Mapping Physical Parameters in Orion KL at High Spatial Resolution

The Orion Kleinmann-Low nebula (Orion KL) is notoriously complex and exhibits a range of physical and chemical components. We conducted high-angular-resolution (subarcsecond) observations of (CH3OH)-C-13 nu = 0 (similar to 0.'' 3 and similar to 0.'' 7) and CH3CN nu (8) = 1 (similar to 0.'' 2 and similar to 0.'' 9) line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate Orion KL's structure on small spatial scales (<= 350 au). Gas kinematics, excitation temperatures, and column densities were derived from the molecular emission via a pixel-by-pixel spectral line fitting of the image cubes, enabling us to examine the small-scale variation of these parameters. Subregions of the Hot Core have a higher excitation temperature in a 0.'' 2 beam than in a 0.'' 9 beam, indicative of possible internal sources of heating. Furthermore, the velocity field includes a bipolar similar to 7-8 km s(-1) feature with a southeast-northwest orientation against the surrounding similar to 4-5 km s(-1) velocity field, which may be due to an outflow. We also find evidence of a possible source of internal heating toward the Northwest Clump, since the excitation temperature there is higher in a smaller beam versus a larger beam. Finally, the region southwest of the Hot Core (Hot Core-SW) presents itself as a particularly heterogeneous region bridging the Hot Core and Compact Ridge. Additional studies to identify the (hidden) sources of luminosity and heating within Orion KL are necessary to better understand the nebula and its chemistry.

Automated summary

Using high-angular-resolution observations with ALMA, we investigated the structure and variation of physical and chemical components in the Orion KL nebula on small spatial scales. We found that subregions of the Hot Core have higher excitation temperatures in smaller scales, indicating possible internal heating sources. Additionally, a bipolar feature with a southeast-northwest orientation was observed in the velocity field, suggesting the presence of an outflow. Evidence of a possible internal heating source toward the Northwest Clump was also identified. The Hot Core-SW region was identified as a particularly heterogeneous region bridging the Hot Core and Compact Ridge.