THE COS/UVES ABSORPTION SURVEY OF THE MAGELLANIC STREAM. I. ONE-TENTH SOLAR ABUNDANCES ALONG THE BODY OF THE STREAM
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Institut fuer Physik und Astronomie, Universitaet Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam (Germany)
- Department of Astronomy, University of Wisconsin-Madison, 475 North Charter St., Madison, WI 53706 (United States)
- Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
- Argelander-Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)
- Institute of Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia)
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
The Magellanic Stream (MS) is a massive and extended tail of multi-phase gas stripped out of the Magellanic Clouds and interacting with the Galactic halo. In this first paper of an ongoing program to study the Stream in absorption, we present a chemical abundance analysis based on HST/COS and VLT/UVES spectra of four active galactic nuclei (RBS 144, NGC 7714, PHL 2525, and HE 0056-3622) lying behind the MS. Two of these sightlines yield good MS metallicity measurements: toward RBS 144 we measure a low MS metallicity of [S/H] = [S II/H I] = -1.13 {+-} 0.16 while toward NGC 7714 we measure [O/H] = [O I/H I] = -1.24 {+-} 0.20. Taken together with the published MS metallicity toward NGC 7469, these measurements indicate a uniform abundance of Almost-Equal-To 0.1 solar along the main body of the Stream. This provides strong support to a scenario in which most of the Stream was tidally stripped from the SMC Almost-Equal-To 1.5-2.5 Gyr ago (a time at which the SMC had a metallicity of Almost-Equal-To 0.1 solar), as predicted by several N-body simulations. However, in Paper II of this series, we report a much higher metallicity (S/H = 0.5 solar) in the inner Stream toward Fairall 9, a direction sampling a filament of the MS that Nidever et al. claim can be traced kinematically to the Large Magellanic Cloud, not the Small Magellanic Cloud. This shows that the bifurcation of the Stream is evident in its metal enrichment, as well as its spatial extent and kinematics. Finally we measure a similar low metallicity [O/H] = [O I/H I] = -1.03 {+-} 0.18 in the v{sub LSR} = 150 km s{sup -1} cloud toward HE 0056-3622, which belongs to a population of anomalous velocity clouds near the south Galactic pole. This suggests these clouds are associated with the Stream or more distant structures (possibly the Sculptor Group, which lies in this direction at the same velocity), rather than tracing foreground Galactic material.
- OSTI ID:
- 22121798
- Journal Information:
- Astrophysical Journal, Vol. 772, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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