2019ApJ...871..112X

The C₂H₄O₂ isomers have been previously investigated primarily via disparate sets of observations involving single-dish and array measurements. The only attempt at using a uniform set of observations was performed with the IRAM 30 m observation in 2013. In this study, we present an intensive and rigorous spectral and morphological analysis of the C₂H₄O₂ isomers toward Sgr B2(N) with interferometers, Atacama Large Millimeter/submillimeter Array Band 3 observations. We propose a quantitative selection method, which automates the determination of the most uncontaminated transitions and allows us to report the discovery of previously undetected transitions of the three isomers. With the least contaminated transitions, the high spatial-resolution millimeter (mm) maps of the C₂H₄O₂ isomers reveal that HCOOCH₃ and CH₂OHCHO each display two different velocity components, while only one velocity component of CH₃COOH is resolved. Moreover, the distribution of HCOOCH₃ is extended and offset from the continuum emission, unlike CH₂OHCHO and CH₃COOH, for which the low-velocity component is found to be compact and concentrated toward the continuum emission peak of Sgr B2(N). The distinct morphologies of these C₂H₄O₂ isomeric species indicate that HCOOCH₃ have significant differences in chemical processes compared to CH₂OHCHO and CH₃COOH, which display similar spatial distributions.