Herschel Far-Infrared Spectral-mapping of Orion BN/KL Outflows: Spatial
  distribution of excited CO, H2O, OH, O and C+ in shocked gas
  We present ~2'x2' spectral-maps of Orion 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 ~54-310um
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 ~2 brighter toward Peak 1 whereas several
excited H2O lines are ~50% brighter toward Peak 2. A simplified non-LTE model
allowed us to constrain the dominant gas temperature components. Most of the CO
column density arises from Tk~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 H2O
lines reveal a hotter gas component (Tk~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.
