AGN中的分子气体化学。II。NGC1068中SiO发射的高分辨率成像：电击还是XDR？
Molecular gas chemistry in AGN. II. High-resolution imaging of SiO emission in NGC1068: shocks or XDR?
摘要：
本文是Seyfert 2星系NGC 1068环核盘（CND）分子气体线发射多物种调查的一部分。单碟观测提供的证据表明，在NGC 1068的CND的一氧化硅（SiO）的丰度是由3-4个数量级相对于通常在银河系中的静态分子气体测量值增强。我们的目标是揭示SiO增强的机制。我们用IRAM Plateau de Bure干涉仪对NGC 1068中SiO（2-1）和CN（2- 1）谱线的发射进行了成像，空间分辨率分别为150 pc和60 pc。我们还获得了HNCO和甲醇（CH_3OH）谱线的互补IRAM 30 m观测结果。在活动星系核周围的一个400 pc大小的盘中检测到SiO。（1-5）xE-09的CND中的SiO丰度比星暴环中的高出1-2个数量级。CND中氯化萘的总体丰度较高：（0.2-1）xE-07。SiO和CN的丰度在活动星系核附近（r<70 pc）与非圆运动有关的气体的极端速度下增加。CN和SiO的丰度以及CN/CO和SiO/CO比值与硬X射线辐照的相关性表明，NGC 1068的CND已成为一个巨大的X射线主导区（XDR）。在NGC 1068的环核分子盘中，分子气体的极端性质是由与核活动直接相关的不同过程之间的相互作用造成的。尽管XDR化学对NGC 1068中的CN和SiO提供了一个简单的解释，但冲击的相关性值得进一步研究。包含尘埃颗粒化学将有助于解决关于其他分子物种丰度的争议，如HCN，XDR模型预测不足。
英文摘要：
This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC1068. Single-dish observations have provided evidence that the abundance of silicon monoxide(SiO) in the CND of NGC1068 is enhanced by 3-4 orders of magnitude with respect to the values typically measured in quiescent molecular gas in the Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. We have imaged with the IRAM Plateau de Bure interferometer the emission of the SiO(2-1) and CN(2--1) lines in NGC1068 at 150pc and 60pc spatial resolution, respectively. We have also obtained complementary IRAM 30m observations of HNCO and methanol (CH3OH) lines. SiO is detected in a disk of 400pc size around the AGN. SiO abundances in the CND of (1-5)xE-09 are about 1-2 orders of magnitude above those measured in the starburst ring. The overall abundance of CN in the CND is high: (0.2-1)xE-07. The abundances of SiO and CN are enhanced at the extreme velocities of gas associated with non-circular motions close to the AGN (r<70pc). Abundances measured for CN and SiO, and the correlation of CN/CO and SiO/CO ratios with hard X-ray irradiation, suggest that the CND of NGC1068 has become a giant X-ray dominated region (XDR). The extreme properties of molecular gas in the circum-nuclear molecular disk of NGC1068 result from the interplay between different processes directly linked to nuclear activity. Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC1068, the relevance of shocks deserves further scrutiny. The inclusion of dust grain chemistry would help solve the controversy regarding the abundances of other molecular species, like HCN, which are under-predicted by XDR models.
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