2009ApJ...702.1615C

We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz CH₃ OH maser survey of a sample of ∼20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 µm emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire images. These 4.5 µm selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color Infrared Array Camera images. The detection rate of 6.7 GHz Class II CH₃ OH masers, which are associated exclusively with massive YSOs, toward EGOs is ≳ 64%–nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz CH₃ OH masers, which trace molecular outflows, is ∼89% toward EGOs associated with 6.7 GHz CH₃ OH masers. The two types of CH₃OH masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 µm emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 µm 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 (5σ) level toward 95% of EGOs surveyed, excluding bright ultracompact H II regions as powering sources for the 4.5 µm outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.