Methylamine and other simple N-bearing species in the hot cores NGC 6334I MM1–3

In the search for the building blocks of life, nitrogen-bearing molecules are of particular interest since nitrogen-containing bonds are essential for the linking of amino acids and ultimately the formation of larger biological structures. The elusive molecule methylamine (CH₃NH₂) is thought to be a key pre-biotic species but has so far only been securely detected in the giant molecular cloud Sgr B2. We identify CH₃NH₂ and other simple nitrogen-bearing species towards three hot cores in NGC 6334I. Column density ratios are derived in order to investigate the relevance of the individual species as precursors of biotic molecules. Observations obtained with ALMA were used to study transitions of CH₃NH₂, CH₂NH, NH₂CHO, and the ¹³C- and ¹⁵N-methyl cyanide (CH₃CN) isotopologues. Column densities are derived for each species assuming LTE and excitation temperatures in the range 220-340 K for CH₃NH₂, 70-110 K for the CH₃CN isotopologues, and 120-215 K for NH2CHO and CH2NH. We report the first detections of CH3NH2 towards NGC 6334I with column density ratios with respect to CH₃OH of 5.9×10⁻³, 1.5×10⁻³, and 5.4×10⁻⁴ for the three hot cores MM1, MM2, and MM3, respectively. These values are slightly lower than the values derived for Sgr B2 but higher by more than order of magnitude as compared with the values derived for the low-mass protostar IRAS 16293-2422B. The detections of CH₃NH₂ in the hot cores of NGC 6334I hint that CH₃NH₂ is generally common in the interstellar medium, albeit high-sensitivity observations are essential for its detection. The good agreement between model predictions of CH₃NH₂ ratios and the observations towards NGC 6334I indicate a main formation pathway via radical recombination on grain surfaces.