Spatial distribution of HOCN around Sagittarius B2

TL;DR

This study maps the distribution of HOCN and HNCO around Sagittarius B2, revealing their abundance ratios and providing insights into their formation mechanisms and isotopic ratios in this region.

Contribution

First high-sensitivity mapping of HOCN and HNCO around Sagittarius B2, analyzing abundance ratios and isotopic ratios to understand chemical processes.

Findings

HOCN/HNCO abundance ratio ranges from 0.4% to 0.7% in most regions

Enhanced HOCN abundance (~0.9%) observed toward Sagittarius B2 (S)

Updated $^{16}$O/$^{18}$O isotopic ratio to 296 ± 54 in Sgr 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.