ALMA Observations of the Spatial Distribution of three $\mathrm{C_2H_4O_2}$ Isomers towards Sgr B2(N)

Ci Xue, Anthony J. Remijan, Andrew M. Burkhardt, Eric Herbst

Published 2018-12-17Version 1

The $\mathrm{C_2H_4O_2}$ 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 (Belloche et al. 2013). In this study, we present an intensive and rigorous spectral and morphological analysis of the $\mathrm{C_2H_4O_2}$ isomers towards Sgr B2(N) with interferometers, ALMA 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 maps of the $\mathrm{C_2H_4O_2}$ isomers reveal that $\mathrm{HCOOCH_3}$ and $\mathrm{CH_2OHCHO}$ each display two different velocity components, while only one velocity component of $\mathrm{CH_3COOH}$ is resolved. Moreover, the distribution of $\mathrm{HCOOCH_3}$ is extended and offset from the continuum emission, unlike $\mathrm{CH_2OHCHO}$ and $\mathrm{CH_3COOH}$, 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 $\mathrm{C_2H_4O_2}$ isomeric species indicate that $\mathrm{HCOOCH_3}$ have significant differences in chemical processes than $\mathrm{CH_2OHCHO}$ and $\mathrm{CH_3COOH}$, which display similar spatial distributions.