First detection of ethylene oxide and acetaldehyde in hot core G358.93$-$0.03 MM1: Tracing prebiotic oxygen chemistry

Ethylene oxide (c-C${}_2$H${}_4$O) and its isomer, acetaldehyde (CH${}_3$CHO), are important complex organic molecules owing to their potential role in the formation of amino acids (R-CH(NH${}_2$)-COOH) in ISM. The detection of c-C${}_2$H${}_4$O in hot molecular cores suggests that the possible existence of larger ring-shaped molecules containing more than three carbon atoms, such as furan (c-C${}_4$H${}_4$O), which shares structural similarities with ribose (C${}_5$H${}_{10}$O5), the sugar component of DNA. In this study, we report the first detection of the rotational emission lines of c-C${}_2$H${}_4$O and CH${}_3$CHO towards the hot molecular core G358.93$-$0.03 MM1, based on observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) in band 7. The fractional abundances of c-C${}_2$H${}_4$O and CH${}_3$CHO relative to H${}_2$ are $(2.1\pm 0.2)\times {10}^{-9}$ and $(7.1\pm 0.9)\times {10}^{-9}$, respectively. The column density ratio between CH${}_3$CHO and c-C${}_2$H${}_4$O is $3.4\pm 0.7$. A Pearson correlation heat map reveals strong positive correlations ($r$ $>$ 0.5) between the abundances and excitation temperatures of c-C${}_2$H${}_4$O and CH${}_3$CHO, suggesting a possible chemical connection between those two molecules. To investigate this further, we conducted a two-phase warm-up chemical model using the gas-grain chemical code UCLCHEM. A comparison between our derived abundances and the predictions from our chemical model and existence model demonstrates good agreement within factors of 0.73 and 0.74, respectively. We propose that c-C${}_2$H${}_4$O may form in G358.93$-$0.03 MM1 via the grain surface reaction between C${}_2$H${}_4$ and O, but CH${}_3$CHO may be produced through the surface reaction between CH${}_3$ and HCO.