Astrophys. J., 799, 102 (2015/January-3)
Herschel far-infrared spectral-mapping of Orion BN/KL outflows: spatial distribution of excited CO, H2O, OH, O, and c+ in shocked gas.
GOICOECHEA J.R., CHAVARRIA L., CERNICHARO J., NEUFELD D.A., VAVREK R., BERGIN E.A., CUADRADO S., ENCRENAZ P., ETXALUZE M., MELNICK G.J. and POLEHAMPTON E.
Abstract (from CDS):
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)/LFIR~ 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 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 H2 O lines reveal a hotter gas component (Tk∼ 2500 K) from faster (vS> 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.
infrared: ISM - ISM: jets and outflows - shock waves - stars: protostars
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