FULL SYNTHESIS OBSERVATIONS OF CH_3CH_2CN IN SAGITTARIUS B2: FURTHER EVIDENCE FOR GRAIN CHEMISTRY

摘要

The first full synthesis mapping of ethyl cyanide, CH_3CH_2CN, was carried out toward Sgr B2(N-LMH), using the BIMA Array and NRAO 12 m telescope. The CH_3CH_2CN emission is confined to a region of 0.15 X 0.28 pc in the 2' x 2' mapping field. The coincidence of locations and the similarity in velocity structure between the CH_3CH_2CN emission, the optically thin ionized gas, and emission from high-density and high-excitation tracers suggest that CH_3CH_2CN is located in the hot, dense core of the star-forming region in Sgr B2(N-LMH). The emission coincides with 3 mm continuum emission that is dominated by thermal dust emission. The fractional abundance of CH_3CH_2CN is 10~(-8) in the Sgr B2(N-LMH) core, at least ～ 50 times higher than that in Sgr B2(M). The abundance differences support the scenario that abundances of complex/saturated species are greatly enhanced owing to mantle evaporation in young hot molecular cores.