Molecular shock tracers in NGC 1068: SiO and HNCO
Molecular shock tracers in NGC 1068: SiO and HNCO
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DOI：
10.1051/0004-6361/201628946
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发表时间：
2016-09
期刊：
影响因子：
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通讯作者：
G. Kelly;S. Viti;S. Garc'ia-Burillo;A. Fuente;A. Usero;M. Krips;R. Neri
中科院分区：
文献类型：
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作者：
G. Kelly;S. Viti;S. Garc'ia-Burillo;A. Fuente;A. Usero;M. Krips;R. Neri
SiO(3-2) 和 HNCO(6-5) 发射已在 NGC 1068 中使用 Plateau de Bure 干涉仪 (PdBI) 成像。我们执行 LTE 和 RADEX 分析，以确定排放这两条线的气体的柱密度和物理特性。然后，我们使用化学模型来确定排放源。活动星系核以东有一个强烈的 SiO2 峰值，而西方有较弱的探测到。这种分布与 HNCO 的分布形成鲜明对比，后者在西方国家中的检测更为强烈。东部的 SiO 排放峰与 CO 追踪的分子气体质量峰值相似。HNCO 排放与该峰值偏移多达 80 pc ( 1")。我们比较了东部和西部的速度积分线比。我们确认 SiO 排放在东部占主导地位，而在西部则相反。我们使用 RADEX 分析了可能产生这种排放的气体条件。我们发现，在东部和西部，SiO 排放占主导地位。 在西方，我们无法限制气体的单一温度。我们运行了 CND 中潜在冲击过程的化学模型网格，发现 SiO 在快速（60 km/s）冲击期间显着增强，但在慢速（20 km/s）冲击期间没有显着增强，在完全未受到冲击的气体中也没有。我们发现了 HNCO 的反函数，其丰度在缓慢冲击和温暖的非冲击气体中增加。高 SiO2 和低 HNCO 表明 快速冲击，而高 HNCO 和低 SiO 表明缓慢冲击或温暖、致密、非冲击气体。因此，东结很可能含有受到严重冲击的气体。根据化学模型，西结中的气体可能没有受到冲击，或者可能正在经历温和得多的冲击事件。考虑 RADEX 结果时，两种情况中较温和的冲击事件更有可能发生。
SiO(3-2) and HNCO(6-5) emission has been imaged in NGC 1068 with the Plateau de Bure Interferometer (PdBI). We perform an LTE and RADEX analysis to determine the column densities and physical characteristics of the gas emitting these two lines. We then use a chemical model to determine the origin of the emission. There is a strong SiO peak to the East of the AGN, with weak detections to the West. This distribution contrasts that of HNCO, which is detected more strongly to the West. The SiO emission peak in the East is similar to the peak of the molecular gas mass traced by CO. HNCO emission is offset from this peak by as much as 80 pc ( 1"). We compare velocity integrated line ratios in the East and West. We confirm that SiO emission strongly dominates in the East, while the reverse is true in the West. We use RADEX to analyse the possible gas conditions that could produce such emission. We find that, in both East and West, we cannot constrain a single temperature for the gas. We run a grid of chemical models of potential shock processes in the CND and find that SiO is significantly enhanced during a fast (60 km/s) shock but not during a slow (20 km/s) shock, nor in a gas not subjected to shocks at all. We find the inverse for HNCO, whose abundance increases during slow shocks and in warm non-shocked gas. High SiO and low HNCO indicated a fast shock, while high HNCO and low SiO indicates either a slow shock or warm, dense, non-shocked gas. The East Knot is therefore likely to contain gas that is heavily shocked. From chemical modelling, gas in the West Knot may be non-shocked, or maybe undergoing a much milder shock event. When taking into account RADEX results, the milder shock event is the more likely of the two scenarios.