Odin water mapping in the Orion KL region

Abstract

New results from water mapping observations of the Orion KL region using the submm/mm wave satellite Odin (2.1´beam size at 557 GHz), are presented. The ortho-H2O ground state transition was observed in a rectangular grid with a spacing of 1´, while the same line of HOwas measured in two positions, Orion KL itself and 2´ south of Orion KL. In the main water species, the KL molecular outflow is largely resolved from the ambient cloud and it is found to have an extension of 60´´–110´´. The H2O outflow profile exhibits a rather striking absorption-like asymmetry at the line centre. Self-absorption in the near (or “blue”) part of the outflow (and possibly in foreground quiescent halo gas) is tentatively suggested to play a role here. We argue that the dominant part of the KL HOoutflow emission emanates from the compact (size ~15´´) low-velocity flow and here estimate an H2Oabundance of circa 10-5 compared to all H2 in the flow – an order of magnitude below earlier estimates of the H2O abundance in the shocked gas of the high-velocity flow. The narrow ambient cloud lines show weak velocity trends, both in the N-S and E-W directions. HOis detected for the first time in the southern position at a level of ~0.15 K and we here estimate an H2Oabundance of (1–8) .