从GLIMPSE巡天得到的扩展绿天体（EGO）的I类和II类甲醇脉泽巡天
A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
摘要：
我们提出了一个高角分辨率甚大阵（VLA）的I类44 GHz和II类6.7 GHz的甲醇脉泽调查的样本的20个大质量的年轻恒星对象（MYSO）流出的候选人的基础上选择的扩展4.5微米发射的斯皮策银河遗产红外中面调查非凡（GLIMPSE）图像。这些4.5微米选择的候选者被称为扩展绿色物体（EGO），因为在三色IRAC图像中该波段的共同编码为绿色。6.7 GHz的II类甲醇脉泽，这是专门与大规模的YSO，对EGO的检测率大于~64%-近两倍的检测率使用其他MYSO选择标准的调查。44 GHz甲醇脉泽的探测率约为89%，而6.7 GHz甲醇脉泽的探测率为89%。这两种类型的甲醇脉泽具有不同的空间分布：6.7 GHz脉泽集中在中心，通常与24微米发射相一致，而44 GHz脉泽分布广泛，通常跟踪扩散的4.5微米特征。我们还介绍了一个互补的詹姆斯克拉克麦克斯韦望远镜（JCMT）单点分子线调查的EGO流出示踪剂HCO+（3-2）和SiO（5-4）的结果。HCO+线轮廓和高SiO检测率（90%）表明存在活跃的外流。没有44 GHz的连续发射检测到在5毫焦耳/束（5西格玛）的水平对95%的EGO调查，不包括明亮的超紧凑HII区域作为4.5微米流出的动力源。我们的调查结果构成了强有力的证据，表明EGO是年轻的，大规模的YSO，具有活跃的外流，大概是由持续的吸积提供动力。
英文摘要：
We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz methanol maser survey of a sample of ~20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 micron emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) images. These 4.5 micron-selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color IRAC images. The detection rate of 6.7 GHz Class II methanol masers, which are associated exclusively with massive YSOs, towards EGOs is greater than ~64%--nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz methanol masers, which trace molecular outflows, is ~89% towards EGOs associated with 6.7 GHz methanol masers. The two types of methanol masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 micron emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 micron features. We also present results of a complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular line survey of EGOs in the outflow tracers HCO+(3-2) and SiO(5-4). The HCO+ line profiles and high SiO detection rate (90%) are indicative of the presence of active outflows. No 44 GHz continuum emission is detected at the 5 mJy/beam (5 sigma) level towards 95% of EGOs surveyed, excluding bright ultracompact HII regions as powering sources for the 4.5 micron outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.
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