Molecular Development in the Large Magellanic Cloud

Using a new network and a new model, we have studied chemical complexity in cold portions of dense clouds of the Large Magellanic Cloud (LMC). We varied the hydrogen number density between 1 × 10⁵ and 5 × 10⁵ cm^-3 and, for each density, we ran models for A_V = 3, 5, and 10. Then, for each density and visual extinction we varied the grain temperature between 10 and 50 K in small intervals, while keeping the gas temperature constant at 20 K. We used a gas-to-dust mass ratio based on a variety of observations and analyses, and scaled the elemental abundances of the LMC so that they are representative of so-called “low” metallic abundances. We found that although the LMC is metal-poor, it still shows a rich chemistry; almost all the major observed species in the gas phase of our Galaxy should be detectable using present-day observational facilities. We compared our model results with observed gas-phase abundances in some cold and dense sources, and found reasonably good agreement for most species. We also found that some observed results, especially for methanol, are better matched if these regions currently possess lower temperatures, or possessed them in the past. Finally, we discussed our simulated abundances for H₂O ice with respect to total hydrogen, and CO₂, CO, CH₃OH, and NH₃ ices with respect to water ice, and compared our values with those for two observed ices—CO₂ and CO—detected in front of young stellar objects in the LMC.