Formation And Evolution Of The Disk System Of The Milky Way: [α/Fe] Ratios And Kinematics Of The SEGUE G-dwarf Sample

Details Formation And Evolution Of The Disk System Of The Milky Way: [α/Fe] Ratios And Kinematics Of The SEGUE G-dwarf Sample Formation And Evolution Of The Disk System Of The Milky Way: [α/Fe] Ratios And Kinematics Of The SEGUE G-dwarf Sample

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21823102b&link_type=abstract

American Astronomical Society, AAS Meeting #218, #231.02; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the derived local kinematics for a sample of some 17,500 G-type dwarfs in the solar neighborhood, and compare with the rotational velocity gradients on metallicity, the radial and vertical velocity gradients, and the stellar orbital eccentricity distributions predicted by contemporary models for the formation and evolution of the Milky Way's disk system. The sample is culled from an original total of some 63,000 G dwarf candidates having available low-resolution (R = 2000) spectra, ugriz photometry, proper motions, and the latest stellar atmospheric parameter estimates (Teff, log g, [Fe/H]) from the eighth public release of the Sloan Digital Sky Survey. Using estimates for [α/Fe] as a reference, we divide our local dwarf sample within |Z| < 3 kpc from the Galactic plane and 7 < R < 10 kpc into likely thin-disk and thick-disk components. The thin-disk subsample exhibits a strong gradient in observed rotational velocity with [Fe/H] (-22 km/s/dex), which contrasts with expectations from classical local chemical evolution models. The thick-disk subsample exhibits a small slope in rotational velocity with distance from the Galactic center (-5.6 km/s/kpc), in line with expectations from gas-rich merger models. The observed distribution of orbital eccentricities for our thick-disk subsample is also in better agreement with gas-rich merger models for the origin of the thick disk, rather than arising (solely) due to radial migration or pure accretion. Based on these results we propose that, while radial migration appears to have played an important role in the evolution of the thin-disk population, it may be less important than gas-rich mergers or thin-disk heating in the formation of the thick disk.

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