TY - JOUR
T1 - Metallicity gradients in the Milky Way disk as observed by the segue survey
AU - Cheng, Judy Y.
AU - Rockosi, Constance M.
AU - Morrison, Heather L.
AU - Schönrich, Ralph A.
AU - Lee, Young Sun
AU - Beers, Timothy C.
AU - Bizyaev, Dmitry
AU - Pan, Kaike
AU - Schneider, Donald P.
PY - 2012/2/20
Y1 - 2012/2/20
N2 - The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides a powerful constraint on the chemical enrichment and dynamical history of the disk system. We present the radial metallicity gradient, Δ[Fe/H]/ΔR, as a function of height above the plane, |Z|, using 7010 main-sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 kpc < R < 16kpc, 0.15 kpc < |Z| < 1.5kpc. The data reveal that the radial metallicity gradient becomes flat at heights |Z| > 1kpc. The median metallicity at large |Z| is consistent with the metallicities seen in outer disk open clusters, which exhibit a flat radial gradient at [Fe/H] ∼-0.5. We note that the outer disk clusters are also located at large |Z|; because the flat gradient extends to small R for our sample, there is some ambiguity in whether the observed trends for clusters are due to a change in R or |Z|. We therefore stress the importance of considering both the radial and vertical directions when measuring spatial abundance trends in the disk. The flattening of the gradient at high |Z| also has implications on thick disk formation scenarios, which predict different metallicity patterns in the thick disk. A flat gradient, such as we observe, is predicted by a turbulent disk at high redshift, but may also be consistent with radial migration, as long as mixing is strong. We test our analysis methods using a mock catalog based on the model of Schönrich & Binney, and we estimate our distance errors to be ∼25%. We also show that we can properly correct for selection biases by assigning weights to our targets.
AB - The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides a powerful constraint on the chemical enrichment and dynamical history of the disk system. We present the radial metallicity gradient, Δ[Fe/H]/ΔR, as a function of height above the plane, |Z|, using 7010 main-sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 kpc < R < 16kpc, 0.15 kpc < |Z| < 1.5kpc. The data reveal that the radial metallicity gradient becomes flat at heights |Z| > 1kpc. The median metallicity at large |Z| is consistent with the metallicities seen in outer disk open clusters, which exhibit a flat radial gradient at [Fe/H] ∼-0.5. We note that the outer disk clusters are also located at large |Z|; because the flat gradient extends to small R for our sample, there is some ambiguity in whether the observed trends for clusters are due to a change in R or |Z|. We therefore stress the importance of considering both the radial and vertical directions when measuring spatial abundance trends in the disk. The flattening of the gradient at high |Z| also has implications on thick disk formation scenarios, which predict different metallicity patterns in the thick disk. A flat gradient, such as we observe, is predicted by a turbulent disk at high redshift, but may also be consistent with radial migration, as long as mixing is strong. We test our analysis methods using a mock catalog based on the model of Schönrich & Binney, and we estimate our distance errors to be ∼25%. We also show that we can properly correct for selection biases by assigning weights to our targets.
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U2 - 10.1088/0004-637X/746/2/149
DO - 10.1088/0004-637X/746/2/149
M3 - Article
AN - SCOPUS:84863115433
SN - 0004-637X
VL - 746
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 149
ER -