[论文解读] Multi-frequency mapping of the S255IR region at a wavelength of 1~mm

E. A. Mikheeva, S. V. Kalenskii+3 more|arXiv (Cornell University)|Feb 16, 2026

Astrophysics and Star Formation Studies被引用 0

一句话总结

该论文在S255IR星形成区进行210–250 GHz的SMA干涉映射，分析SMA1/SMA2核心的光谱，检测到53种分子（包括COMs），估计温度与光学深度，并讨论可能与喷流相关的环状腔壁结构。

ABSTRACT

The results of interferometric observations of the star-forming region S255IR in the frequency range 210--250 GHz are presented. The observations were carried out with the antenna array SMA (Hawaii, USA). Fifty-three molecules were detected, including complex organic molecules (COMs) such as CH$_3$CHO, CH$_3$CN, CH$_3$CH$_2$CN, and many others. Typical rotational temperatures in the hot core SMA1 fall in the range 100--200 K. Optical depths in the lines of methanol and some other molecules in the cores SMA1 and SMA2 were estimated. In SMA1, the optical depth of one of the strongest methanol lines, $5_{-1}-4_{-1}E$, proved to be $23.8 \pm 1.5$. Based on this value, one can assume that the lines of other oxygen-containing COMs, such as CH$_3$OCHO, CH$_3$OCH$_3$, CH$_3$CH$_2$OH, which are typically much less abundant in hot cores than methanol, are optically thin in SMA1. Most of the detected molecules can be roughly divided into two groups. The molecules of the first group emit exclusively toward the hot core SMA1, while some or all lines of the molecules of the second group, in addition to SMA1, can be seen toward a ring-like structure to the west of SMA1. This structure is most likely associated with the walls of a cavity formed by high-velocity outflows driven by young stellar objects (YSOs) in molecular cores SMA1, SMA2, and possibly SMA3. The gas temperature and density in the cavity walls were estimated using methanol lines. The temperature was found to be about 50--60 K, and the density about $10^7-10^8$ cm$^{-3}$. The column density of methanol near the brightness peaks in the lines of this molecule is about $5 imes 10^{15}$~cm$^{-2}$. The column densities of other COMs in the ring-like structure will be determined in future studies with increased sensitivity achieved by spectral line stacking.

研究动机与目标

• 研究S255IR区域内不同分子（尤其是COMs）的空间分布。
• 表征热核SMA1及周围结构的物理条件（温度、密度）。
• 识别并绘制分子谱线，以理解区域的星际化学复杂性及与喷流相关的特征。

提出的方法

• 在210–250 GHz带进行SMA干涉观测，分辨率为4''。
• 为24个谱窗构建光谱数据立方体，并利用Lovas/NIST目录鉴定线。
• 绘制所选分子线的积分强度图与通道图。
• 分析转动图以在LTE假设下推导转动温度与柱密度。
• 利用同位素比估计若干分子（如CH3OH、H2CO、CS、SO、OCS）的光学深度。
• 解释空间分布以区分SMA1的发射与来自环状腔壁之类的扩展结构的发射。

Figure 1: Map of the S255IR region in the $5_{0}-4_{0}A^{+}$ methanol line at a frequency of 241791.367 MHz. Triangular markers indicate the dense cores SMA1 (coincident with NIRS3), SMA2, and SMA3 (coincident with NIRS1)

实验结果

研究问题

• RQ1 SMA1、SMA2及其周围区域中COMs及其他分子的空间分布如何？
• RQ2 基于LTE转动图，SMA1中检测到的分子转动温度与柱密度是多少？
• RQ3 是否存在与喷流相关的环状腔壁结构及其物理性质（温度、密度）？
• RQ4 关键分子线的光学深度如何，同位素分析对其有何约束？
• RQ5 分子发射如何区分热核（SMA1）与邻近区域或腔体？

主要发现

• 检测到53种分子，包括COMs，如CH3CHO、CH3CN、CH3CH2CN、CH3OCHO、CH3OCH3、CH3CH2OH。
• SMA1热核的转动温度一般在100–200 K范围（部分物种温度更高）。
• 甲醇及多条线的光学深度估计显示甲醇线可能极厚（如5−1−4−1E τ≈23.8）。
• 两类分子呈现不同的空间行为：I组主要发射于SMA1；II组在SMA1与一个西向环状/腔壁结构处发射，可能与喷流壁相关，气体温度约50–60 K，密度在10^7–10^8 cm^−3。
• CN映射揭示直径约15''的环状结构， brightest peak在SMA2对侧，提示腔壁起源。
• 指向SMA1的若干物种柱密度包括：HNCO ≈7.4×10^14 cm^−2、CH3OH ≈4.7×10^16 cm^−2、CH3CN ≈5.9×10^14 cm^−2、CH3CHO ≈1.6×10^15 cm^−2。

Figure 2: Spectrum toward SMA1