TY - JOUR
T1 - Formation and evolution of the disk system of the milky way
T2 - [α/Fe] ratios and kinematics of the segue G-dwarf sample
AU - Lee, Young Sun
AU - Beers, Timothy C.
AU - An, Deokkeun
AU - Ivezić, Željko
AU - Just, Andreas
AU - Rockosi, Constance M.
AU - Morrison, Heather L.
AU - Johnson, Jennifer A.
AU - Schönrich, Ralph
AU - Bird, Jonathan
AU - Yanny, Brian
AU - Harding, Paul
AU - Rocha-Pinto, Helio J.
PY - 2011/9/10
Y1 - 2011/9/10
N2 - We employ measurements of the [α/Fe] ratio derived from low-resolution (R 2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate them into likely thin- and thick-disk subsamples. Both subsamples exhibit strong gradients of orbital rotational velocity with metallicity, of opposite signs, -20 to -30kms-1dex-1 for the thin-disk and +40 to +50kms-1dex-1 for the thick-disk population. The rotational velocity is uncorrelated with Galactocentric distance for the thin-disk subsample and exhibits a small trend for the thick-disk subsample. The rotational velocity decreases with distance from the plane for both disk components, with similar slopes (-9.0 1.0kms-1kpc-1). Thick-disk stars exhibit a strong trend of orbital eccentricity with metallicity (about -0.2 dex-1), while the eccentricity does not change with metallicity for the thin-disk subsample. The eccentricity is almost independent of Galactocentric radius for the thin-disk population, while a marginal gradient of the eccentricity with radius exists for the thick-disk population. Both subsamples possess similar positive gradients of eccentricity with distance from the Galactic plane. The shapes of the eccentricity distributions for the thin- and thick-disk populations are independent of distance from the plane, and include no significant numbers of stars with eccentricity above 0.6. Among several contemporary models of disk evolution that we consider, radial migration appears to have played an important role in the evolution of the thin-disk population, but possibly less so for the thick disk, relative to the gas-rich merger or disk heating scenarios. We emphasize that more physically realistic models and simulations need to be constructed in order to carry out the detailed quantitative comparisons that our new data enable.
AB - We employ measurements of the [α/Fe] ratio derived from low-resolution (R 2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate them into likely thin- and thick-disk subsamples. Both subsamples exhibit strong gradients of orbital rotational velocity with metallicity, of opposite signs, -20 to -30kms-1dex-1 for the thin-disk and +40 to +50kms-1dex-1 for the thick-disk population. The rotational velocity is uncorrelated with Galactocentric distance for the thin-disk subsample and exhibits a small trend for the thick-disk subsample. The rotational velocity decreases with distance from the plane for both disk components, with similar slopes (-9.0 1.0kms-1kpc-1). Thick-disk stars exhibit a strong trend of orbital eccentricity with metallicity (about -0.2 dex-1), while the eccentricity does not change with metallicity for the thin-disk subsample. The eccentricity is almost independent of Galactocentric radius for the thin-disk population, while a marginal gradient of the eccentricity with radius exists for the thick-disk population. Both subsamples possess similar positive gradients of eccentricity with distance from the Galactic plane. The shapes of the eccentricity distributions for the thin- and thick-disk populations are independent of distance from the plane, and include no significant numbers of stars with eccentricity above 0.6. Among several contemporary models of disk evolution that we consider, radial migration appears to have played an important role in the evolution of the thin-disk population, but possibly less so for the thick disk, relative to the gas-rich merger or disk heating scenarios. We emphasize that more physically realistic models and simulations need to be constructed in order to carry out the detailed quantitative comparisons that our new data enable.
KW - Galaxy: disk
KW - Galaxy: formation
KW - Galaxy: kinematics and dynamics
KW - Galaxy: structure
UR - http://www.scopus.com/inward/record.url?scp=80052795246&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/738/2/187
DO - 10.1088/0004-637X/738/2/187
M3 - Article
AN - SCOPUS:80052795246
SN - 0004-637X
VL - 738
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 187
ER -