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The Lazy Giants: APOGEE Abundances Reveal Low Star Formation Efficiencies in the Magellanic Clouds
Department of Physics, Montana State University, P.O. Box 173840, Bozeman, 59717-3840, MT, United States; NSF's National Optical-Infrared Astronomy Research Laboratory, 950 North Cherry Avenue, Tucson, 85719, AZ, United States.
Department of Physics and Astronomy, University of Utah, Salt Lake City, 84112, UT, United States.
Department of Astronomy, University of Virginia, Charlottesville, 22904, VA, United States.ORCID iD: 0000-0003-2969-2445
Department of Astronomy, University of Texas at Austin, 2515 Speedway Boulevard, Austin, 78712, TX, United States.
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2020 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 895, no 2Article in journal (Refereed) Published
Abstract [en]

We report the first APOGEE metallicities and alpha-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 [alpha/Fe]-[Fe/H] distribution is very flat over a large metallicity range but rises by similar to 0.1 dex at -1.0 < [Fe/H] less than or similar to -0.5. 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." At the metal-poor end, we capture the increase of [alpha/Fe] with decreasing [Fe/H] and constrain the "alpha-knee" to [Fe/H] less than or similar to -2.2 in both MCs, implying a low star formation efficiency of similar to 0.01 Gyr(-1). The MC knees are more metal-poor than those of less massive MW dwarf galaxies such as Fornax, Sculptor, 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's gravitational potential only recently.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2020. Vol. 895, no 2
Keywords [en]
Magellanic Clouds, Galaxy abundances, Local Group, Surveys, Star formation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:mau:diva-17711DOI: 10.3847/1538-4357/ab7305ISI: 000538817000001Scopus ID: 2-s2.0-85086259241OAI: oai:DiVA.org:mau-17711DiVA, id: diva2:1453994
Available from: 2020-07-14 Created: 2020-07-14 Last updated: 2024-06-17Bibliographically approved

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Jönsson, Henrik

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Hayes, Christian R.Anguiano, BorjaJönsson, Henrik
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