2024MNRAS.533.1143M

The identification of complex pre-biotic molecules using millimetre and submillimetre telescopes allows us to understand how the basic building blocks of life are formed in the universe. In the interstellar medium, ethylene glycol ($({\rm CH}_2{\rm OH})_{2}$) is the simplest sugar alcohol molecule, and it is the reduced alcohol of the simplest sugar-like molecule, glycolaldehyde (${\rm CH}_{2}{\rm OHCHO}$). We present the detection of the rotational emission lines of $aGg^{\prime }$ conformer of ethylene glycol ($({\rm CH}_2{\rm OH})_{2}$) towards the hot molecular core G358.93-0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array. The estimated column density of $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ towards the G358.93-0.03 MM1 is (4.5$\pm 0.1)\times 10^{16}$ cm$^{-2}$ with an excitation temperature of 155$\pm$35 K. The abundance of $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ with respect to ${\rm H}_{2}$ is (1.4$\pm 0.5)\times 10^{-8}$. Similarly, the abundances of $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ with respect to ${\rm CH}_{2}{\rm OHCHO}$ and ${\rm CH}_{3}{\rm OH}$ are 3.1$\pm$0.5 and (6.1$\pm 0.3)\times 10^{-3}$. We compare the estimated abundance of $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ with the existing three-phase warm-up chemical model abundance of $({\rm CH}_2{\rm OH})_{2}$, and we notice the observed abundance and modelled abundance are nearly similar. We discuss the possible formation pathways of $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ towards the hot molecular cores, and we find that $aGg^{\prime }$-$({\rm CH}_2{\rm OH})_{2}$ is probably created via the recombination of two ${\rm CH}_{2}{\rm OH}$ radicals on the grain surface of G358.93-0.03 MM1.