Water cooling of shocks in protostellar outflows Herschel-PACS map of L1157
Journal article, 2010

Context. The far-IR/sub-mm spectral mapping facility provided by the Herschel-PACS and HIFI instruments has made it possible to obtain, for the first time, images of H2O emission with a spatial resolution comparable to ground based mm/sub-mm observations. Aims. In the framework of the Water In Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 mu m transition obtained toward the young outflow L1157. Methods. The 179 mu m map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the H2O abundance and total cooling. Results. Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 mu m emission is spatially correlated with emission from H-2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 mu m intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10(-4). This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total H2O cooling is similar to 10(-1) L-circle dot, about 40% of the cooling due to H-2 and 23% of the total energy released in shocks along the L1157 outflow.

swas

gas

stars: formation

emission

class-0 sources

ISM: molecules

ISM: jets and outflows

Author

B. Nisini

Osservatorio Astronomico di Roma

M. Benedettini

Istituto di Fisica dello Spazio Interplanetario, Rome

C. Codella

Arcetri Astrophysical Observatory

T. Giannini

Osservatorio Astronomico di Roma

René Liseau

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

D. A. Neufeld

Johns Hopkins University

M. Tafalla

Observatorio Astronomico Nacional

E. F. van Dishoeck

Max Planck Institute

Leiden University

R. Bachiller

Observatorio Astronomico Nacional

A. Baudry

Laboratoire d'Astrophysique de Bordeaux

A. O. Benz

Swiss Federal Institute of Technology in Zürich (ETH)

E. A. Bergin

University of Michigan

Per Bjerkeli

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

G. A. Blake

Caltech Division of Geological and Planetary Sciences

S. Bontemps

Laboratoire d'Astrophysique de Bordeaux

J. Braine

Laboratoire d'Astrophysique de Bordeaux

S. Bruderer

Swiss Federal Institute of Technology in Zürich (ETH)

P. Caselli

University of Leeds

Arcetri Astrophysical Observatory

J. Cernicharo

Centro de Astrobiologia (CAB)

F. Daniel

Centro de Astrobiologia (CAB)

P. Encrenaz

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

A. M. di Giorgio

Istituto di Fisica dello Spazio Interplanetario, Rome

C. Dominik

Anton Pannekoek Institute for Astronomy

Radboud University

S. Doty

Denison University

M. Fich

University of Waterloo

A. Fuente

Observatorio Astronomico Nacional

J. R. Goicoechea

Centro de Astrobiologia (CAB)

T. de Graauw

Netherlands Institute for Space Research (SRON)

F. Helmich

Netherlands Institute for Space Research (SRON)

G. J. Herczeg

Max Planck Institute

F. Herpin

Laboratoire d'Astrophysique de Bordeaux

M. Hogerheijde

Leiden University

T. Jacq

Laboratoire d'Astrophysique de Bordeaux

D. Johnstone

National Research Council Canada

University of Victoria

J. K. Jorgensen

Köbenhavns Universitet

M. Kaufman

San Jose State University

L. Kristensen

Leiden University

B. Larsson

Stockholm University

D. Lis

Caltech Division of Geological and Planetary Sciences

M. Marseille

Netherlands Institute for Space Research (SRON)

C. McCoey

University of Waterloo

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

Michael Olberg

Chalmers, Earth and Space Sciences, Onsala Space Observatory

B. Parise

Stockholm University

J. C. Pearson

Jet Propulsion Laboratory, California Institute of Technology

R. Plume

University of Calgary

C. Risacher

Netherlands Institute for Space Research (SRON)

J. Santiago

Observatorio Astronomico Nacional

P. Saraceno

Istituto di Fisica dello Spazio Interplanetario, Rome

R. Shipman

Netherlands Institute for Space Research (SRON)

T. A. van Kempen

Harvard-Smithsonian Center for Astrophysics

R. Visser

Leiden University

S. Viti

University College London (UCL)

Istituto di Fisica dello Spazio Interplanetario, Rome

S. F. Wampfler

Swiss Federal Institute of Technology in Zürich (ETH)

F. Wyrowski

Max Planck Institute

F. F. S. van der Tak

Netherlands Institute for Space Research (SRON)

University of Groningen

U. A. Yildiz

Leiden University

B. Delforge

Ecole Normale Superieure (ENS)

Radboud University

J. Desbat

Laboratoire d'Astrophysique de Bordeaux

W. A. Hatch

University of Calgary

I. Peron

Ecole Normale Superieure (ENS)

Institut de RadioAstronomie Millimetrique (IRAM)

Radboud University

R. Schieder

University of Cologne

J. A. Stern

University of Calgary

D. Teyssier

European Space Astronomy Centre (ESA)

N. Whyborn

Astronomy and Astrophysics

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

Vol. 518 Article Number: L120 L120

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201014603