Hot cores in the outer Galaxy: impact of metallicity on the formation of complex organic molecules

Many complex organic molecules (COMs) in star forming regions are believed to form on the surfaces of dust grains or in their ice mantles. Therefore, we expect both the reduced metallicity and dust-to-gas ratio in the outer Galaxy to have an impact on the chemical composition of these regions. To test this, we use NOEMA to perform an imaging spectral line survey of the hot core candidate G135.27+2.79 at a galactocentric distance of 13.1 kpc. Our NOEMA observations in the 1.3 mm range have led to the identification of 43 species, including their isotopologues and deuterated variants. Among these are COMs with up to nine atoms, detected toward a hot (>100 K) and compact (< 5000 au) region. These detections confirm G135.27+2.79 as the second known hot core in the outer Galaxy. The rotational temperatures and column densities of the detected molecules are derived under the LTE approximation. Hot-core simulations with the three-phase astrochemical code MAGICKAL with reduced metallicity and dust-to-gas ratio and under normal conditions predict that certain molecules have a significantly reduced abundance (relative to methanol) at low metallicity and dust-to-gas ratio while others keep a similar abundance. The model predictions are approximately consistent with our observations when we compare the COM abundances of G135.27+2.79 with those in hot cores/corinos within the Solar circle, suggesting that metallicity and dust-to-gas ratio do have an impact on the formation of COMs.