| 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. |
