Water distribution in shocked regions of the NGC1333-IRAS4A protostellar outflow

Abstract

We present the study of the H2O spatial distribution at two bright shocked regions along IRAS4A, one of the strongest H2O emitters among the Class 0 outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI observations of two shocked positions. The largest HIFI beam of 38 arcsec at 557 GHz was mapped in several key water lines with different upper energy levels, to reveal possible spatial variations of the line profiles. We detect four H2O lines and CO (16-15) at the two selected positions. In addition, transitions from related outflow and envelope tracers are detected. Different gas components associated with the shock are identified in the H2O emission. In particular, at the head of the red lobe of the outflow, two distinct gas components with different excitation conditions are distinguished in the HIFI emission maps: a compact component, detected in the ground-state water lines, and a more extended one. Assuming that these two components correspond to two different temperature components observed in previous H2O and CO studies, the excitation analysis of the H2O emission suggests that the compact (about 3 arcsec) component is associated with a hot (T~1000 K) gas with densities ~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm (T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO (16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us, for the first time, to resolve spatially the two temperature components previously observed with HIFI and PACS. We propose that the compact hot component may be associated with the jet that impacts the surrounding material, whereas the warm, dense, and extended component originates from the compression of the ambient gas by the propagating flow.

13 pages, 11 figures. Accepted for publication in Astronomy and Astrophysics

References in corpus (3)

• A Flattened Protostellar Envelope in Absorption around L1157
• H2O line mapping at high spatial and spectral resolution - Herschel observations of the VLA1623 outflow
• Numerical Simulations of a Protostellar Outflow Colliding with a Dense Molecular Cloud

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• Water in star-forming regions with Herschel (WISH) V. The physical conditions in low-mass protostellar outflows revealed by multi-transition water observations
• Diagnosing shock temperature with NH${}_3$ and H${}_2$O profiles
• The warm CO gas along the UV-heated outflow cavity walls: a possible interpretation for the Herschel/PACS CO spectra of embedded YSOs
• Resolving the shocked gas in HH54 with Herschel: CO line mapping at high spatial and spectral resolution