Robustness of Pixel-by-Pixel Column Density and Rotational Temperature Mapping in the Orion KL Nebula

High Resolution Image Download MS PowerPoint Slide Large radio telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) are used to investigate the intimate connection between chemistry and astrophysical environment. Recently, pixel-by-pixel spectral line fitting of interferometric data has produced high spatial resolution maps of physical parameters such as column density and rotational temperature across star-forming regions. We tested the reproducibility of such methods by comparing sub-arcsecond maps of 13 CH 3 OH and CH 3 OD parameters in the Orion Kleinmann–Low (Orion KL) nebula derived from ALMA Cycle 5 and Cycle 9 observations using different rotational transitions. Maps of 13 CH 3 OH column density and rotational temperature are consistent across both observing cycles, with peak column densities of 1.2 × 10 17 cm –2 . The CH 3 OD maps differ slightly, with the column density derived from the ALMA Cycle 9 data peaking at 1.0 × 10 17 cm –2, as much as a factor of 5 less than that derived from the Cycle 5 data. This discrepancy was concluded to be predominantly the result of improved baseline subtraction. Other improvements include independently derived rotational temperatures (whereas previous work assumed a common rotational temperature for CH 3 OD and 13 CH 3 OH) and using only A-type transitions rather than a mix of A- and E-type rotational transitions for CH 3 OD. Even so, the trends between 13 CH 3 OH and CH 3 OD column densities are consistent between the two data sets; CH 3 OD abundances are enhanced at the heart of the Hot Core-SW, as demonstrated by variations in the CH 3 OD/ 13 CH 3 OH ratio across the region. These results support the robustness of pixel-by-pixel fitting of interferometric data for investigating the relationship between chemical distribution and astrophysical environment in star-forming regions.