The diversity of methanol maser morphologies from VLBI observations
The diversity of methanol maser morphologies from VLBI observations
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DOI：
10.1051/0004-6361/200912250
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发表时间：
2009-05
影响因子：
6.5
通讯作者：
A. Bartkiewicz;M. Szymczak;H. Langevelde;A. Richards;Y. C. F. Astronomy;N. C. University;Poland Joint Instit
中科院分区：
文献类型：
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作者：
A. Bartkiewicz;M. Szymczak;H. Langevelde;A. Richards;Y. C. F. Astronomy;N. C. University;Poland Joint Instit
上下文6.7千兆赫的甲醇脉泽标志着高质量星星形成的早期阶段，但这个脉泽的起源目前是一个有争议的问题。特别是，尚不清楚脉泽发射是否出现在圆盘、外流或冲击后面，进入旋转的分子云。目标。我们调查了结构的甲醇脉泽跟踪环境中的高质量的原恒星候选人通过观察一个均匀的样品中选择的甲醇脉泽托伦调查。我们还通过寻找相关的H II区域和IR发射来探索它们的起源。方法.我们选择了30个甲醇源，使用MERLIN和另外3个文献中实现了改进的位置精度。我们使用欧洲VLBI网络的扩展望远镜阵列与5厘米（6 GHz）接收器对其中31个进行了成像。我们使用VLA搜索8.4 GHz无线电连续谱对应物，并检查了档案中3.6-8 μm的Spitzer GLIMPSE数据。结果高角分辨率图像使我们能够非常详细地分析甲醇脉泽的形态和运动学，并验证它们与射电连续谱和中红外发射的关联。在恒星形成区，一种新的“环状”甲醇脉泽出现得惊人地普遍，占样本的29%。结论.这种新的形态强烈地表明，甲醇脉泽起源于原恒星或年轻的大质量星星周围的圆盘或环面。然而，脉泽运动学表明，强烈的影响流出或落入。这表明它们形成在盘/环面和流之间的界面处。斯皮策的结果也有力地支持了这一点，因为大多数脉泽与4.5 μm辐射的一致性小于1 μ m。只有四个脉泽与UC H II区的中心部分有关。这意味着6.7GHz甲醇脉泽发射发生在cm波段可观测到的H Ⅱ区形成之前。
Context. The 6.7 GHz methanol maser marks an early stage of high-mass star formation, but the origin of this maser is currently a matter of debate. In particular it is unclear whether the maser emission arises in discs, outflows or behind shocks running into rotating molecular clouds. Aims. We investigated which structures the methanol masers trace in the environment of high-mass protostar candidates by observing a homogenous sample of methanol masers selected from Torun surveys. We also probed their origins by looking for associated H II regions and IR emission. Methods. We selected 30 methanol sources with improved position accuracies achieved using MERLIN and another 3 from the literature. We imaged 31 of these using the European VLBI Network’s expanded array of telescopes with 5-cm (6-GHz) receivers. We used the VLA to search for 8.4 GHz radio continuum counterparts and inspected Spitzer GLIMPSE data at 3.6–8 μm from the archive. Results. High angular resolution images allowed us to analyze the morphology and kinematics of the methanol masers in great detail and verify their association with radio continuum and mid-infrared emission. A new class of “ring-like” methanol masers in starforming regions appeared to be suprisingly common, 29% of the sample. Conclusions. The new morphology strongly suggests that methanol masers originate in the disc or torus around a proto- or a young massive star. However, the maser kinematics indicate the strong influence of outflow or infall. This suggests that they form at the interface between the disc/torus and a flow. This is also strongly supported by Spitzer results because the majority of the masers coincide with 4.5 μm emission to within less than 1 �� . Only four masers are associated with the central parts of UC H II regions. This implies that 6.7 GHz methanol maser emission occurs before H II region observable at cm wavelengths is formed.