A λ = 3 mm molecular line survey of NGC 1068 . Chemical signatures of an AGN environment
A λ = 3 mm molecular line survey of NGC 1068 . Chemical signatures of an AGN environment
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NGC 1068 的 λ = 3 mm 分子谱线调查 AGN 环境的化学特征。
DOI：
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发表时间：
2021
期刊：
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通讯作者：
A. Weiss
中科院分区：
文献类型：
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作者：
R. Aladro;S. Viti;E. Bayet;D. Riquelme;S. Martín;R. Mauersberger;J. Martín;A. M.;Requena;C. Kramer;A. Weiss
目标。通过对活动星系核（AGN）周围星际介质（ISM）的分子种类及其丰度的清点，研究其分子组成。建立星暴星系和活动星系核之间的化学差异。方法.我们用IRAM-30 m望远镜观测了NGC 1068的中心1.5- 2k pc区域，覆盖频率在86.2 - 115.6GHz之间。利用玻尔兹曼图计算了被测分子的柱密度。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，宇宙射线和冲击对ISM的影响。结果其中HC 3 N、SO、N2 H、CH 3CN、NS、13 CN和HN 13 C是首次在NGC 1068中发现的。通过对NGC 1068、M82和NGC 253核区丰度的比较，我们建立了星暴星系与活动星系核之间的化学差异。H2 CO和CH 3CCH是星暴星系中含量丰富的两种物质，在NGC 1068中没有检测到，可能是因为它们被紫外光场或激波破坏了。另一方面，物种，如CN，SiO，HCO +和HCN，宇宙射线辐射场增强。得到了同位素比值的上限值：12 C/13 C =49，16 O/18 O =177，32 S/34 S =5。这些比率在活动星系核中要比在星暴星系核中低得多。我们的化学模型表明，NGC 1068核中的化学物质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。C-shocks可以解释C_2H和H_2CO的丰度，但对其他物种的丰度影响不大。结论. 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。
Aims. To study the molecular composition of the interstellar medi um (ISM) surrounding an Active Galactic Nucleus (AGN), by making an inventory of molecular species and their abundanc es. To establish a chemical di fferentiation between starburst galaxies and AGN. Methods. We used the IRAM-30 m telescope to observe the central 1.5-2 k pc region of NGC 1068, covering the frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we calcula ted 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 th influence of UV fields, cosmic rays, and shocks on the ISM. Results. We identified 24 di fferent molecular species and isotopologues, among which HC 3N, SO, N2H, CH3CN, NS,13CN, and HN13C are detected for the first time in NGC 1068. A comparison of th e abundances in the nuclear regions of NGC 1068, M 82 and NGC 253 allowed us to establish a chemical di fferentiation between starburst galaxies and AGN. H 2CO and CH3CCH, two abundant species in starburst galaxies, are not detected in NGC 1068, probably because they are destroyed by UV fields or shocks. On the other hand, species such as CN, SiO, HCO + and HCN, are enhanced by cosmic ray radiation fields. We obtai ned the upper limits to the isotopic ratios12C / 13C=49, 16O / 18O=177 and32S/ 34S=5. These ratios are much lower in this AGN than in starburst ga laxies. Our chemical models suggest that the chemistry in the nucleus of NGC 1068 is strongly influenced by cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV) radiation field s also explain well the observations. C-shocks can explain t he abundances of C2H and H2CO, but do not strongly a ffect the abundances of the other detected species. Conclusions. The gas in the nucleus of NGC 1068 has a di fferent chemical composition as compared to starburst galaxi es. The distinct physical processes dominating galaxy nuclei (e.g. C-shock s, UV fields, X-rays, cosmic rays) leave clear imprints in the c mistry of the gas, which allow to characterise the nucleus activity by its molecular abundances.