The Difference in Abundances between N-bearing and O-bearing Species in High-Mass Star-Forming Regions
Résumé
The different distributions of N-bearing species and O-bearing species, as is well known towards Orion~KL, is one of the long lasting mysteries in the astrochemistry. We conducted a survey observation and chemical modeling study to understand the difference in N-bearing and O-bearing species. First, we report our observational results of complex organic molecules (COMs) with the 45~m radio telescope at the Nobeyama Radio Observatory. Through our spectral survey ranging from 80 to 108~GHz, we detected CH$_3$OH, HCOOCH$_3$, CH$_3$OCH$_3$, (CH$_3$)$_2$CO, CH$_3$CHO, CH$_3$CH$_2$CN, CH$_2$CHCN, and NH$_2$CHO. Their molecular abundances were derived via the rotation diagram and the least squares methods. N-bearing molecules, CH$_3$CH$_2$CN, CH$_2$CHCN, and NH$_2$CHO tend to show stronger correlations with other N-bearing molecules rather than O-bearing molecules. This relationship suggests that the correlation of abundance of O- species and N-bearing species is ubiquitous in hot cores. Then, our observational results were evaluated by chemical modeling with NAUTILUS three-phase gas-grain chemical code. Through the simulations of time evolutions for the abundances of COMs, we suggest that observed correlations between COMs can be explained by the combination of the different temperature structures inside the hot cores and the different evolutionary phase. On the other hand, our modeling could not fully explain the observed excitation temperatures, requiring more sophistication of our chemical model. It is important to investigate the efficiency of grain surface reactions and their activation barriers, and the binding energy of COMs to further promote our understanding of hot core chemistry.