A SEARCH FOR INFALL EVIDENCE IN EGOs. I. THE NORTHERN SAMPLE
A SEARCH FOR INFALL EVIDENCE IN EGOs. I. THE NORTHERN SAMPLE
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DOI：
10.1088/0004-637x/710/1/150
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发表时间：
2009-12
期刊：
影响因子：
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通讯作者：
Xi Chen;Zhi-qiang Shen;Jingjing Li;Ye Xu;Jinhua He
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作者：
Xi Chen;Zhi-qiang Shen;Jingjing Li;Ye Xu;Jinhua He
我们报告了第一个系统的调查分子线（包括HCO+（1-0）和12 CO，13 CO，C18 O（3毫米波段的1-0线）朝向与持续外流相关的88个大质量年轻恒星天体（MYSO）候选者的新样本（称为扩展绿色对象或EGO）在北方半球用紫金山天文台13.7米射电望远镜进行的斯皮策GLIMPSE巡天观测中发现了这一点。通过分析72个具有HCO+检测的EGO中的69个的光学粗线HCO+的不对称性，我们发现29个具有“蓝色不对称轮廓”的源和19个具有“红色不对称轮廓”的源。这导致0.14的蓝色过量，被视为所观察到的EGO样品中的塌缩核心的特征。我们发现，与红外暗云（IRDC）无关的源显示出比与IRDC相关的源（-0.08）更高的蓝色过量（0.41），并且“可能的”流出候选者显示出比“可能的”流出候选者（0.05）更高的蓝色过量（0.29）。一个更高的蓝色过剩（0.19）和更低的蓝色过剩（0.07），也测得在超紧凑H II区域和6.7 GHz的II类甲醇脉泽源，分别。这表明，在我们的完整样本中，相对较小的蓝色过量（0.14）是由于这样一个事实，即观察到的EGO主要是由流出，并在早期的演变阶段与IRDC和6.7 GHz甲醇脉泽。由CO谱线导出的EGO周围的云的物理性质与大质量团块的物理性质相似，其中可能嵌入了与EGO相关的大质量恒星形成核心。从20个可能的陨石坑中得出的陨石坑速度和质量陨石坑率也与多年期SO观测中发现的典型值一致。因此，我们的观察结果进一步支持Cyganowski等人的推测。从统计学的角度来看，EGO跟踪人口与持续的外流活动，并在大规模原恒星演化的活跃快速吸积阶段，虽然可能有限制，由于单点调查与大光束。
We report the first systematic survey of molecular lines (including HCO+ (1–0) and 12CO, 13CO, C18O (1–0) lines at the 3 mm band) toward a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the Purple Mountain Observatory 13.7 m radio telescope. By analyzing the asymmetries of the optically thick line HCO+ for 69 of 72 EGOs with HCO+ detection, we found 29 sources with “blue asymmetric profiles” and 19 sources with “red asymmetric profiles.” This results in a blue excess of 0.14, seen as a signature of collapsing cores in the observed EGO sample. We found that the sources not associated with infrared dark clouds (IRDCs) show a higher blue excess (0.41) than those associated with IRDCs (−0.08), and “possible” outflow candidates show a higher blue excess (0.29) than “likely” outflow candidates (0.05). A higher blue excess (0.19) and a lower blue excess (0.07) were also measured in ultracompact H ii regions and 6.7 GHz class II methanol maser sources, respectively. These suggest that the relatively small blue excess (0.14) in our full sample is due to the fact that the observed EGOs are mostly dominated by outflows and at an earlier evolutionary phase associated with IRDCs and 6.7 GHz methanol masers. The physical properties of clouds surrounding EGOs derived from CO lines are similar to those of massive clumps wherein the massive star-forming cores associated with EGOs possibly embedded. The infall velocities and mass infall rates derived for 20 infall candidates are also consistent with the typical values found in MYSOs. Thus, our observations further support the speculation of Cyganowski et al. that EGOs trace a population with ongoing outflow activity and at the active rapid accretion stage of massive protostellar evolution from a statistical view, although there may be limitations due to a single-pointing survey with a large beam.