Structural and Dynamical Analysis of the Quiescent Molecular Ridge in the Large Magellanic Cloud

We present a comparison of low-J (CO)-C-13 and CS observations of four different regions in the LMC-the quiescent Molecular Ridge, 30 Doradus, N159, and N113, all at a resolution of similar to 3 pc. The regions 30 Dor, N159, and N113 are actively forming massive stars, while the Molecular Ridge is forming almost no massive stars, despite its large reservoir of molecular gas and proximity to N159 and 30 Dor. We segment the emission from each region into hierarchical structures using dendrograms and analyze the sizes, masses, and line widths of these structures. We find that the Ridge has significantly lower kinetic energy at a given size scale and also lower surface densities than the other regions, resulting in higher virial parameters. This suggests that the Ridge is not forming massive stars as actively as the other regions because it has less dense gas and not because collapse is suppressed by excess kinetic energy. We also find that these physical conditions and energy balance vary significantly within the Ridge and that this variation appears only weakly correlated with distance from sites of massive-star formation such as R136 in 30 Dor, which is similar to 1 kpc away. These variations also show only a weak correlation with local star formation activity within the clouds.

Automated summary

In this study, a comparison is presented between low-J (CO)-C-13 and CS observations of four different regions in the LMC. It is found that the quiescent Molecular Ridge has lower kinetic energy and surface densities compared to the actively forming massive star regions of 30 Dor, N159, and N113. These differences suggest that the Molecular Ridge is less actively forming massive stars due to its less dense gas rather than excess kinetic energy suppressing collapse. Furthermore, variations in physical conditions and energy balance are observed within the Molecular Ridge, weakly correlated with distance from sites of massive star formation and local star formation activity within the clouds.