The Lazy Giants: APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic Clouds

Abstract

We report the first APOGEE metallicities and α -element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky Way (MW) 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 on 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 with [Fe/H] ≈ −2.5, the most metal-poor Magellanic Cloud (MC) stars detected to date. The LMC [ α /Fe]–[Fe/H] distribution is very flat over a large metallicity range but rises by ∼0.1 dex at −1.0