Misc,
The chemistry of the most metal-rich damped Lyman $\alpha$ systems at z$\sim2$ II. Context with the Local Group
(2015)cite arxiv:1507.08311Comment: Accepted for publication in MNRAS. 24 Pages, 10 Figures, 4 tables. Data compilations within tarball or available upon request (contact Trystyn Berg).
Abstract
Using our sample of the most metal-rich damped Lyman $\alpha$ systems (DLAs)
at z$\sim2$, and two literature compilations of chemical abundances in 341 DLAs
and 2818 stars, we present an analysis of the chemical composition of DLAs in
the context of the Local Group. The metal-rich sample of DLAs at z$\sim2$
probes metallicities as high as the Galactic disc and the most metal-rich dwarf
spheroidals (dSphs), permitting an analysis of many elements typically observed
in DLAs (Fe, Zn, Cr, Mn, Si, and S) in comparison to stellar abundances
observed in the Galaxy and its satellites (in particular dSphs). Our main
conclusions are: (1) non-solar Zn/Fe abundances in metal-poor Galactic stars
and in dSphs over the full metallicity range probed by DLAs, suggest that Zn is
not a simple proxy for Fe in DLAs and therefore not a suitable indicator of
dust depletion. After correcting for dust depletion, the majority of DLAs have
subsolar Zn/Fe similar to dSphs; (2) at Fe/H$\sim-0.5$, a constant
Mn/Fe$\sim-0.5$ and near-solar $\alpha$/Fe (requiring an assumption about
dust depletion) are in better agreement with dwarf galaxies than Galactic disc
stars; (3) $\alpha$/Zn is usually solar or subsolar in DLAs. However,
although low ratios of $\alpha$/Fe are usually considered more `dwarf-like'
than `Milky Way-like', subsolar Zn/Fe in Local Group dwarfs leads to
supersolar $\alpha$/Zn in the dSphs, in contrast with the DLAs. Therefore,
whilst DLAs exhibit some similarities with the Local Group dwarf population,
there are also notable differences.
