CS之间的分子线比是否是AGN主导气体的有用示踪剂，并确定了不同类型气体的差异的起源。这样的决心将使这种比率更加严格。首先，我们在不同角度分辨率下进行了经验检查上述比率以量化相关性。然后，我们使用局部热力学平衡（LTE），并与马尔可夫链蒙特卡洛（MCMC）采样相结合的非LTE分析，以确定比率基本差异的起源。我们建议，在高空间分辨率（<50 PC）下，HCN（4-3）/CS（2-1）是AGN活性的可靠示踪剂。我们还发现，比率的变化不是不同的密度或温度，而是不同分数丰度的结果，从而产生了重要的结果，即在得出辐射转移计算得出结论时，必须考虑在起作用的化学过程。从不同空间尺度的分析中，我们发现先前提出的分子线比以及新的分子线比具有不同水平的一致性。我们还根据对数据的辐射转移模型的研究确定，在从辐射转移计算得出的结论时，必须考虑物种的化学反应。
Molecular line ratios, such as HCN(1-0)/HCO$^+$(1-0) and HCN(4-3)/CS(7-6), are routinely used to identify active galactic nuclei (AGN) activity in galaxies. Such ratios are, however, hard to interpret as they are highly dependent on the physics and energetics of the gas, and hence can seldom be used as a unique, unambiguous diagnostic. We used the composite galaxy NGC 1068 as a `laboratory' to investigate whether molecular line ratios between HCN, HCO$^+$, and CS are useful tracers of AGN-dominated gas and determine the origin of the differences in such ratios across different types of gas. Such a determination will enable a more rigorous use of such ratios. First, we empirically examined the aforementioned ratios at different angular resolutions to quantify correlations. We then used local thermodynamic equilibrium (LTE) and non-LTE analyses coupled with Markov chain Monte Carlo (MCMC) sampling in order to determine the origin of the underlying differences in ratios. We propose that at high spatial resolution (< 50 pc) the HCN(4-3)/CS(2-1) is a reliable tracer of AGN activity. We also find that the variations in ratios are not a consequence of different densities or temperature but of different fractional abundances, yielding to the important result that it is essential to consider the chemical processes at play when drawing conclusions from radiative transfer calculations. From analyses at varying spatial scales, we find that previously proposed molecular line ratios, as well as a new one, have varying levels of consistency. We also determine from an investigation of radiative transfer modelling of our data that it is essential to consider the chemistry of the species when reaching conclusions from radiative transfer calculations.
