Herschel-HIFI observations of H2O, NH3, and N2H+ toward high-mass starless and protostellar clumps identified by the Hi-GAL survey
Journal article, 2015

Context. 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. Aims. 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. Methods. Using the HIFI instrument of Herschel, we have observed the ortho−NH3 (10 −00 ) (572 GHz), ortho−H2 O (110 −101 ) (557 GHz), and N2 H+ (6−5) (559 GHz) lines toward a sample of high-mass starless and protostellar clumps selected from the Herschel Infrared Galactic Plane Survey (Hi-GAL). We compare our results to previous studies of low-mass and high-mass protostellar objects. Results. At least one of the three molecular lines was detected in 4 (out of 35) and 7 (out of 17) objects in the l = 59° and l = 30° galactic regions, respectively. All detected sources are protostellar. The water spectra are complex and consist of several kinematic components, identified through a Gaussian decomposition, and we detected inverse and regular P-Cygni profiles in a few sources. All water line profiles of the l = 59° 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 = 30° 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. Conclusions. The higher water abundance toward the l = 59° sources, characterized by the presence of outflows and shocks, supports a scenario in which the abundance of this molecule is linked to the shocked gas. Various indicators suggest that the detected sources toward the l = 30° region are in a somewhat later evolutionary phase compared to the l = 59° field, although a firm conclusion is limited by the small number of observed sources. We find many similarities with studies carried out toward low-mass protostellar objects, but there are indications that the level of infall and turbulence in the high-mass protostars studied here could be significantly higher.

star formation


L. Olmi

University of Puerto Rico

Arcetri Astrophysical Observatory

Carina Persson

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

C. Codella

Arcetri Astrophysical Observatory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 583 A125- A125

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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