Observational Evidence from SDSS for a Merger Origin of the Milky Way's Thick Disk

Understand

We test competing models that aim at explaining the nature of stars in the Milky Way that are well away (|z|$\gtrsim$ 1kpc) from the midplane, the so-called thick disk: the stars may have gotten there through orbital migration, through satellite mergers and accretion, or through heating of pre-existing thin disk stars.

• Sales et al.
• (2009) proposed the eccentricity distribution of thick disk stars as a diagnostic to differentiate between these mechanisms.
• Drawing on SDSS DR7, we have assembled a sample of 34,223 G-dwarfs with 6-D phase-space information and metallicities, and have derived orbital eccentricities for them.