THE COS/UVES ABSORPTION SURVEY OF THE MAGELLANIC STREAM. II. EVIDENCE FOR A COMPLEX ENRICHMENT HISTORY OF THE STREAM FROM THE FAIRALL 9 SIGHTLINE

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 meta...

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Bibliographic Details
Published in:The Astrophysical journal 2013-08, Vol.772 (2), p.1-19
Main Authors: Richter, Philipp, Fox, Andrew J, Wakker, Bart P, Lehner, Nicolas, Howk, J Christopher, Bland-hawthorn, Joss, BEKHTI, NADYA BEN, Fechner, Cora
Format: Article
Language:English
Subjects:
ABSORPTION
ABUNDANCE
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COMPLEXES
Enrichment
Filaments
Fuses
HYDROGEN
IONS
MAGELLANIC CLOUDS
METALS
NITROGEN
PHOTOIONIZATION
QUASARS
STARS
STREAMS
Ultraviolet
ULTRAVIOLET RADIATION
WAVELENGTHS
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Summary: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 multiphase gas. From the analysis of unsaturated S II absorption, in combination with a detailed photoionization model, we obtain a surprisingly high alpha abundance in the Stream toward Fairall 9 of [S/H] = -0.30 + or - 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 + or - 0.06), implying a very low [N/ alpha ] 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 alpha 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.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/772/2/111