| Description |
Massive star formation remains a poorly understood phenomenon, largely due to the difficulty of identifying and studying massive young stellar objects (MYSOs) in the crucial early active accretion and outflow phase. Large-scale Spitzer surveys of the Galactic Plane have yielded a promising new sample of young MYSOs with outflows, which are likely actively accreting: based on their extended 4.5 um emission in Spitzer images, these sources are known as Extended Green Objects (EGOs) from the common coding of three-color IRAC images. Extensive ground-based follow up observations revealed that the EGOs are indeed related to massive outflows from young systems with very high accretion rates (10^-3 Msun-year). They also revealed a wide variety of properties: some MYSOs appear in clusters, others are isolated, some are molecular line rich, others not. To test the hypothesis that these differences reflect evolutionary effects, we propose SPIRE-FTS and HIFI observations of 4 EGOs. SPIRE-FTS spectra of the 12CO and 13CO rotational ladders and HIFI spectra of selected CO line profiles would yield shock-excited gas temperatures and masses, constraining the current outflow (and thus accretion) activity in a more direct way than is possible in low excitation tracers with ground-based telescopes. HIFI observations of H2O and NH3 line profiles and abundances would provide independent present day outflow activity indicators and records of the shock history, as these species are formed above temperatures of 230 and 4000 K, respectively, and preserved in the post-shock gas. This unique Herschel data set would also address outstanding questions about the disputed origin of the Spitzer green emission, interstellar H2O-NH3 abundance ratios, and the role of outflow feedback in models of cluster formation. |
