Understanding how local conditions influence the H+-H0-H2 and the C+-C0-CO transitions in molecular clouds, particularly in low-metallicity environments, is crucial for deciphering the mechanisms driving star formation and the dynamics of the ISM. To this end, we present results from the SOFIA Legacy Program (LMC+), which mapped a 45’ x 20’ (660 pc x 300 pc) region of the southern molecular ridge in the Large Magellanic Cloud (LMC) at an unprecedented resolution of 2.5 pc. This study leverages the largest spectral map of the LMC obtained by SOFIA, including [CII] 158 μm and [OIII] 88 μm observations, along with ALMA CO data, to investigate the interplay between CO-bright and CO-dark gas reservoirs and the local conditions governing their distribution.
The [CII] emission, while peaking at prominent massive star-forming regions (N158, N159, N160), extends diffusely across the mapped region, contrasting sharply with the clumpier CO emission, which often does not spatially coincide with [CII]. Preliminary analyses reveal that the [CII]/CO ratio varies by several orders of magnitude across the region, highlighting significant heterogeneity in ISM conditions. Key questions we plan to address include: How do the properties and structure of ISM phases transition from dense star-forming regions to more diffuse, low-visual-extinction (A_v) environments? What local factors favor the formation of CO-dark versus CO-bright molecular gas?
Our study also explores the variations in heating and cooling processes in star-forming and quiescent regions of this low-metallicity environment, providing critical insights into the physics of photodissociation regions (PDRs) and molecular cloud evolution. These findings have far-reaching implications for understanding the ISM and star formation in the early universe, where [CII] 158 μm and [OIII] 88 μm emission lines are now frequently observed in high-redshift galaxies.