Spatial distribution of HOCN around Sagittarius B2

Abstract

HOCN and HNCO abundance ratio in molecular gas can tell us the information of their formation mechanism. We performed high-sensitivity mapping observations of HOCN, HNCO, and HNC${}^{18}$O lines around Sagittarius B2 (Sgr B2) with IRAM 30m telescope at 3-mm wavelength. HNCO 4${}_{04}$-3${}_{03}$ and HOCN 4${}_{04}$-3${}_{03}$ are used to obtain the abundance ratio of HNCO to HOCN. The ratio of HNCO 4${}_{04}$-3${}_{03}$ to HNC${}^{18}$O 4${}_{04}$-3${}_{03}$ is used to calculate the optical depth of HNCO 4${}_{04}$-3${}_{03}$. The abundance ratio of HOCN and HNCO is observed to range from 0.4% to 0.7% toward most positions, which agrees well with the gas-grain model. However, the relative abundance of HOCN is observed to be enhanced toward the direction of Sgr B2 (S), with HOCN to HNCO abundance ratio of $\sim$ 0.9%. The reason for that still needs further investigation.Based on the intensity ratio of HNCO and HNC${}^{18}$O lines, we updated the isotopic ratio of ${}^{16}$O/${}^{18}$O to be 296 $\pm$ 54 in Sgr B2.

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