Mapping Observations of complex organic molecules around Sagittarius B2 with ARO 12m telescope

Abstract

We performed high-sensitivity mapping observations of several complex organic molecules around Sagittarius B2 with ARO 12m telescope at 3-mm wavelength. Based on their spatial distribution, molecules can be classified as either "extended" that detected not only in Sgr B2(N) and Sgr B2(M), or "compact" that only detected toward or near to Sgr B2(N) and Sgr B2(M). The "extended" molecules including glycolaldehyde (CH 2 OHCHO), methyl formate (CH 3 OCHO), formic acid (t-HCOOH), ethanol (C 2 H 5 OH) and methyl amine (CH 3 NH 2 ), while the "compact" molecules including dimethyl ether (CH 3 OCH 3 ), ethyl cyanide (C 2 H 5 CN), and amino acetonitrile (H 2 NCH 2 CN). These "compact" molecules are likely produced under strong UV radiation, while "extended" molecules are likely formed under low-temperature, via gasphase or grain surface reactions. The spatial distribution of "warm" CH 2 OHCHO at 89 GHz differ from the spatial distribution of "cold" CH 2 OHCHO observed at 13 GHz. We found evidence for an overabundance of CH 2 OHCHO compared to that expected from the gas-phase model, which indicates that grain-surface reactions are necessary to explain the origin of CH 2 OHCHO in Sagittarius B2. Grain-surface reactions are also needed to explain the correlation between the abundances of "cold" CH 2 OHCHO and C 2 H 5 OH. These results demonstrate the importance of grain-surface chemistry in the production of complex organic molecules.