Presentation #348.07 in the session “Star Formation”.
The Large Magellanic Cloud (LMC) is the nearest star-forming galaxy with a sub-solar metallicity, making it a useful laboratory for detailed investigations on the formation and survival of complex organic molecules (COMs). In our previous study, we revealed the presence of COMs more complex than CH3OH in two hot cores (small, hot, and dense regions around the forming massive stars) in the N113 star-forming region in the LMC; these hot cores are the only extragalactic sources exhibiting the hot core complex chemistry reported in literature. One hot core without COMs has previously been observed in the LMC. To increase a sample of hot cores in the LMC and enable statistical studies, we conducted observations with the Atacama Large Millimeter/submillimeter Array (ALMA) toward seven fields in the LMC having common characteristics with two known hot cores with COMs, covering four 1875-MHz spectral windows between ~241 GHz and ~261 GHz. Here we report the results of the analysis of three ALMA fields, all located in the N105 star-forming region. N105 lies at the western edge of the LMC bar with the on-going star formation traced by H2O, OH, and CH3OH masers, ultracompact (UC) H II regions, and young stellar objects.
The analysis of the N105 data reveals twelve 1.2 mm continuum sources with a range of chemical make-ups, including two hot cores and one UC HII region. The CH3OH emission is widespread with an extended cold component and compact emission toward all continuum sources. COMs CH3CN and CH3OCH3 are detected toward two hot cores in N105 together with smaller molecules such SO2, SO, or HNCO (typically found in Galactic hot cores). We also report a probable (six sigma) detection of a single line of the astrobiologically relevant formamide molecule (NH2CHO) toward one of the hot cores and the detection of higher-order hydrogen recombination lines toward the UC HII region. This is the first detection of NH2CHO in a sub-solar metallicity environment and the first extragalactic detection of higher-order hydrogen recombination lines. We compare the molecular abundances measured toward hot cores in N105 with those observed toward Galactic hot cores to investigate an impact of a reduced metallicity on the hot core chemistry. The metallicity of the LMC is similar to galaxies at the peak of star formation in the Universe (redshift z~1.5), making it an ideal template for studying star formation and complex chemistry in low-metallicity systems at earlier cosmological epochs.