Hot Core Chemistry and Star Formation in the Outer Galaxy

ABSTRACT :
The outer part of the Galaxy is a suitable region to investigate the star forming processes and chemical evolution in the early Galaxy because of its low metallicity nature. We here present the second detection of a hot molecular core associated with a protostar and the first detection of spatially resolved protostellar jets in the outer Galaxy. In this work, we carried out ALMA observations toward the five protostar candidates located in the outer Galaxy star forming region (Sharpless 2-283, Galactocentric distance about 15.7 kpc). We have identified one protostar associated with a variety of molecular species (CO, HCO+, H13CO+, HCOOH, SO, SO+, SO2, SiO, NS, H13CN, HC15N and D2CO) including complex organic molecules (CH3OH, 13CH3OH, CH2DOH and CH3OCH3). Moreover, we have detected bipolar outflows and jets with CO and SiO emission line and this is the first time that such protostellar jets are spatially resolved in a low-metallicity environment. The physical characteristics (e.g., morphology, jet bullet interval, and dynamical timescale) of the observed outflows and jets resemble those observed in nearby low-mass star forming regions.
A comparison of fractional abundances of molecular species relative to CH3OH between this protostar and the previously detected protostar in the outer Galaxy (WB89-789 SMM1; Shimonishi et al. 2021) shows a great similarity. The results would indicate that organic molecules may be ubiquitously produced in low-metallicity environments of the outer Galaxy, and their chemical compositions roughly follow the metallicity scaling law. On the other hand, the fractional abundance of SiO relative to CO in the jet is an order of magnitude less than that observed in a normal metallicity counterpart. This would indicate that the dust compositions in the low-metallicity environments are different from those in normal metallicity environments.