天鹅座全尺度化学与动力学环境巡天：CASCADE。IV. 揭示 DR18 中的隐藏结构
The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. IV. Unveiling the hidden structures in DR18
AI总结：
本研究利用NOEMA与IRAM 30米的3.6 mm观测及多波段归档数据，揭示DR18中B2星、HII区、PDRs、致密核及低速激波与紫外照射共同塑造的隐藏结构。
摘要：
Cygnus-X复合体是一个邻近的大质量恒星形成区，距离为1.4 kpc，包含若干OB星协。作为Cygnus Allscale Survey of Chemistry and Dynamical Environments（CASCADE，天鹅座全尺度化学与动力学环境巡天）项目的一部分，我们利用Northern Extended Millimeter Array（NOEMA，北方扩展毫米波阵列）和Institut de Radioastronomie Millimétrique（IRAM，毫米波射电天文研究所）30米望远镜，对DR18开展了3.6毫米（mm）连续谱和谱线高分辨率观测（约3–4角秒），覆盖若干分子种类。此外，我们还使用多波段归档数据集，对该区域进行综合分析。3.6 mm与6 cm连续谱辐射的比较证实，一颗B2型恒星（DR18-05）塑造了DR18空腔内的彗星状HII区，电离气体朝向OB2星协逸出。另一方面，延展的3.6 mm和6 cm连续谱辐射可能示踪由Cyg OB2星协而非DR18-05的紫外辐射导致的光蒸发电离气体。DR18-05周围的壳层结构表明，光解离区（PDRs）由膨胀的HII区以及来自DR18-05和OB2恒星的光侵蚀形成。我们还识别出18个具有N₂H⁺发射的致密核，其中一半受引力束缚，并且大多位于PDRs后方较冷的区域。SiO发射仅发现于PDRs中，具有窄线宽（0.8–2.0 km s⁻¹）和较低丰度（X(SiO)约5×10⁻¹¹–1×10⁻¹⁰）。通过与紫外照射激波模型比较，我们认为部分环绕HII区的SiO发射来自分子气体区；这些分子气体在穿过n_H约10⁴至10⁵ cm⁻³的介质时，受到约5 km s⁻¹低速激波的边缘压缩，并受到外部紫外辐射（G₀约10²–10³）照射。
英文摘要：
The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations ($\sim$ 3 - 4$''$) toward DR18, covering several molecular species with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. In addition, multi-wavelength archival datasets were used to provide a comprehensive analysis of the region. A comparison of the 3.6mm and 6 cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association, not from DR18-05. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N$_2$H$^+$ emission, half of which are gravitationally bound and mostly located in colder regions behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths ( 0.8 - 2.0 km s$^{-1}$) and lower abundances (X(SiO) $\sim$ 5$\times$10$^{-11}$ - 1$\times$10$^{-10}$). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with $\sim$ 5 km s$^{-1}$, irradiated by external UV radiation (G$_{\rm 0} \sim 10^{2} - 10^{3}$), as they traverse through a medium with $n_{\rm H} \sim 10^{4}$ to 10$^5$ cm$^{-3}$.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
