Understanding the formation of complex organic molecules (COMs) in star forming regions is crucial for astrochemistry. Many COMs are believed to form on the surfaces of dust grains or in their ice mantles. The metallicity and dust-to-gas mass ratio in the outer Galaxy are lower than in the inner regions and are expected to influence the chemical composition of star-forming environments. To test this, we used the NOEMA interferometer to conduct a sensitive imaging spectral line survey of a hot core candidate located at a galactocentric distance of 13 kpc.

We identified 43 molecular species in the spectrum of this source, including less abundant isotopologs and deuterated species. Among them, 12 COMs containing up to ten atoms were detected in a compact (<5000 au), hot (>100 K) region. These findings confirm this source as a new hot core in the outer Galaxy, providing an excellent opportunity to study COM formation under low-metallicity conditions.

We derived rotational temperatures and column densities of the detected molecules and compared our results with simulations performed with the three-phase astrochemical code MAGICKAL. The models predict that certain molecules exhibit significantly reduced abundances (relative to methanol) at low metallicity and dust-to-gas mass ratio, while the abundances of other species remain relatively unchanged. Our observations are broadly consistent with these predictions when comparing COM abundances in this source to those in hot cores and hot corinos in the inner Galaxy. These results suggest that metallicity and the dust-to-gas mass ratio have an impact on the formation of COMs (paper in preparation).

Figure caption: part of the NOEMA spectral line survey of the new hot core in the outer Galaxy. The contributions of selected molecules to the observed spectrum are shown in various colors.