Water distribution in shocked regions of the NGC 1333-IRAS 4A protostellar outflow

Abstract

Context. Water is a key molecule in protostellar environments because its line emission is very sensitive to both the chemistry and the physical conditions of the gas. Observations of H 2 O line emission from low-mass protostars and their associated outflows performed with HIFI onboard the Herschel Space Observatory have highlighted the complexity of H 2 O line profiles, in which different kinematic components can be distinguished. Aims. The goal is to study the spatial distribution of H 2 O, in particular of the different kinematic components detected in H 2 O emission, at two bright shocked regions along IRAS 4A, one of the strongest H 2 O emitters among the Class 0 outflows. Methods. We obtained Herschel-PACS maps of the IRAS 4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38 at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. A large velocity gradient (LVG) analysis was performed to determine the excitation conditions of the gas.