The Mid-infrared Molecular Inventory toward Orion IRc2

Abstract

We present the first high spectral resolution mid-infrared survey in the Orion BN/KL region, covering 7.2–28.3 μ m. 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 v _LSR = −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 H _2 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 C _2 H _2 , ^13 CCH _2 , CH _4 , CS, H _2 O, HCN, ${{\rm{H}}}^{13}\mathrm{CN}$ , HNC, NH _3 , and SO _2 absorption lines and an H _2 emission line associated with the blue and red clumps. We also provide limited analysis of H _2 O and SiO molecular emission lines toward Orion IRc2 and the atomic forbidden transitions [Fe ii ], [S i ], [S iii ], and [Ne ii ].

Keywords

• Infrared astronomy
• Interstellar medium
• Molecular spectroscopy
• Spectral line identification
• Molecular physics
• Astrochemistry