[P-CG27] Origin and evolution of materials in space

[PCG27-08] Detection of CH₃NCO in Galactic Center star-forming region Sagittarius B2(M) by radio astronomical observations

Yuki Ohno¹, *Mitsunori Araki¹, Yoshiaki Minami¹, Takahiro Oyama^2,1, Shuro Takano³, Nobuhiko Kuze², Yoshihiro Sumiyoshi⁴, Koichi Tsukiyama¹ (1.Tokyo University of Science, 2.Sophia University, 3.Nihon University, 4.Gunma University)

Keywords:CH3NCO, radio, molecule, Sagittarius , pre-biotic molecule

Large difference of chemical compositions between molecular clouds and comets is a big question for astrochemistry. The case of pre-biotic molecule CH₃NCO is one of them. The abundance ratio of [CH₃NCO]/[HNCO] is high in a comet (> 4, [1]), although it is low (< 0.3, [2]) in molecular clouds. An abundance of CH₃NCO is expected to be held and/or increased during evolutionary process of a cloud. A couple of an old core and a young core having the similar chemical compositions needs to be investigated for this evolutionary process. In this work, we aimed to detect CH₃NCO in the middle (M) core, which is relatively older than the north (N) core, in the Galactic Center star-forming region Sagittarius B2 with the 45 m telescope of Nobeyama Radio Observatory. The rotational transitions of J = 10→9 to 13→12 for CH₃NCO were detected in the 85–114 GHz region. The column density and the rotational temperature are derived to be N = (4.3 ± 2.1) × 10¹³ cm⁻² and T_rot = (32 ± 9) K, respectively, assuming local thermal equilibrium. Similarly, an abundance of HNCO is estimated to be N = (1.3 ± 0.5) × 10¹⁵ cm⁻² (T_rot = 21 ± 2 K), giving the ratio of [CH₃NCO]/[HNCO] = 0.032. Thus, as the simplest model, it is suggested that an abundance of CH₃NCO is held during evolutionary process of the Sagittarius B2 region.

[1] Goesmann et al., Science, 349, 689 (2015). [2] Halfen et al., ApJ, 812, L5 (2015).