This Joint Legacy Program, LMC+, aims to determine the role of metallicity on the physical conditions of the molecular, atomic, and ionised interstellar medium, by zooming into a large region of the Magellanic Cloud that is known to have a factor of 2 lower metal abundance than the Milky Way.
We propose a 1.3 deg x 0.5 deg FIFI-LS map of [CII] 158 micron and [OIII] 88 micron emission toward the most prominent large-scale star forming/molecular cloud complex in the LMC, the Southern Molecular Ridge. These far-infrared lines trace the molecular gas not traced by CO-emission (the CO-dark gas) as well as ionized gas in embedded and bursting HII regions. Even though a change in metallicity by a factor of 2 seems small, we expect to detect a factor 10 or more molecular gas mass than that seen in CO, which will be photodissociated by the LMC interstellar radiation field. The CO-gas will be in dense clumpy molecular pockets, permeated by lower density neutral interstellar medium.
We will determine the mass ratio of dense molecular and more diffuse molecular/atomic gas and the porosity of the interstellar medium. This is significant, in order to estimate the star formation efficiency in the LMC and also to relate to the structure of the interstellar medium in high-redshift galaxies where the average metallicity is below solar.
Only this large-scale SOFIA FIFI-LS map of this template region can bring to light the full interplay of star formation and molecular gas destruction by massive stellar radiative and wind feedback.
Much of this region has recently been targeted by ALMA CO observations, to allow the comparison between conditions for the role of CO-bright vs CO-dark molecular reservoirs. This survey may also serve as a pathfinder for higher spectral resolution upGREAT observations, and observations of the energetic mid-infrared nebular species with JWST.
