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High-Resolution Imaging of Chemistry in the Orion Kleinmann-Low Nebula

Presentation #135.01D in the session Molecular Cloud Chemistry.

Published onJun 29, 2022
High-Resolution Imaging of Chemistry in the Orion Kleinmann-Low Nebula

Advancements in imaging technologies have changed the ways in which we see and understand our chemical universe. Given the extreme distances between Earth and molecular clouds, we cannot resolve the chemical structure of these interstellar laboratories on the same scales as we can with samples on Earth. Nevertheless, with the advent of larger and more sophisticated telescopes, such as the Atacama Large Millimeter/submillimeter Array (ALMA), we can now look at interstellar chemistry on solar system scales. The chemistry of the Orion Kleinmann-Low nebula (Orion KL), the closest massive star-forming region to us, has been studied extensively, but there is still much left to learn. We use the high-angular-resolution capabilities of ALMA to complement past lower-resolution observations of Orion KL’s chemistry. Using methanol and methyl cyanide as molecular probes, we provide new insight into the thermal structure of the nebula by mapping physical parameters derived from observed spectra. We also use different isotopologues of methanol to understand this compound’s chemistry. Methanol is widely accepted to form on icy dust grains, but how it is injected into the gas phase where it is observed by radio telescopes is less constrained. Our results suggest thermal desorption is the primary driver of observed gas-phase methanol in Orion KL. Another ongoing question about methanol chemistry concerns the relative abundances of its singly-deuterated isotopologues. Specifically, the relative abundance of CH3OD is higher than expected in Orion KL and other massive star-forming regions. Our observations show a temperature dependence of CH3OD abundances in certain parts of the nebula. This work provides a new view of Orion KL by providing high-angular-resolution maps of parameters such as abundance and temperature, whereas much of the existing literature provides a single set of parameters for a region. Furthermore, mapping the relationship between abundance and temperature at small spatial scales provides a framework for follow-up experimental and theoretical investigations to better understand Orion KL’s chemistry.

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