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Wednesday 06 Jul 2011: Early Stages of Massive Star Formation: Extended Green Objects (EGOs) from the GLIMPSE Survey
Claudia Cyganowski -
Physics, 4th floor 11:00-11:30
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, or “green fuzzies,” for the common coding of the [4.5] band as green in 3-color IRAC images) and the evidence that EGOs, as a population, are massive YSOs. I will present the results of high-resolution VLA 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 in 3.6 cm and 1.3 cm continuum emission, which trace ionized gas. Weak or absent cm-wavelength continuum emission indicates that these EGOs are young (proto)stars. High detection rates of 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 that 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. One of the EGOs studied is associated with at least three compact cores, and is likely a protocluster. The outflow driving sources are compact mm continuum cores that exhibit hot-core spectral line emission. I will present initial results from an EVLA survey in diagnostic cm-wavelength lines (ammonia, methanol) using the new WIDAR correlator, and discuss evidence for chemical and evolutionary diversity within the EGO sample revealed by the EVLA and mm data.
