ALMA Observations of the Spatial Distribution of three C$_2$H$_4$O$_2$ Isomers towards Sgr B2(N)

TL;DR

This study uses ALMA interferometric observations to analyze the spatial distribution and velocity components of three C$_2$H$_4$O$_2$ isomers in Sgr B2(N), revealing distinct morphologies and chemical process implications.

Contribution

It introduces a quantitative selection method for uncontaminated transitions and reports new detections, providing detailed spatial and velocity analysis of the isomers.

Findings

HCOOCH$_3$ and CH$_2$OHCHO each show two velocity components.

HCOOCH$_3$ distribution is extended and offset from continuum.

CH$_2$OHCHO and CH$_3$COOH have similar, compact distributions.

Abstract

The C$_2$H$_4$O$_2$ 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 C$_2$H$_4$O$_2$ 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 C$_2$H$_4$O$_2$ isomers reveal that HCOOCH$_3$ and CH$_2$OHCHO each display two different velocity components, while only one velocity component of CH$_3$COOH is resolved. Moreover, the distribution of HCOOCH$_3$ is extended and offset from the continuum emission, unlike CH$_2$OHCHO and CH$_3$COOH, 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 C$_2$H$_4$O$_2$ isomeric species indicate that HCOOCH$_3$ have significant differences in chemical processes than CH$_2$OHCHO and CH$_3$COOH, which display similar spatial distributions.