NGC1068的λ =3 mm分子线测量。AGN环境的化学特征
A lambda=3 mm molecular line survey of NGC1068. Chemical signatures of an AGN environment
摘要：
我们的目标是研究围绕活动星系核（AGN）的星际介质（ISM）的分子组成，通过对分子种类及其丰度的清点，以及建立星爆星系和AGN之间的化学差异。我们用IRAM-30 m望远镜观测了NGC 1068中心1.5-2 kpc区域，覆盖频率在86.2 GHz和115.6 GHz之间。利用玻尔兹曼图，我们计算了检测到的分子的柱密度。我们使用了一个化学模型来重现活动星系核中发现的丰度，以确定每个检测到的物种的起源，并测试紫外线场，宇宙射线，和冲击的ISM的影响。我们鉴定了24种不同的分子种类和同位素体，其中HC 3 N，SO，N2 H+，CH 3CN，NS，13 CN和HN 13 C是首次在NGC 1068中检测到的。我们得到了同位素比值12 C/13 C =49，16 O/18 O =177和32 S/34 S =5的上限。我们的化学模型表明，NGC 1068的原子核中的化学成分受到宇宙射线的强烈影响，尽管宇宙射线和远紫外（FUV）辐射场的高值也很好地解释了观测结果。NGC 1068的核心气体与星暴星系相比具有不同的化学成分。支配星系核的独特物理过程（例如C激波、紫外线场、X射线、宇宙射线）在气体的化学性质中留下了清晰的印记，这使得可以通过其分子丰度来确定核的活动。
英文摘要：
We aimed to study the molecular composition of the interstellar medium (ISM) surrounding an Active Galactic Nucleus (AGN), by making an inventory of molecular species and their abundances, as well as to establish a chemical differentiation between starburst galaxies and AGN. We used the IRAM-30 m telescope to observe the central 1.5-2 kpc region of NGC1068, covering the frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we calculated the column densities of the detected molecules. We used a chemical model to reproduce the abundances found in the AGN, to determine the origin of each detected species, and to test the influence of UV fields, cosmic rays, and shocks on the ISM. We identified 24 different molecular species and isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are detected for the first time in NGC1068. We obtained the upper limits to the isotopic ratios 12C/13C=49, 16O/18O=177 and 32S/34S=5. Our chemical models suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV) radiation fields also explain well the observations. The gas in the nucleus of NGC1068 has a different chemical composition as compared to starburst galaxies. The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas, which allow to characterise the nucleus activity by its molecular abundances.
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