The GUAPOS project

Abstract

Context. Peptide-like bond molecules, which can take part in the formation of proteins in a primitive Earth environment, have been detected only towards a few hot cores and hot corinos up to now. Aims. We present a study of HNCO, HC(O)NH2, CH3NCO, CH3C(O)NH2, CH3NHCHO, CH3CH2NCO, NH2C(O)NH2, NH2C(O)CN, and HOCH2C(O)NH2 towards the hot core G31.41+0.31. The aim of this work is to study these species together to allow a consistent study among them. Methods. We have used the spectrum obtained from the ALMA 3 mm spectral survey GUAPOS, with a spectral resolution of ~0.488 MHz (~1.3–1.7 km s−1) and an angular resolution of 1.′′2 × 1.′′2 (~4500 au), to derive column densities of all the molecular species presented in this work, together with 0.′′2 × 0.′′2 (~750 au) ALMA observations from another project to study the morphology of HNCO, HC(O)NH2, and CH3C(O)NH2. Results. We have detected HNCO, HC(O)NH2, CH3NCO, CH3C(O)NH2, and CH3NHCHO, but no CH3CH2NCO, NH2C(O)NH2, NH2C(O)CN, or HOCH2C(O)NH2. This is the first time that these molecules have been detected all together outside the Galactic centre. We have obtained molecular fractional abundances with respect to H2 from 10−7 down to a few 10−9 and abundances with respect to CH3OH from 10−3 to ~4 × 10−2, and their emission is found to be compact (~2′′, i.e. ~7500 au). From the comparison with other sources, we find that regions in an earlier stage of evolution, such as pre-stellar cores, show abundances at least two orders of magnitude lower than those in hot cores, hot corinos, or shocked regions. Moreover, molecular abundance ratios towards different sources are found to be consistent between them within ~1 order of magnitude, regardless of the physical properties (e.g. different masses and luminosities), or the source position throughout the Galaxy. Correlations have also been found between HNCO and HC(O)NH2 as well as CH3NCO and HNCO abundances, and for the first time between CH3NCO and HC(O)NH2, CH3C(O)NH2 and HNCO, and CH3C(O)NH2 and HC(O)NH2 abundances. These results suggest that all these species are formed on grain surfaces in early evolutionary stages of molecular clouds, and that they are subsequently released back to the gas phase through thermal desorption or shock-triggered desorption.