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2013ApJ...772..111R - Astrophys. J., 772, 111 (2013/August-1)

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 P., FOX A.J., WAKKER B.P., LEHNER N., HOWK J.C., BLAND-HAWTHORN J., BEN BEKHTI N. and FECHNER C.

Abstract (from CDS):

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.

Abstract Copyright:

Journal keyword(s): Galaxy: evolution - Galaxy: halo - ISM: abundances - Magellanic Clouds - quasars: absorption lines

Simbad objects: 16

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