Stellar spectroscopy , UBV photometry , H \alpha imaging , and analysis of data from the ATCA H i survey of the LMC are combined in a study of the LMC OB association LH 72 and its surroundings .
LH 72 lies on the rim of a previously identified H i shell , SGS-14 , and in the interior of LMC-4 , one of the LMC ’ s largest known supergiant shells .
Our analysis of the H i data finds that SGS-14 is expanding with velocity v _ { exp } \sim 15 km s ^ { -1 } , giving it an expansion age of \sim 15 Myr .
Through the stellar spectroscopy and photometry , we find similar ages for the oldest stars of LH 72 , \sim 15 - 30 Myr .
We confirm that LH 72 contains an age spread of \sim 15 - 30 Myr , similar to the range in ages of stars derived for the entire surrounding supergiant shell .
Combining analysis of the O and B stars with H \alpha imaging of the H ii region DEM 228 , we find that DEM 228 accounts for only 60 % of the available ionizing Lyman continuum photons .
Comparing the distribution of ionized gas with that of the H i , we find that DEM 228 and LH 72 are offset by \sim 1 - 2 \arcmin from the peak 21-cm emission , towards the interior of SGS-14 .
Taken together , these results imply that SGS-14 has cleared its interior of gas and triggered the formation of LH 72 .
On the basis of our results , we suggest that LMC-4 was not formed as unit but by overlapping shells such as SGS-14 , and that LH 72 will evolve to produce a stellar arc similar to others seen within LMC-4 .