AI 中文总结
本研究以猎户座 Bar 为对象，利用 JWST 的 NIRSpec 数据研究近红外连续谱，发现其可近似为两个黑体叠加，碳簇 recurrent fluorescence 或为低温成分的起源，还探测到水冰与CO₂冰的吸收特征。
AI 中文摘要
在反射星云、行星状星云及邻近星系等多种天体中，近红外（NIR）区域存在明显的过剩发射，但该过剩发射的空间分布与光谱形状仍知之甚少。我们对近红外连续谱发射进行光谱研究，获取了猎户座 Bar 这一典型光解离区（PDR）中，相对于3.3μm芳香红外带（AIB）的空间分布，旨在表征其光谱形状并探讨起源。我们利用 JWST 的 NIRSpec 积分场单元获取的猎户座 Bar 三维光谱数据，数据来自“PDRs4All”早期释放科学项目。采用 Cloudy 代码估算前景电离气体的贡献并予以扣除，将观测区域划分为9个物理上不同的区域，为每个区域推导平均光谱。这9个区域包括电离气体、原子 PDR 和分子 PDR，在1~4.5μm区域清晰显示出剩余连续谱；波长大于2.7μm的连续谱与3.3μm AIB 相关性良好，而1.2μm连续谱的相关性不显著。我们进一步发现，猎户座 Bar 的近红外连续谱可近似为两个黑体的叠加：低温成分与 AIB 相关性良好，高温成分则不然。平均光谱还显示出3.0μm和4.27μm处的吸收特征，归因于光谱中存在水冰和CO₂冰。我们探讨了近红外连续谱的可能起源，其中碳簇的 recurrent fluorescence 能更好地解释观测到的低温成分；冰物质的存在表明，视线方向上 PDR 更深层的贡献产生了特征性的冰吸收特征。
英文摘要
Conspicuous excess emission is present in the near-infrared (NIR) region in various objects, including reflection nebulae, planetary nebulae, and nearby galaxies. However, the spatial distribution and spectral shape of the excess emission remain poorly understood. We studied the NIR continuum emission spectroscopically and obtained its spatial distribution relative to the aromatic infrared band (AIB) at 3.3um in the Orion Bar prototypical photodissociation region (PDR). We aim to characterize its spectral shape and discuss its origin. We employed 3D spectroscopic data of the Orion Bar taken with the integrated field unit of NIRSpec on JWST from the Early Release Science program "PDRs4All." Contribution from the foreground ionized gas was estimated using the Cloudy code and subtracted. The observed regions were divided into nine physically distinct regions and an average spectrum was derived for each region. The nine regions, including the ionized gas, atomic PDR, and molecular PDR, clearly show remaining continuum in the region 1--4.5um. The continuum at wavelengths longer than 2.7um shows good correlations with the 3.3um AIB, while the correlation of the continuum at 1.2um is not significant. We further find that the NIR continuum in the Orion Bar can be approximated by a summation of two blackbodies. The low-temperature component correlates with the AIB well, while the high-temperature component does not. The average spectra also show absorption features at 3.0 and 4.27um, which are attributed to the presence in the spectra of water ice and CO2 ice. We discuss possible origins of the NIR continuum, among which recurrent fluorescence from carbon clusters better explains the observed low-temperature component. The presence of ice species suggests a contribution from a deeper layer of the PDR along the line of sight producing characteristic ice absorption features.
Comments15 pages, 13 figures. To appear in Astronomy & Astrophysics
