FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [{alpha}/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE

Journal Article · Sat Sep 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/2/187; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21584844

Lee, Young Sun; Beers, Timothy C ^[1]; An, Deokkeun ^[2]; Ivezic, Zeljko ^[3]; Just, Andreas ^[4]; Rockosi, Constance M ^[5]; Morrison, Heather L; Harding, Paul ^[6]; Johnson, Jennifer A; Bird, Jonathan ^[7]; Schoenrich, Ralph ^[8]; Yanny, Brian ^[9]

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1. Department of Physics and Astronomy and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824 (United States)
2. Department of Science Education, Ewha Womans University, Seoul 120-750 (Korea, Republic of)
3. Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)
4. Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg (ZAH), Moenchhofstr. 12-14, 69120 Heidelberg (Germany)
5. UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
6. Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States)
7. Department of Astronomy, Ohio State University, Columbus, OH 43210 (United States)
8. Max-Planck-Institute fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)
9. Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States)

We employ measurements of the [{alpha}/Fe] ratio derived from low-resolution (R {approx} 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 -30 km s{sup -1} dex{sup -1} for the thin-disk and +40 to +50 km s{sup -1} dex{sup -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 {+-} 1.0 km s{sup -1} kpc{sup -1}). Thick-disk stars exhibit a strong trend of orbital eccentricity with metallicity (about -0.2 dex{sup -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.

• OSTI ID: 21584844
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 738; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELEMENTS
EVOLUTION
GALAXIES
IRON
IRON-ALPHA
METALS
MILKY WAY
MOTION
ROTATION
STARS
TRANSITION ELEMENTS
VELOCITY