Analysis of the Herschel/HEXOS Spectral Survey Towards Orion South: A massive protostellar envelope with strong external irradiation

Abstract

We present results from a comprehensive submillimeter spectral survey toward the source Orion South, based on data obtained with the HIFI instrument aboard the \textit{Herschel Space Observatory}, covering the frequency range 480 to 1900 GHz. We detect 685 spectral lines with S/N $>$ 3$\sigma$, originating from 52 different molecular and atomic species. We model each of the detected species assuming conditions of Local Thermodynamic Equilibrium. This analysis provides an estimate of the physical conditions of Orion South (column density, temperature, source size, \& V${}_{LSR}$). We find evidence for three different cloud components: a cool (T${}_{ex}\sim 20-40$ K), spatially extended ($>60"$), and quiescent ($\Delta V_{FWHM}\sim 4$ km s ${}^{-1}$) component; a warmer (T${}_{ex}\sim 80-100$ K), less spatially extended ($\sim 30"$), and dynamic ($\Delta V_{FWHM}\sim 8$ km s ${}^{-1}$) component, which is likely affected by embedded outflows; and a kinematically distinct region (T${}_{ex}$ $>$ 100 K; V${}_{LSR}$ $\sim$ 8 km s ${}^{-1}$), dominated by emission from species which trace ultraviolet irradiation, likely at the surface of the cloud. We find little evidence for the existence of a chemically distinct "hot core" component, likely due to the small filling factor of the hot core or hot cores within the \textit{Herschel} beam. We find that the chemical composition of the gas in the cooler, quiescent component of Orion South more closely resembles that of the quiescent ridge in Orion-KL. The gas in the warmer, dynamic component, however, more closely resembles that of the Compact Ridge and Plateau regions of Orion-KL, suggesting that higher temperatures and shocks also have an influence on the overall chemistry of Orion South.

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Cited by in corpus (9)

• Structure of photodissociation fronts in star-forming regions revealed by observations of high-J CO emission lines with Herschel
• Thermal Jeans fragmentation within 1000 AU in OMC-1S
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• CO Spectral Line Energy Distributions in Galactic Sources: Empirical Interpretation of Extragalactic Observations
• The role of highly vibrationally excited H2 initiating the N chemistry: Quantum study and 3-sigma detection of NH emission in the Orion Bar PDR
• A Q-band line survey towards Orion KL using the Tianma radio telescope
• Molecular tracers of radiative feedback in Orion (OMC-1). Widespread CH+ (J=1-0), CO (10-9), HCN (6-5), and HCO+ (6-5) emission
• Hunting for the elusive methylene radical
• G331.512-0.103: An Interstellar Laboratory for Molecular Synthesis I. The Ortho-to-para Ratios for CH${}_3$OH and CH${}_3$CN