活跃恒星形成核样本中的含硫分子
Sulfur-bearing molecules in a sample of active star-forming cores
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中文总结 AI 辅助
本研究通过ALMA观测16个演化恒星形成核，发现含硫分子丰度较早期核更高，SO2/SO可作为化学时钟，且核演化导致气体混合消除空间分层。
中文摘要 AI 辅助
涉及硫的天体化学过程尚未被充分理解，因为宇宙中的硫储库以及含硫物种的产生途径仍然难以捉摸。要解决这一问题，需要能够探测单个分子核的高分辨率干涉观测。继我们先前聚焦于早期分子核的研究之后，我们受到激励将这一调查扩展到演化核样本，以理解它们的化学转变。我们分析了ALMA对与甲醇脉泽相关的大质量恒星形成区域中16个分子核的数据，针对了先前工作中对早期分子核研究的相同六种含硫物种：SO、SO2、H2CS、SO+、NS和34SO。柱密度和丰度在假设局部热动平衡（LTE）下导出，温度则根据甲醇跃迁估算。将演化核获得的结果与先前对早期核获得的结果进行了比较。我们发现演化核中含硫分子的丰度高于早期核，证实了气相中硫随时间的普遍富集。虽然丰度在100-220 K范围内增加，但它们与温度的相关性减弱，表明气体运动学在硫化学中变得越来越重要。这种演化转变涉及化学重组，其中SO2变得占主导。我们确认了SO2/SO作为化学时钟的有效性，尽管化学建模揭示了在运动学过程更显著的源中存在差异，即SO2/SO比率的增加更为陡峭。分子物种的线宽分析表明，核演化和运动学导致气体充分混合，抹去了早期阶段不同物种在核中追踪不同层的空间分层。
英文摘要
Astrochemical processes involving sulfur are not yet well understood because cosmic sulfur reservoirs and the production pathways of sulfur-bearing species remain elusive. Addressing this, requires high-resolution interferometric observations capable of probing individual molecular cores. Following our previous study focused on early molecular cores, we are motivated to expand this investigation toward a sample of evolved cores to understand their chemical transition. We analyzed data from ALMA toward 16 molecular cores in massive star-forming regions associated with methanol masers, targeting the same six sulfur-bearing species studied in a previous work toward early molecular cores: SO, SO2, H2CS, SO+, NS, and 34SO. Column densities and abundances were derived assuming LTE, and temperatures were estimated from methanol transitions. Comparisons were made between the results obtained for the evolved cores and those previously obtained for the early ones. We find that the abundances of the sulfur-bearing molecules are higher in the evolved cores than in the early ones, confirming a general time-dependent enrichment of sulfur in the gas phase. While abundances increase within the 100-220 K range, their correlation with temperature weakens, suggesting that gas kinematics become increasingly more important in the sulfur chemistry. This evolutionary transition involves a chemical reorganization where SO2 becomes dominant. We confirm the validity of SO2/SO as a chemical clock, though chemical modeling reveals a discrepancy in sources with more pronounced kinematic processes, namely a steeper increase in the SO2/SO ratio. The line-width analysis of the molecular species indicates that core evolution and kinematics lead to a well-mixed gas, erasing the spatial stratification where different species trace distinct layers in the cores at earlier stages.
发表机构
- CONICET - Universidad Nacional de Salta（阿根廷国家科学研究委员会 - 萨尔塔国立大学）
- Universidad Nacional de Salta（萨尔塔国立大学）
- Universidad de Buenos Aires（布宜诺斯艾利斯大学）
- CONICET - Universidad de Buenos Aires（阿根廷国家科学研究委员会 - 布宜诺斯艾利斯大学）
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