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

Abstract

Ethylene oxide (c-

) and its isomer, acetaldehyde (CH₃CHO), are important complex organic molecules owing to their potential role in the formation of amino acids (R–CH(NH₂)-COOH) in interstellar medium. The detection of c-

in hot molecular cores suggests the possible existence of larger ring-shaped molecules containing more than three carbon atoms, such as furan (c-

), which shares structural similarities with ribose (C₅H₁₀O₅), the sugar component of DNA. In this study, we report the first detection of the rotational emission lines of c-

and CH₃CHO 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-

and CH₃CHO relative to H₂ are $(2.1\pm 0.2)\times 10^{-9}$ and $(7.1\pm 0.9)\times 10^{-9}$, respectively. The column density ratio between CH₃CHO and c-

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-

and CH₃CHO, 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-

may form in G358.93–0.03 MM1 via the grain surface reaction between C₂H₄ and O, but CH₃CHO may be produced through the surface reaction between CH₃ and HCO.