Herschel observations of Extra-Ordinary Sources: H2S as a Probe of Dense Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core

Abstract

We present Herschel/HIFI observations of the light hydride H${}_2$S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the HEXOS GT key program. In total, we observe 52, 24, and 8 unblended or slightly blended features from H${}_2$${}^{32}$S, H${}_2$${}^{34}$S, and H${}_2$${}^{33}$S, respectively. We only analyze emission from the so called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H${}_2$S follow straight lines given the uncertainties and yield T${}_{\mathrm{rot}}$=141$\pm$12 K. This indicates H${}_2$S is in LTE and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E${}_{\mathrm{up}}$>1000 K) are likely populated primarily by radiation pumping. We derive an H${}_2$${}^{32}$S column density, N${}_{\mathrm{tot}}$(H${}_2$${}^{32}$S)=9.5$\pm$1.9$\times$10${}^{17}$ cm${}^{-2}$, gas kinetic temperature, T${}_{\mathrm{kin}}$=120${\pm }_{10}^{13}$ K, and constrain the H${}_2$ volume density, n${}_{H2}$>9$\times$10${}^7$ cm${}^{-3}$, for the H${}_2$S emitting gas. These results point to an H${}_2$S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KL's high luminosity. We also derive an H${}_2$S ortho/para ratio of 1.7$\pm$0.8 and set an upper limit for HDS/H2S of <4.9$\times$10${}^{-3}$.

46 pages, 13 figures, 6 tables. Accepted for publication to ApJ

References in corpus (5)

• The distance to the Orion Nebula
• Low sulfur depletion in the Horsehead PDR
• Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2
• S-bearing molecules in Massive Dense Cores
• A far-infrared molecular and atomic line survey of the Orion KL region

Cited by in corpus (28)

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