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Chemical features in the circumnuclear disk of the Galactic center

机译：银河系中心周核盘的化学特征

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Aims. The circumnuclear disk (CND) of the Galactic center is exposed to many energetic phenomena coming from the supermassive black hole Sgr A* and from stellar activities. These energetic activities can affect the chemical composition in the CND through interaction with UV photons, cosmic rays, X-rays, and shock waves. We aim to constrain the physical conditions present in the CND through chemical modeling of observed molecular species detected toward it. Methods. We analyzed a selected set of molecular line data taken toward a position in the southwest lobe of the CND with the IRAM 30m and APEX 12-m telescopes and derived the column density of each molecule via a large velocity gradient (LVG) analysis. The determined chemical composition is compared with a time-dependent, gas-grain chemical model based on the UCL_CHEM code,which includes the effects of shock waves with varying physical parameters. Results. We detect molecules, such as CO, HCN, HCO+, HNC, CS, SO, SiO, NO, CN, H2CO, HC3N, N2H+, and H3O+, and obtain their column densities. Total hydrogen densities obtained from LVG analysis range between 2 × 104 and 1 × 106cm-3 and most species indicate values around several × 105cm-3. These values are lower than those corresponding to the Roche limit, which shows that the CND is tidally unstable. The chemical models show good agreement with the observations in cases where the density is ~104cm-3, the cosmic-ray ionization rate is high, > 10-15s-1, or shocks with velocities > 40 km?s-1 have occurred. Conclusions. Comparison of models and observations favors a scenario where the cosmic-ray ionization rate in the CND is high, but precise effects of other factors, such as shocks, density structures, UV photons, and X-rays from the Sgr A*, must be examined with higher spatial resolution data.
机译：目的银河系中心的圆核盘（CND）暴露于来自超大质量黑洞Sgr A *和恒星活动的许多高能现象。这些高能活动可以通过与紫外线光子，宇宙射线，X射线和冲击波的相互作用来影响CND中的化学成分。我们旨在通过对观察到的分子种类进行化学建模来限制CND中存在的物理条件。方法。我们使用IRAM 30m和APEX 12-m望远镜分析了在CND西南瓣位置获取的分子线数据集，并通过大速度梯度（LVG）分析得出了每个分子的柱密度。将确定的化学成分与基于UCL_CHEM代码的随时间变化的气粒化学模型进行比较，该模型包括具有变化的物理参数的冲击波的影响。结果。我们检测分子，例如CO，HCN，HCO +，HNC，CS，SO，SiO，NO，CN，H2CO，HC3N，N2H +和H3O +，并获得其列密度。从LVG分析获得的总氢密度范围为2×104至1×106cm-3，大多数物种的指示值约为数×105cm-3。这些值低于对应于罗氏极限的值，这表明CND在潮汐上不稳定。在密度为〜104cm-3，宇宙射线电离率高，> 10-15s-1或发生速度> 40 km？s-1的冲击的情况下，化学模型与观测值显示出良好的一致性。结论。模型和观测值的比较有利于CND中宇宙射线电离率很高的情况，但是必须严格考虑其他因素的精确影响，例如冲击，密度结构，UV光子和来自Sgr A *的X射线。用更高的空间分辨率数据进行检查。

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