| Description |
Water, as a dominant form of oxygen, the most abundant element
in the universe after H and He, controls the chemistry of many other
species. It is a unique diagnostic of warm gas and energetic processes
taking place during star formation.
We therefore propose to exploit the unique opportunity of Herschel to
study water in large, statistically significant, flux limited samples of massive
star forming regions detected in the recently completed ATLASGAL
submm dust continuum survey of the inner Galactic plane.
In the last years, our view of massive star forming regions has
dramatically changed by Galactic plane surveys covering cm
to IR wavelengths. These surveys enable us for the first time to
study ALL evolutionary stages of massive star formation (MSF) in an
unbiased way. Water, acting as a natural filter for warm, dense gas,
allows to probe the chemical and physical conditions in all of these
stages close to where the massive stars are forming or just have been
formed.
ATLASGAL observed submm dust continuum emission as best tracer
of the earliest phases of MSF since it is directly probing
the material from which the stars form. As a large unbiased survey
it provide the statistical base to study the scarce and short-living
protoclusters as the origin of the massive stars and the richest
clusters in the Galaxy and supplies us with a legacy value sample
of MSF regions for the water follow ups.
Water is typically seen with strongly increased
abundances in broad line wings, providing a new, sensitive probe of
shocked outflowing gas. In addition, the envelope is probed in a
combination of absorption and emission with a clear jump in
abundance in the warm inner regions close to the forming massive
stars. Only Herschel can provide a water survey of a large sample of
ATLASGAL selected sources to study water through the evolution of
massive star forming regions with a statistically significant sample size. |
