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 ($\text{NH2CH2COOH}$), 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 $\text{NH2CH2COOH}$ in the ISM at millimeter and submillimeter wavelengths have failed. Since the detection of $\text{NH2CH2COOH}$ in the ISM is extremely difficult, we aime to search for the possible precursors of $\text{NH2CH2COOH}$. Earlier, many laboratory experiments have suggested that methylamine ($\text{CH3NH2}$) plays an important role in the ISM as a possible precursor of $\text{NH2CH2COOH}$. After spectral analysis using the local thermodynamic equilibrium (LTE) model, we identified the rotational emission lines of $\text{CH3NH2}$ towards the hot molecular core G358.93–0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array (ALMA). The column density of $\text{CH3NH2}$ towards the G358.93–0.03 MM1 is estimated to be (1.10 ± 0.31)$\times$10¹⁷ cm⁻² with an excitation temperature of 180.8 ± 25.5 K. The fractional abundance of $\text{CH3NH2}$ with respect to $\text{H2}$ towards the G358.93–0.03 MM1 is (8.80 ± 2.60)$\times$10⁻⁸. The column density ratio of $\text{CH3NH2}$ and $\text{NH2CN}$ towards G358.93–0.03 MM1 is (1.86 ± 0.95)$\times$10². The estimated fractional abundance of $\text{CH3NH2}$ towards the G358.93–0.03 MM1 agrees fairly well with the previous three-phase warm-up chemical modelling abundance of $\text{CH3NH2}$. We also discuss the possible formation mechanism of $\text{CH3NH2}$, and we find that $\text{CH3NH2}$ is most probably formed via the reactions of radical $\text{CH3}$ and radical $\text{NH2}$ on the grain surface of G358.93–0.03 MM1.