The detection of a hot molecular core in the extreme outer Galaxy

Abstract: Interstellar chemistry in low metallicity environments is crucial to understand chemical processes in the past metal-poor universe. Recent studies of interstellar molecules in nearby low-metallicity galaxies have suggested that the metallicity has a significant effect on chemistry of star-forming cores. Here we report the first detection of a hot molecular core in the extreme outer Galaxy, which is an excellent laboratory to study star formation and interstellar medium in a Galactic low-metallicity environment. The target star-forming region, WB89-789, is located at the galactocentric distance of 19 kpc. Our ALMA observations in 241-246, 256-261, 337-341, and 349-353 GHz have detected a variety of carbon-, oxygen-, nitrogen-, sulfur-, and silicon-bearing species, including complex organic molecules (COMs) containing up to nine atoms, towards a warm (>100 K) and compact (<0.03 pc) region associated with a protostar (~8x10^3 L_sun). Deuterated species such as HDO, HDCO, D2CO, and CH2DOH are also detected. A comparison of fractional abundances of COMs relative to CH3OH between the outer Galactic hot core and an inner Galactic counterpart shows a remarkable similarity. On the other hand, the molecular abundances in the present source do not resemble those of low-metallicity hot cores in the Large Magellanic Cloud. The results suggest that a great molecular complexity exists even in a primordial environment of the extreme outer Galaxy. The detection of another embedded protostar associated with high-velocity SiO outflows is also reported.