[P-CG19] Origin and evolution of materials in space

[PCG19-P01] Investigation of Dust-Surface Formation of Prebiotic Molecule CH₃NCO in Star-Forming Region Sagittarius B2(N)

*Mitsunori Araki¹, Kyoichi Izuoka¹, Yuki Ohno¹, Takahiro Oyama², Shuro Takano³, Nobuhiko Kuze², Koichi Tsukiyama¹ (1.Tokyo University of Science, 2.Sophia University, 3.Nihon University)

Keywords:ALMA, Prebiotic Molecule, Methyl isocyanate

Origin of organic molecules on Earth is thought to be interstellar clouds because comets carried molecules produced in clouds. Methyl isocyanate CH₃NCO is presumably one of delivered organic molecules at the primitive earth. However, observed abundance ratios of [CH₃NCO]/[HNCO] in molecular clouds [1] are clearly lower than that in the comet 67P [2]. Recently a theoretical study has suggested that this abundance anomaly can be explained by dust-surface formation of CH₃NCO in molecular clouds [3]. If that is the case, high-temperature CH₃NCO desorbed from dust surface makes a dense distribution in a central region of a star-forming core. To examine this condition, the spatial and spectral data of CH₃NCO toward the core of the high-mass star-forming region Sagittarius B2(N) in 94–113 GHz observed by the ALMA radio telescope were analyzed. Considering intensity maps and velocity structures, it was found that CH₃NCO shows a structure of a bipolar molecular flow and an accretion disk. Rotational temperatures are derived to be 20–50 and 50–60 K in the flow and the disk, respectively, and column densities of both the sources are ~10¹⁵ cm⁻². These results suggest hot and dense conditions of this molecule in the central region of the core. Hence, CH₃NCO detected in the present data is likely to be produced on dust surface.
[1] Halfen et al., 2015, ApJL, 812, L5. [2] Goesmann et al., 2015, Sci., 349, 6247. [3] Majumdar et al., 2018, MNRAS, 473, L59.