H2O line mapping at high spatial and spectral resolution Herschel observations of the VLA 1623 outflow
Journal article, 2012

Context. Apart from being an important coolant, water is known to be a tracer of high-velocity molecular gas. Recent models predict relatively high abundances behind interstellar shockwaves. The dynamical and physical conditions of the water emitting gas, however, are not fully understood yet. Using the Herschel Space Observatory, it is now possible to observe water emission from supersonic molecular outflows at high spectral and spatial resolution. Several molecular outflows from young stars are currently being observed as part of the WISH (Water In Star-forming regions with Herschel) key program. Aims. We aim to determine the abundance and distribution of water, its kinematics, and the physical conditions of the gas responsible for the water emission. The observed line profile shapes help us understand the dynamics in molecular outflows. Methods. We mapped the VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFI and PACS instruments. We also present observations of higher energy transitions of o-H2O and p-H2O obtained with HIFI and PACS towards selected outflow positions. From comparison with non-LTE radiative transfer calculations, we estimate the physical parameters of the water emitting regions. Results. The observed water emission line profiles vary over the mapped area. Spectral features and components, tracing gas in different excitation conditions, allow us to constrain the density and temperature of the gas. The water emission originates in a region where temperatures are comparable to that of the warm H-2 gas (T greater than or similar to 200 K). Thus, the water emission traces a gas component significantly warmer than the gas responsible for the low-J CO emission. The water column densities at the CO peak positions are low, i.e. N(H2O) similar or equal to (0.03-10) x 10(14) cm(-2). Conclusions. The water abundance with respect to H-2 in the extended outflow is estimated at X(H2O) < 1 x 10(-6), significantly lower than what would be expected from most recent shock models. The H2O emission traces a gas component moving at relatively high velocity compared to the low-J CO emitting gas. However, other dynamical quantities such as the momentum rate, energy, and mechanical luminosity are estimated to be the same, independent of the molecular tracer used, CO or H2O.

co

protostar

rho-ophiuchi cloud

h-2

cores

stars:

molecular outflows

ISM: abundances

wave-astronomy-satellite

emission

ISM: individual objects: VLA1623

water

shock-waves

excitation

ISM: molecules

ISM: jets and outflows

Author

Per Bjerkeli

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

René Liseau

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

B. Larsson

Stockholm University

Gustaf Rydbeck

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

B. Nisini

Osservatorio Astronomico di Roma

M. Tafalla

Observatorio Astronomico Nacional

S. Antoniucci

Osservatorio Astronomico di Roma

M. Benedettini

Istituto Nazionale Di Astrofisica, Rome

Per Bergman

Chalmers, Earth and Space Sciences, Onsala Space Observatory

S. Cabrit

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

T. Giannini

Osservatorio Astronomico di Roma

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

D. A. Neufeld

Johns Hopkins University

G. Santangelo

Osservatorio Astronomico di Roma

E. F. van Dishoeck

Max Planck Institute

Leiden University

Astronomy and Astrophysics

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

Vol. 546 Article Number: A29 - A29

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201219776