| Description |
Massive star formation remains a poorly understood phenomenon, largelydue to the difficulty of identifying and studying massive youngstellar objects (MYSOs) in the crucial early active accretion andoutflow phase. Large-scale Spitzer surveys of the Galactic Plane haveyielded a promising new sample of young MYSOs with outflows, which arelikely actively accreting: based on their extended 4.5 um emission inSpitzer images, these sources are known as Extended Green Objects(EGOs) from the common coding of three-color IRAC images. Extensiveground-based follow up observations revealed that the EGOs are indeedrelated to massive outflows from young systems with very highaccretion rates (10^-3 Msun/year). They also revealed a wide varietyof properties: some MYSOs appear in clusters, others are isolated,some are molecular line rich, others not. To test the hypothesis thatthese differences reflect evolutionary effects, we propose SPIRE/FTSand HIFI observations of 4 EGOs. SPIRE/FTS spectra of the 12CO and13CO rotational ladders and HIFI spectra of selected CO line profileswould yield shock-excited gas temperatures and masses, constrainingthe current outflow (and thus accretion) activity in a more direct waythan is possible in low excitation tracers with ground-basedtelescopes. HIFI observations of H2O and NH3 line profiles andabundances would provide independent present day outflow activityindicators and records of the shock history, as these species areformed above temperatures of 230 and 4000 K, respectively, andpreserved in the post-shock gas. This unique Herschel data set wouldalso address outstanding questions about the disputed origin of theSpitzer green emission, interstellar H2O/NH3 abundance ratios, andthe role of outflow feedback in models of cluster formation. |
