2015ApJ...799..102G

We present ∼2'x2' 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 H₂ 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 ¹²CO (up to J = 48-47), H₂O, OH, ¹³CO, and HCN. Peaks 1/2 are characterized by a very high L(CO)/L_FIR~ 5x10^–3 ratio and a plethora of far-IR H₂O emission lines. The high-J CO and OH lines are a factor of ~2 brighter toward Peak 1 whereas several excited H₂O 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 H₂O/CO ≲ 10^–2 abundance ratio. In addition, the very excited CO (J > 35) and H₂ O lines reveal a hotter gas component (T_k∼ 2500 K) from faster (v_S> 25 km/s) shocks that are able to sputter the frozen-out H₂O and lead to high H₂O/CO ≳ 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.