| Abstract |
A promising new diagnostic for identifying actively accreting massive
young stellar objects (MYSOs) has emerged from large-scale Spitzer
surveys of the Galactic plane: extended emission in the IRAC 4.5 micron
band, believed to trace shocked molecular gas in active protostellar
outflows. I will discuss the GLIMPSE catalog of extended 4.5 micron
sources (called EGOs, Extended Green Objects, for the common coding of
the [4.5] band as green in 3-color composite IRAC images) and the
evidence that EGOs, as a population, are massive YSOs. I will present
the results of high-resolution EVLA surveys of 20 EGOS in the 6.7 GHz
Class II and 44 GHz Class I methanol maser transitions, which
respectively trace high-mass protostars and molecular outflows, and a
JCMT survey in the molecular outflow tracers HCO+ and SiO. High
detection rates of all outflow tracers and the spatial distribution of
the masers with respect to the midinfrared emission provide convincing
evidence that the surveyed EGOs are much-sought MYSOs which are actively
accreting and driving outflows. I complement the survey results with
detailed case studies of two EGOs using SMA and CARMA data. The
high-resolution mm observations reveal bipolar molecular outflows
coincident with the 4.5 micron lobes in both sources. Strong SiO(2-1)
emission is also detected, confirming that the extended 4.5 micron
emission traces recently shocked gas in active outflows. While a single
dominant outflow is identified in each of the studied EGOs, the mm data
show that one of the EGOs is associated with at least three compact
cores, and may be a protocluster.
Support for this work was provided by NSF grant AST-0808119, by a NRAO
Graduate Summer Student Research Assistantship to C. Cyganowski, and by
a NSF Graduate Research Fellowship to C. Cyganowski. |