Mapping Observations of Peptide-like Molecules around Sagittarius B2
Siqi Zheng, Juan Li, Junzhi Wang, Yao Wang, F. Gao, Donghui Quan, Fujun Du, Yajun Wu, Edwin A. Bergin, Yuqiang Li
Abstract
Abstract Peptide-like molecules, which have a close connection with the origin of life, have been detected in the Universe. Mapping observations of HCONH 2 and CH 3 CONH 2 , two of the simplest peptide-like molecules, are performed toward the Sagittarius B2 (Sgr B2) complex with the IRAM 30 m telescope. Seven transitions of HCONH 2 and five transitions of CH 3 CONH 2 are used in the analysis. The spatial distributions of the excitation temperature and column density of HCONH 2 in the molecular envelope of Sgr B2 are obtained by rotation diagrams. Assuming the same excitation temperature of HCONH 2 , the column densities of CH 3 CONH 2 are also calculated. The results show that the excitation temperature ranges from 6 to 46 K in the molecular envelope of Sgr B2. The abundance ratios between HCONH 2 and CH 3 CONH 2 are calculated to explore the relationship between them, as are those between HCONH 2 and HNCO. The abundance ratio of CH 3 CONH 2 /HCONH 2 varies from 10% to 20%, while that of HCONH 2 /HNCO ranges from 1.5% to 10%. CH 3 CONH 2 is enhanced with respect to HCONH 2 in the northwest region of Sgr B2. One transition of H 13 CONH 2 is detected toward 12 positions of Sgr B2, from which a 12 C/ 13 C ratio of 28.7 is obtained. A time-dependent chemical model with a short-duration X-ray burst is used to explain the observed abundances of HCONH 2 and CH 3 CONH 2 , with the best-fitting result at T dust = 53–56 K. More chemical reactions are required to be included in the model since the modeled abundance is lower than the observed one at the observed T dust .