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-H 2O J K(+)K(-) = l 1.0 → l 0.1 ground state transition was observed in a 7′ × 7′ rectangular grid with a spacing of 1′, while the same line of H 2 18O was 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 H 2O 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 H 2 18O outflow emission emanates from the compact (size ∼15″) low-velocity flow and here estimate an H 2O abundance of circa 10 -5 compared to all H 2 in the flow - an order of magnitude below earlier estimates of the H 2O 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. H 2 18O is detected for the first time in the southern position at a level of ∼0.15 K and we here estimate an H 2O abundance of (1-8) × 10 -8.