Detection of possible glycine precursor molecule methylamine towards the hot molecular core G358.93$-$0.03 MM1

Abstract: The search for the simplest amino acid, glycine (NH${2}$CH${2}$COOH), in the interstellar medium (ISM), has become a never-ending story for astrochemistry and astrophysics researchers because that molecule plays a possible connection between the Universe and the origin of life. In the last forty years, all searches for NH${2}$CH${2}$COOH in the ISM at millimeter and submillimeter wavelengths have failed. Since the detection of NH${2}$CH${2}$COOH in the ISM was extremely difficult, we aimed to search for the possible precursors of NH${2}$CH${2}$COOH. Earlier, many laboratory experiments have suggested that methylamine (CH${3}$NH${2}$) plays an important role in the ISM as a possible precursor of NH${2}$CH${2}$COOH. After spectral analysis using the local thermodynamic equilibrium (LTE) model, we identified the rotational emission lines of CH${3}$NH${2}$ towards the hot molecular core G358.93$-$0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array (ALMA). The column density of CH${3}$NH${2}$ towards the G358.93$-$0.03 MM1 was estimated to be (1.10$\pm$0.31)$\times$10$^{17}$ cm$^{-2}$ with an excitation temperature of 180.8$\pm$25.5 K. The fractional abundance of CH${3}$NH${2}$ with respect to H${2}$ towards the G358.93$-$0.03 MM1 was (8.80$\pm$2.60)$\times$10$^{-8}$. The column density ratio of CH${3}$NH${2}$ and NH${2}$CN towards G358.93$-$0.03 MM1 was (1.86$\pm$0.95)$\times$10$^{2}$. The estimated fractional abundance of CH${3}$NH${2}$ towards the G358.93$-$0.03 MM1 agrees fairly well with the previous three-phase warm-up chemical modelling abundance of CH${3}$NH${2}$. We also discussed the possible formation mechanism of CH${3}$NH${2}$, and we find that CH${3}$NH${2}$ is most probably formed via the reactions of radical CH${3}$ and radical NH${2}$ on the grain surface of G358.93$-$0.03 MM1.