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Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk | Michael R. Hayden
; Jo Bovy
; Jon A. Holtzman
; David L. Nidever
; Jonathan C. Bird
; David H. Weinberg
; Brett H. Andrews
; Carlos Allende Prieto
; Friedrich Anders
; Timothy C. Beers
; Dmitry Bizyaev
; Cristina Chiappini
; Katia Cunha
; Peter Frinchaboy
; Domingo A. García-Herńandez
; Ana E. García Pérez
; Léo Girardi
; Paul Harding
; Fred R. Hearty
; Jennifer A. Johnson
; Steven R. Majewski
; Szabolcs Mészáros
; Ivan Minchev
; Robert O'Connell
; Kaike Pan
; Annie C.Robin
; Ricardo P. Schiavon
; Donald P. Schneider
; Mathias Schultheis
; Matthew Shetrone
; Michael Skrutskie
; Matthias Steinmetz
; Verne Smith
; Olga Zamora
; Gail Zasowski
; | Date: |
7 Mar 2015 | Abstract: | Using a sample of 69,919 red giants from the SDSS-III/APOGEE Data Release 12,
we measure the distribution of stars in the [$alpha$/Fe] vs. [Fe/H] plane and
the metallicity distribution functions (MDF) across an unprecedented volume of
the Milky Way disk, with radius $3<R<15$ kpc and height $|z|<2$ kpc. Stars in
the inner disk ($R<5$ kpc) lie along a single track in [$alpha$/Fe] vs.
[Fe/H], starting with $alpha$-enhanced, metal-poor stars and ending at
[$alpha$/Fe]$sim0$ and [Fe/H]$sim+0.4$. At larger radii we find two distinct
sequences in [$alpha$/Fe] vs. [Fe/H] space, with a roughly solar-$alpha$
sequence that spans a decade in metallicity and a high-$alpha$ sequence that
merges with the low-$alpha$ sequence at super-solar [Fe/H]. The location of
the high-$alpha$ sequence is nearly constant across the disk, however there
are very few high-$alpha$ stars at $R>11$ kpc. The peak of the midplane MDF
shifts to lower metallicity at larger $R$, reflecting the Galactic metallicity
gradient. Most strikingly, the shape of the midplane MDF changes systematically
with radius, with a negatively skewed distribution at $3<R<7$ kpc, to a roughly
Gaussian distribution at the solar annulus, to a positively skewed shape in the
outer Galaxy. For stars with $|z|>1$ kpc or [$alpha$/Fe]$>0.18$, the MDF shows
little dependence on $R$. The positive skewness of the outer disk MDF may be a
signature of radial migration; we show that blurring of stellar populations by
orbital eccentricities is not enough to explain the reversal of MDF shape but a
simple model of radial migration can do so. | Source: | arXiv, 1503.2110 | Services: | Forum | Review | PDF | Favorites |
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