2011ApJ...743...56C

We present the results of deep, high angular resolution Very Large Array surveys for radio continuum emission toward a sample of 14 GLIMPSE Extended Green Objects (EGOs). Identified as massive young stellar object (MYSO) outflow candidates based on their extended 4.5 µm emission in Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz Class II and/or 44 GHz Class I CH₃ OH masers. No continuum is detected at 3.6 or 1.3 cm toward the majority (57%) of our targets (median rms ∼0.03 and 0.25 mJy/beam). Only two EGOs are associated with optically thin emission consistent with ultracompact/compact H II regions. Both of these sources exhibit cm-λ multiplicity, with evidence that one of the less-evolved members may be driving the 4.5 µm outflow. Most of the other cm-λ EGO counterparts are weak ( ≲ 1 mJy), unresolved, undetected at 1.3 cm, and characterized by intermediate spectral indices consistent with hypercompact (HC) H II regions or ionized winds or jets. One EGO centimeter (cm) counterpart, likely an optically thick HC H II region, is detected only at 1.3 cm and is associated with hot core line emission and H₂ O and 6.7 GHz CH₃OH masers. The results of our exceptionally sensitive survey indicate that EGOs signify an early stage of massive star formation, before photoionizing feedback from the central MYSO significantly influences the (proto)cluster environment. Actively driving outflows (and so, presumably, actively accreting), the surveyed EGOs are associated with significant clump-scale gas reservoirs, providing sufficient material for sustained, rapid accretion.