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arXiv 2209.05928astro-ph.GA
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了解分子比率是否可用作AGN和星暴活动的诊断:NGC 1068的情况

Understanding if molecular ratios can be used as diagnostics of AGN and starburst activity: The case of NGC 1068

J. Butterworth, J. Holdship, S. Viti, S. García-Burillo

摘要:

分子谱线比,如HCN(1-0)/HCO $^+$(1-0)和HCN(4-3)/CS(7-6),通常用于识别星系中的活动星系核(AGN)活动。然而,这样的比率很难解释,因为它们高度依赖于气体的物理和能量学,因此很少能被用作唯一的、明确的诊断。我们使用的复合星系NGC 1068作为一个“实验室”,以调查是否HCN,HCO $^+$和CS之间的分子线比是有用的示踪剂的活动星系核占主导地位的气体,并确定在不同类型的气体在这种比例的差异的起源。这样的确定将使得能够更严格地使用这些比率。首先,我们在不同的角分辨率下实证检验上述比率以量化相关性。然后,我们使用局部热力学平衡(LTE)和非LTE分析加上马尔可夫链蒙特卡罗(MCMC)采样,以确定潜在的比率差异的起源。我们认为在高空间分辨率(< 50 pc)下,HCN(4-3)/CS(2-1)是活动星系核活动的可靠示踪剂。我们还发现,比值的变化是不是不同的密度或温度,但不同的分数丰度的后果,产生的重要结果,它是必不可少的考虑化学过程中发挥作用时,从辐射转移计算得出的结论。从不同的空间尺度的分析,我们发现,以前提出的分子线比,以及一个新的,有不同程度的一致性。我们还确定从调查的辐射转移建模我们的数据,它是必不可少的考虑化学的物种时,从辐射转移计算得出的结论。

英文摘要:

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.

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