The prebiotic molecular inventory of Serpens SMM1: II. The building blocks of peptide chains

Abstract

This work aims to constrain the abundances of interstellar amides, by searching for this group of prebiotic molecules in the intermediate-mass protostar Serpens SMM1-a. ALMA observations are conducted toward Serpens SMM1. A spectrum is extracted toward the SMM1-a position and analyzed with the CASSIS line analysis software for the presence of characteristic rotational lines of a number of amides and other molecules. NH 2 CHO, NH 2 CHO ν 12 =1, NH 13 2 CHO, CH 3 C(O)NH 2 ν=0,1, CH 2 DOH, CH 3 CHO, and CH 3 C(O)CH 3 are securely detected, while trans-NHDCHO, NH 2 CDO, CH 3 NHCHO ν=0,1, CH 3 COOH, and HOCH 2 CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH 3 C(O)NH 2 /NH 2 CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH 3 NHCHO, based on a smaller data sample. The D/H ratio of NH 2 CHO is about 1-3% and is close to values found in the low-mass source IRAS 16293-2422B. The formation of CH 3 C(O)NH 2 and NH 2 CHO is likely linked. Formation of these molecules on grain surfaces during the dark cloud stage is a likely scenario. The high D/H ratio of NH 2 CHO is also seen as an indicationthat these molecules are formed on icy dust grains. As a direct consequence, amides are expected to be present in the most pristine material from which planetary systems form, thus providing a reservoir of prebiotic material.