GLIMPSE Extended Green Objects and the Early Stages of Massive Star Formation

Large-scale Spitzer surveys of the Galactic plane have yielded a new tracer of massive young stellar objects (MYSOs) that are actively accreting and driving outflows: extended emission in the IRAC 4.5 mu m band, believed to arise from shocked molecular gas. The GLIMPSE catalog of extended 4.5 mu m sources (called EGOs, Extended Green Objects, for the common coding of 3-color IRAC images) is a unique sample, well-suited for studying the initial stages of massive star formation and establishing an observation-based MYSO evolutionary sequence. In this proceeding, we present results from extensive recent high-resolution Sub-millimeter Array (SMA) and Very Large Array (VLA) observations of EGOs at cm-mm wavelengths, including maser, molecular line, and continuum studies. These observations often reveal (proto) clusters that exhibit chemical and evolutionary diversity.