詹姆斯·韦布空间望远镜观测到的猎户座棒、NGC7023 和马头星云中的 H2 发射
H2 emission in the Orion Bar, NGC7023 and the Horsehead Nebula observed with the James Webb Space Telescope
- Instituto de Física Fundamental (CSIC)（基础物理研究所（西班牙科学理事会））
- Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS（空间天体物理学研究所，巴黎萨克雷大学，法国国家科学研究中心）
- Department of Physics and Astronomy, University of Western Ontario（韦仕敦大学物理与天文系）
- Institute for Earth and Space Exploration, The University of Western Ontario（韦仕敦大学地球与太空探索研究所）
- Department of Astronomy, University of Michigan（密歇根大学天文系）
- Astronomy Department, University of Maryland（马里兰大学天文系）
- Leiden Observatory, Leiden University（莱顿大学莱顿天文台）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用JWST观测猎户座棒、NGC7023和马头星云的H2发射，分析其空间形态与激发机制，发现不同PDR中温度相似但正仲比有差异，并指出H2发射不足以单独示踪PDR内部温度密度梯度，需结合其他示踪剂。
AI中文摘要：
分子氢（H2）是星际介质中最丰富的分子，是研究光致离解区（PDR）的便捷工具。詹姆斯·韦布空间望远镜（JWST）凭借其高空间分辨率、高灵敏度和波长覆盖范围，为探测 H2 转动线和振转线及其空间形态提供了独特的途径。我们的目标是分析在多个 PDR（猎户座棒、NGC7023 和马头星云）中利用 JWST 探测到的 H2 线发射，以约束离解前缘的物理结构，并比较不同区域中紫外辐射场和气体密度的影响。对 H2 空间形态的分析显示，所有区域均存在相似的丝状结构。观测到 H2 线之间的空间偏移（0.5 角秒），这与激发机制（热化线 vs FUV 泵浦线）的差异以及温度梯度有关。尽管入射辐照条件不同，但对 H2 转动激发的分析得出三个 PDR 中相似的高气体温度。这对于某一类受激发的 PDR（如猎户座棒和 NGC7023）是预期的，因为其离解前缘处的 G0 和密度相似。然而，对于像马头星云这样激发较弱的 PDR，这一结果令人意外。三个 PDR 中转动能级和振转能级的正仲比（OPR）存在差异。我们还利用 H2 振转线和 0-0 S(3) 线估算了视场内的视觉消光，得到了显著不同的结果，这些结果同时约束了几何形状和尘埃颗粒组成。由于复杂的三维几何结构，H2 发射在整个视场中均可观测到，且主要由薄的紫外照射层主导，这使得 H2 无法作为 PDR 更深、更冷分子层中气体温度的可靠示踪剂。因此，H2 发射不足以示踪 PDR 中可能的温度和密度梯度，必须与其他示踪剂结合使用。
英文摘要：
Molecular hydrogen (H2), the most abundant molecule in the interstellar medium, is a handy tool to study Photodissociation Regions. The JWST, with its high spatial resolution, sensitivity, and wavelength coverage, provides unique access to the detection and spatial morphology of the H2 rotational and rovibrational lines. Our goal is to analyze H2 line emission detected with JWST in several PDRs (the Orion Bar, NGC7023, and the Horsehead Nebula) to constrain the physical structure of dissociation front, and compare the impact of the ultraviolet field and the gas density across different regions. The analysis of H2 spatial morphology reveals similar filamentary structures across all regions. Spatial shifts between H2 lines (0.5") are observed and linked to differences in excitation mechanisms (thermalized vs FUV-pumped lines) and the temperature gradient. Despite differences in incident irradiation conditions, analysis of H2 rotational excitation yields high gas temperatures that are similar across the three PDRs. This is expected for a certain regime of excited PDRs (such as Orion and NGC7023), where the G0 at the DFs and the density are similar. However, it is surprising for less excited PDRs like the Horsehead Nebula. OPRs in the rotational and rovibrational levels differ across the three PDRs. We also used H2 rovibrational lines and the 0-0 S(3) line to estimate the visual extinction across the field of view, yielding markedly different results that constrain both the geometry and the grain composition. Due to the complex 3D geometry, H2 emission is observed throughout the FOV and is dominated by the thin UV illuminated layer, making H2 an unreliable tracer of gas temperature in deeper and coolers molecular layers of the PDR. Therefore, H2 emission is not sufficient to trace the possible temperature and density gradient across PDRs and must therefore be associated with other tracers.
