Herschel far-infrared spectral-mapping of orion bn/kl outflows: spatialdistribution of excited co, h2o, oh, o, and c+ in shocked gas

Abstract

We present similar to 2; x 2' spectral-maps of Orion Becklin-Neugebauer/Kleinmann-Low (BN/KL) outflows taken with Herschel at similar to 12 '' resolution. For the first time in the far-IR domain, we spatially resolve the emission associated with the bright H-2 shocked regions "Peak 1" and "Peak 2" from that of the hot core and ambient cloud. We analyze the similar to 54-310 mu m spectra taken with the PACS and SPIRE spectrometers. More than 100 lines are detected, most of them rotationally excited lines of (CO)-C-12 (up to J = 48-47), H2O, OH, (CO)-C-13, and HCN. Peaks 1/2 are characterized by a very high L(CO)/L-FIR approximate to 5 x 10(-3) ratio and a plethora of far-IR H2O emission lines. The high-J CO and OH lines are a factor of approximate to 2 brighter toward Peak 1 whereas several excited H2O lines are less than or similar to 50% brighter toward Peak 2. Most of the CO column density arises from T-k similar to 200-500 K gas that we associate with low-velocity shocks that fail to sputter grain ice mantles and show a maximum gas-phase H2O/CO less than or similar to 10(-2) abundance ratio. In addition, the very excited CO (J > 35) and H2O lines reveal a hotter gas component (T-k similar to 2500 K) from faster (v(S) > 25 km s(-1)) shocks that are able to sputter the frozen-out H2O and lead to high H2O/CO greater than or similar to 1 abundance ratios. The H2O and OH luminosities cannot be reproduced by shock models that assume high (undepleted) abundances of atomic oxygen in the preshock gas and/or neglect the presence of UV radiation in the postshock gas. Although massive outflows are a common feature in other massive star-forming cores, Orion BN/KL seems more peculiar because of its higher molecular luminosities and strong outflows caused by a recent explosive event.