2013ApJ...772..111R
The COS/UVES Absorption Survey of the Magellanic Stream. II. Evidence for a Complex Enrichment History of the Stream from the Fairall 9 Sightline
Richter, Philipp ( Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, D-14476 Golm (Potsdam), Germany ; Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany ); Fox, Andrew J. ( Space Telescope Science Institute, Baltimore, MD 21218, USA ); Wakker, Bart P. ( Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706, USA ); Lehner, Nicolas ( Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556, USA ); Howk, J. Christopher ( Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556, USA ); Bland-Hawthorn, Joss ( Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia ); Ben Bekhti, Nadya ( Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany ); Fechner, Cora ( Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, D-14476 Golm (Potsdam), Germany ) show affiliations
The Astrophysical Journal, Volume 772, Issue 2, article id. 111, 19 pp. (2013).
Published in Aug 2013
We present a multi-wavelength study of the Magellanic Stream (MS), a massive gaseous structure in the Local Group that is believed to represent material stripped from the Magellanic Clouds. We use ultraviolet, optical and radio data obtained with HST/COS, VLT/UVES, FUSE, GASS, and ATCA to study metal abundances and physical conditions in the Stream toward the quasar Fairall 9. Line absorption in the MS from a large number of metal ions and from molecular hydrogen is detected in up to seven absorption components, indicating the presence of multi-phase gas. From the analysis of unsaturated S II absorption, in combination with a detailed photoionization model, we obtain a surprisingly high α abundance in the Stream toward Fairall 9 of [S/H] = -0.30 ± 0.04 (0.50 solar). This value is five times higher than what is found along other MS sightlines based on similar COS/UVES data sets. In contrast, the measured nitrogen abundance is found to be substantially lower ([N/H] = -1.15 ± 0.06), implying a very low [N/α] ratio of -0.85 dex. The substantial differences in the chemical composition of MS toward Fairall 9 compared to other sightlines point toward a complex enrichment history of the Stream. We favor a scenario, in which the gas toward Fairall 9 was locally enriched with α elements by massive stars and then was separated from the Magellanic Clouds before the delayed nitrogen enrichment from intermediate-mass stars could set in. Our results support (but do not require) the idea that there is a metal-enriched filament in the Stream toward Fairall 9 that originates in the LMC.Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by the Space Telescope Science Institute (STScI) for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5D26555, and on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile under Program ID 085.C-0172(A).
Keywords:
Free Keywords: Astrophysics - Galaxy Astrophysics; Galaxy: evolution; Galaxy: halo; ISM: abundances; Magellanic Clouds; quasars: absorption lines
Astronomy: Galaxy: evolution; Galaxy: halo; ISM: abundances; Magellanic Clouds; quasars: absorption lines
arXiv: Astrophysics - Galaxy Astrophysics
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