The GUAPOS project

II. A comprehensive study of peptide-like bond molecules^★

¹ Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir Km. 4, 28850, Torrejón de Ardoz, Madrid, Spain
e-mail: lcolzi@cab.inta-csic.es
² INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Florence, Italy
³ Università degli studi di Firenze, Dipartimento di fisica e Astronomia, Via Sansone 1, 50019 Sesto Fiorentino, Italy
⁴ INAF-IAPS, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ Dipartimento di Chimica “Giacomo Ciamician”, Università di Bologna, Via F. Selmi 2, 40126 Bologna, Italy
⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁷ University of Leiden, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁹ Grupo de Espectroscopia Molecular (GEM), Edificio Quifima, Área de Química-Física, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Unidad Asociada CSIC, Universidad de Valladolid, 47011 Valladolid, Spain
¹⁰ Department of Analytical Chemistry, University of Chemistry and Technology, Technická 5, 166 28 Prague 6, Czech Republic

Received: 16 June 2021
Accepted: 23 July 2021

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.