高质量恒星形成初期的运动学和热结构
Kinematic and Thermal Structure at the onset of high-mass star formation
摘要：
我们希望了解年轻的大质量气体团在大质量恒星形成之前和最早的演化阶段的运动学和热特性。我们找到引力坍缩的迹象了吗？我们是否在红外辐射源附近发现了温度梯度？我们是否在稠密而寒冷的气体团的中心发现了相干的速度结构？为了确定运动学和气体温度，我们使用了氨，因为众所周知，氨是致密气体的良好示踪剂和温度计。我们用VLA和Effelsberg 100米望远镜观测了7个非常年轻的大质量恒星形成区的NH $_3$（1，1）和（2，2）谱线。这使我们能够研究速度结构，线宽，和气体温度在3-5 $"$的高空间分辨率，对应于$\sim$ 0.05 pc。我们发现平均温度在10 K到30 K之间的冷气体团簇。观测结果没有揭示红外发射峰和氨温度峰之间的明确相关性。我们报告的$\sim$ 1.3公里秒$^{-1}$的线宽的上限，在我们的VLA观测的光谱分辨率极限。这表明在观测尺度上湍流水平相对较低。几乎所有区域都存在速度梯度，典型速度差为1至2 km s $^{-1}$，梯度为5至10 km s $^{-1}$ pc $^{-1}$。这些速度梯度在大多数情况下是平滑的，但有一个例外的源（ISOSS 23053），我们发现几个速度分量与陡峭的速度梯度对团块中心大于30公里秒$^{-1}$个人电脑$^{-1}$。这种陡峭的速度梯度与最近的云塌缩模型相一致。此外，我们报告了氨和冷尘的空间相关性，但我们也发现减少氨排放接近红外发射源。
英文摘要：
We want to understand the kinematic and thermal properties of young massive gas clumps prior to and at the earliest evolutionary stages of high-mass star formation. Do we find signatures of gravitational collapse? Do we find temperature gradients in the vicinity or absence of infrared emission sources? Do we find coherent velocity structures toward the center of the dense and cold gas clumps? To determine kinematics and gas temperatures, we used ammonia, because it is known to be a good tracer and thermometer of dense gas. We observed the NH$_3$(1,1) and (2,2) lines within seven very young high-mass star-forming regions with the VLA and the Effelsberg 100m telescope. This allows us to study velocity structures, linewidths, and gas temperatures at high spatial resolution of 3-5$"$, corresponding to $\sim$0.05 pc. We find on average cold gas clumps with temperatures in the range between 10 K and 30 K. The observations do not reveal a clear correlation between infrared emission peaks and ammonia temperature peaks. We report an upper limit for the linewidth of $\sim$1.3 km s$^{-1}$, at the spectral resolution limit of our VLA observation. This indicates a relatively low level of turbulence on the scale of the observations. Velocity gradients are present in almost all regions with typical velocity differences of 1 to 2 km s$^{-1}$ and gradients of 5 to 10 km s$^{-1}$ pc$^{-1}$. These velocity gradients are smooth in most cases, but there is one exceptional source (ISOSS23053), for which we find several velocity components with a steep velocity gradient toward the clump centers that is larger than 30 km s$^{-1}$ pc$^{-1}$. This steep velocity gradient is consistent with recent models of cloud collapse. Furthermore, we report a spatial correlation of ammonia and cold dust, but we also find decreasing ammonia emission close to infrared emission sources.
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