A Molecular Inventory of the Orion Hot Core in Mid-Infrared with SOFIA/EXES

We present the results from a spectral line survey towards the Orion hot core IRc2 between 7.2 to 25 μm, using the EXES instrument on board the Stratospheric Observatory for IR Astronomy (SOFIA). We have established over 350 features and have identified a number of species: HNC, HCN, SO₂, CS, CH₄, SiO, H₂O, and C₂H₂. Analysis is ongoing as we build chemical models and identify more species. Our high resolution (R ~ 60,000) survey with SOFIA/EXES provides unprecedented data on the gas chemistry around the hot core in mid-infrared (MIR). Most previous high spectral resolution line surveys have been limited to radio, sub-mm, and the far-infrared wavelengths. The MIR, however, is critical for mapping rovibrational spectra and detecting molecules with no permanent dipole moment. Previous MIR missions, such as ISO and Spitzer, lacked the resolution to identify the individual rovibrational transitions of specific molecules with certainty. SOFIA/EXES is currently the only available spectrograph that provides sufficient spectral resolution in MIR for conclusive molecular identification. Though the James Webb Space Telescope (JWST) will be more sensitive than SOFIA, its low spectral resolution could lead to confusion in identifying the contribution of gaseous molecular species. The Atacama Large Millimeter/submillimeter Array (ALMA) is leading the astrochemistry field because of its exceptional sensitivity and high spectral resolution at (sub-)mm wavelengths. However, it does not have access to symmetric molecules, especially key hydrocarbons whose transitions lie in the MIR. Our SOFIA line survey will greatly enhance the inventory of bright, resolved line features in the MIR of hot cores, providing an invaluable reference for the JWST and ALMA scientific communities.