2024ApJ...961...58Z

Peptide-like molecules, which have a close connection with the origin of life, have been detected in the Universe. Mapping observations of HCONH₂ and CH₃CONH₂, 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 HCONH₂ and five transitions of CH₃CONH₂ are used in the analysis. The spatial distributions of the excitation temperature and column density of HCONH₂ in the molecular envelope of Sgr B2 are obtained by rotation diagrams. Assuming the same excitation temperature of HCONH₂, the column densities of CH₃CONH₂ 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 HCONH₂ and CH₃CONH₂ are calculated to explore the relationship between them, as are those between HCONH₂ and HNCO. The abundance ratio of CH₃CONH₂/HCONH₂ varies from 10% to 20%, while that of HCONH₂/HNCO ranges from 1.5% to 10%. CH₃CONH₂ is enhanced with respect to HCONH₂ in the northwest region of Sgr B2. One transition of H¹³CONH₂ is detected toward 12 positions of Sgr B2, from which a ¹²C/¹³C 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 HCONH₂ and CH₃CONH₂, 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.