We report the first APOGEE metallicities and \alpha -abundances measured for 3800 red giant stars spanning a large radial range of both the Large ( LMC ) and Small Magellanic Clouds ( SMC ) , the largest Milky Way dwarf galaxies .
Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances .
These are the first results presented that make use of the newly installed southern APOGEE instrument at the du Pont telescope at Las Campanas Observatory .
Our unbiased sample of the LMC spans a large range in metallicity from [ Fe/H ] = - 0.2 to very metal poor stars of [ Fe/H ] = - 2.5 , the most metal-poor Magellanic Clouds ( MCs ) stars detected to date .
The LMC [ \alpha /Fe ] – [ Fe/H ] distribution is very flat over a large metallicity range but rises by \sim 0.1 dex at the metal-rich end .
We interpret this as a sign of the known recent increase in MC star formation activity and are able to reproduce the pattern with a chemical evolution model that includes a recent “ starburst ” .
This starburst phase is required to reproduce the flat \alpha abundance distributions in both the LMC and SMC .
At the metal-poor end , we capture the increase of [ \alpha /Fe ] with decreasing [ Fe/H ] and constrain the “ \alpha -knee ” to [ Fe/H ] \lesssim - 2.2 in both MCs implying a low SFE of \sim 0.01 Gyr ^ { -1 } .
Counter-intuitively , the knee is more metal-poor than that of less massive Milky Way ( MW ) dwarf galaxies such as Fornax or Sagittarius .
One possible interpretation is that the MCs formed in a lower-density environment than the MW , a hypothesis that is consistent with the paradigm that the MCs fell into the MW potential only recently .