Misc,
Chemical Cartography with APOGEE: Large-scale Mean Metallicity Maps of the Milky Way
(2013)cite arxiv:1311.4569Comment: 16 pages, 12 figures, submitted to AJ.
Abstract
We present Galactic mean metallicity maps derived from the first year of the
SDSS-III APOGEE experiment. Mean abundances in different zones of
Galactocentric radius (0 < R < 15 kpc) at a range of heights above the plane (0
< |z| < 3 kpc), are derived from a sample of nearly 20,000 stars with
unprecedented coverage, including stars in the Galactic mid-plane at large
distances. We also split the sample into subsamples of stars with low and
high-\alpha/M abundance ratios. We assess possible biases in deriving the
mean abundances, and find they are likely to be small except in the inner
regions of the Galaxy. A negative radial gradient exists over much of the
Galaxy; however, the gradient appears to flatten for R < 6 kpc, in particular
near the Galactic mid-plane and for low-\alpha/M stars. At R > 6 kpc, the
gradient flattens as one moves off of the plane, and is flatter at all heights
for high-\alpha/M stars than for low-\alpha/M stars. Alternatively,
these gradients can be described as vertical gradients that flatten at larger
Galactocentric radius; these vertical gradients are similar for both low and
high-\alpha/M populations. Stars with higher \alpha/M appear to have a
flatter radial gradient than stars with lower \alpha/M. This could suggest
that the metallicity gradient has grown steeper with time or, alternatively,
that gradients are washed out over time by migration of stars.
