Herschel-HIFI observations of H2O, NH3 and N2H+ toward high-mass
  starless and proto-stellar clumps identified by the Hi-GAL survey
  Our present understanding of high-mass star formation still remains very
schematic. In particular, it is not yet clear how much of the difference
between low-mass and high-mass star formation occurs during the earliest star
formation phases. The chemical characteristics of massive cold clumps, and the
comparison with those of their low-mass counterparts, could provide crucial
clues about the exact role that chemistry plays in differentiating the early
phases of low-mass and high-mass star formation. Water, in particular, is a
unique probe of physical and chemical conditions in star-forming regions. Using
the HIFI instrument of Herschel we have observed the ortho-NH3 (1_0-0_0)
(572GHz), ortho-H2O (1_10-1_01) (557GHz) and N2H+ (6-5) (559GHz) lines toward a
sample of high-mass starless and proto-stellar clumps selected from the
"Herschel} Infrared Galactic Plane Survey" (Hi-GAL). We compare our results to
previous studies of low-mass and high-mass proto-stellar objects. At least one
of the three molecular lines was detected in 4 (out of 35) and 7 (out of 17)
objects in the l=59deg and l=30deg galactic regions, respectively. All detected
sources are proto-stellar. The water spectra are complex and consist of several
kinematic components, identified through a Gaussian decomposition, and in a few
sources inverse and regular P-Cygni profiles have been detected. All water line
profiles of the l=59deg region are dominated by a broad Gaussian emission
feature, indicating that the bulk of the water emission arises in outflows. No
such broad emission is detected toward the l=30deg objects. The ammonia line in
some cases also shows line wings and an inverse P-Cygni profile, thus
confirming that NH3 rotational transitions can be used to probe the dynamics of
high-mass star forming regions. Both bolometric and water line luminosity
increase with the continuum temperature.
