A Class I and Class II Methanol Maser Survey of Extended Green Objects
  (EGOs) from the GLIMPSE Survey
  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.
