The Mid-infrared Molecular Inventory toward Orion IRc2

Nickerson, Sarah; Rangwala, Naseem; Colgan, Sean W. J.; DeWitt, Curtis; Monzon, Jose S.; Huang, Xinchuan; Acharyya, Kinsuk; Drozdovskaya, Maria N.; Fortenberry, Ryan C.; Herbst, Eric; Lee, Timothy J. (2023). The Mid-infrared Molecular Inventory toward Orion IRc2. Astrophysical journal, 945(1), p. 26. Institute of Physics Publishing IOP 10.3847/1538-4357/aca6e8

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We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2–28.3 μm. With SOFIA/EXES, we target the enigmatic source Orion IRc2. While this is in the most prolifically studied massive star-forming region, longer wavelengths and molecular emission lines dominated previous spectral surveys. The mid-infrared observations in this work access different components and molecular species in unprecedented detail. We unambiguously identify two new kinematic components, both chemically rich with multiple molecular absorption lines. The "blue clump" has vLSR = −7.1 ± 0.7 km s−1, and the "red clump" has 1.4 ± 0.5 km s−1. While the blue and red clumps have similar temperatures and line widths, molecular species in the blue clump have higher column densities. They are both likely linked to pure rotational H2 emission also covered by this survey. This work provides evidence for the scenario that the blue and red clumps are distinct components unrelated to the classic components in the Orion BN/KL region. Comparison to spectroscopic surveys toward other infrared targets in the region show that the blue clump is clearly extended. We analyze, compare, and present in-depth findings on the physical conditions of C2H2, 13CCH2, CH4, CS, H2O, HCN, ${{\rm{H}}}^{13}\mathrm{CN}$, HNC, NH3, and SO2 absorption lines and an H2 emission line associated with the blue and red clumps. We also provide limited analysis of H2O and SiO molecular emission lines toward Orion IRc2 and the atomic forbidden transitions [Fe ii], [S i], [S iii], and [Ne ii].

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