[论文解读] ATLASGAL-selected massive clumps in the inner Galaxy: V. Temperature structure and evolution

A. Giannetti, S. Leurini+6 more|Repository of the Academy's Library (Library of the Hungarian Academy of Sciences)|Mar 24, 2017

Astrophysics and Star Formation Studies参考文献 87被引用 25

一句话总结

本研究利用ATLASGAL、ALMA及地面毫米/亚毫米波观测，调查了银河系内侧大质量团块的温度结构与演化序列。基于L/M比值与红外/射电连续成分的统计分析，确定了一条有效的演化序列，揭示了气体逐步变暖、线宽增加及H₂体密度上升的过程，其不同阶段分别对应吸积、主序星穿越与反馈主导阶段。

ABSTRACT

(Abridged) Aims: We aim to use the progressive heating of the gas caused by the feedback of high-mass young stellar objects (YSOs) to prove the statistical validity of the most common schemes used to define an evolutionary sequence for high-mass clumps, and characterise the sensitivity of different tracers to this process. Methods: From the spectroscopic follow-ups of the ATLASGAL TOP100 sample, we selected several multiplets of CH3CN, CH3CCH, and CH3OH emission lines to derive and compare the physical properties of the gas in the clumps along the evolutionary sequence. Our findings are compared with results obtained from CO isotopologues, dust, and NH3 from previous studies on the same sample. Results: The chemical properties of each species have a major role on the measured physical properties. Low temperatures are traced by NH3, CH3OH, and CO (in the early phases), the warm and dense envelope can be probed with CH3CN, CH3CCH, and, in evolved sources via CO isotopologues. CH3OH and CH3CN are also abundant in the hot cores, and their high-excitation transitions may be good tools to study the kinematics in the hot gas surrounding the YSOs that these clumps are hosting. All tracers show, to different degrees, progressive warming with evolution. The relation between gas temperature and L/M is reproduced by a toy model of a spherical, internally heated clump. Conclusions: The evolutionary sequence defined for the clumps is statistically valid and we could identify the processes dominating in different intervals of L/M. For L/M<2Lsun/Msun a large quantity of gas is still being accumulated and compressed at the bottom of the potential well. Between 2Lsun/Msun40Lsun/Msun HII regions become common, showing that dissipation of the parental clump dominates.

研究动机与目标

• 理解银河系内侧大质量团块的温度结构与演化过程。
• 确定L/M比值与红外/射电连续成分是否能定义一条统计上有效的演化序列。
• 将观测到的分子谱线性质（如CH₃CN、CH₃OH）与物理条件及演化阶段关联。
• 评估观测到的丰度是否与Garrod等（2008）的化学模型在不同气体相中保持一致。
• 建立一个基于多波段数据的高质​​量恒星形成区演化阶段分类框架。

提出的方法

• 利用ATLASGAL 870 μm连续成分数据，从银河系内侧筛选大质量团块。
• 结合ALMA及地面观测（Mopra、IRAM 30m）的分子谱线（CH₃CN、CH₃OH、CO），探测气体温度与运动学特性。
• 通过乙腈的高J与高K跃迁及扭转折跃迁甲醇谱线分析激发条件。
• 基于L/M比值与红外/射电连续成分对源进行分类，以定义演化阶段。
• 将观测到的分子丰度与Garrod等（2008）化学模型预测值对比，测试完整与简化冰丰度情景。
• 通过统计分析验证演化序列，考察线宽、体密度与脉泽探测率的趋势。

实验结果

研究问题

• RQ1 L/M比值与红外/射电连续成分形态是否能定义大质量团块中一条统计上有效的演化序列？
• RQ2 随着L/M比值与源年龄增加，分子谱线性质（如CH₃CN、CH₃OH）如何演化？
• RQ3 观测到的CH₃CN与CH₃OH丰度在多大程度上与化学模型预测一致？
• RQ4 在演化序列中，物理条件（如气体温度、H₂密度、线宽）发生何种变化？
• RQ5 在何种L/M阈值下，反馈过程占据主导，且紧凑H II区可被探测到？

主要发现

• L/M比值与红外/射电连续成分可定义大质量团块中一条统计上有效的演化序列。
• 当L/M ≤ 2 L☉ M☉⁻¹时，源处于早期坍缩/压缩阶段，CH₃CN检测率低，CO激发处于亚热平衡状态，甲醇脉泽比例仅为17%。
• 在L/M介于2至40 L☉ M☉⁻¹之间时，源经历质量吸积，达到主序星状态（约10 L☉ M☉⁻¹），脉泽比例由33%上升至80%，热核心活动增强。
• 当L/M ≥ 40 L☉ M☉⁻¹时，射电连续成分变得普遍，表明反馈占主导，脉泽检测率稳定在约80%。
• 热核心中CH₃CN丰度（约4×10⁻¹⁰）与包层中（约10⁻⁷）均与Garrod等（2008）模型一致。
• 仅当采用简化冰丰度模型时，热气体中CH₃OH丰度才与模型预测一致；冷气体中CH₃OH丰度显著高于预测值。