Herschelfar-Infrared Spectral-Mapping of Orion Bn/Kl Outflows: Spatial Distribution of Excited Co, H2o, Oh, O, and C+in Shocked Gas

We present ∼2' × 2' spectral-maps of Orion Becklin–Neugebauer/Kleinmann–Low (BN/KL) outflows taken with Herschel at ∼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 ∼54–310 μm spectra taken with the PACS and SPIRE spectrometers. More than 100 lines are detected, most of them rotationally excited lines of 12 CO (up to J = 48–47), H 2 O, OH, 13 CO, and HCN. Peaks 1/2 are characterized by a very high L (CO)/ L FIR ≈ 5 × 10 −3 ratio and a plethora of far-IR H 2 O emission lines. The high- J CO and OH lines are a factor of ≈2 brighter toward Peak 1 whereas several excited H 2 O lines are ≲50% brighter toward Peak 2. Most of the CO column density arises from T k ∼ 200–500 K gas that we associate with low-velocity shocks that fail to sputter grain ice mantles and show a maximum gas-phase H 2 O/CO ≲ 10 −2 abundance ratio. In addition, the very excited CO ( J > 35) and H 2 O lines reveal a hotter gas component ( T k ∼ 2500 K) from faster ( v S > 25 km s −1 ) shocks that are able to sputter the frozen-out H 2 O and lead to high H 2 O/CO ≳ 1 abundance ratios. The H 2 O 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.