Title Renegades in the Solar neighborhood Ana Bonaca ITC Fellow Harvard University // Charlie Conroy // // Andrew Wetzel //
Origin of the halo stars: In situ Eggen, Lynden-Bell & Sandage (1962) Accretion Searle & Zinn (1978)
Origin of the halo stars: In situ Eggen, Lynden-Bell & Sandage (1962) Accretion Searle & Zinn (1978) Fraction of total halo 1.0 0.8 0.6 0.4 0.2 0.0 0 50 100 150 200 Distance (kpc) Fraction of total halo 1.0 0.8 0.6 0.4 Zolotov et al. (2009) Recent accretion Ancient accretion 0.2 In situ 0.0 0 50 100 150 200 Distance (kpc)
Goal: Goal Explore the structure of the local stellar halo, in hope of finding clues to its origin.
Exploring the Galactic 6-D phase space with: z Gaia / TGAS Brown et al. (2016) Michalik et al. (2015) x RAVE / RAVE-on Kunder et al. (2017) Casey et al. (2016)
Kinematic disk / halo decomposition
Kinematic disk / halo decomposition Halo: Halo Disk
Metallicity distribution function 2.0 1.5 Disk Halo Probability 1.0 0.5 0.0-2 -1 0 [Fe/H]
Metallicity distribution function 2.0 1.5 Disk Halo Probability 1.0 0.5 0.0-2 -1 0 [Fe/H] There are a lot of metal-rich stars in the halo.
Metallicity distribution function RAVE-on APOGEE 2.0 1.5 Disk Halo 1.5 Probability 1.0 Probability 1.0 0.5 0.5 0.0-2 -1 0 [Fe/H] 0.0-2 -1 0 [Fe/H] There are a lot of metal-rich stars in the halo.
Chemical abundance patterns Metal rich halo follows the disk abundance pattern.
Orientation of angular momenta z x
Orientation of angular momenta z Angular momentum orientation angle: x
Orientation of angular momenta z Angular momentum orientation angle: 0.05 Disk x 0.04 Halo: [Fe/H] > 1 Halo: [Fe/H] 1 Probability 0.03 0.02 Metal-rich halo is preferentially prograde. 0.01 0.00 0 50 100 150 L orientation (deg)
Toy model of the Galaxy positions: TGAS + RAVE-on velocities: Bensby et al. (2003)
Toy model of the Galaxy positions: TGAS + RAVE-on velocities: Bensby et al. (2003)
Toy model of the Galaxy positions: TGAS + RAVE-on velocities: Bensby et al. (2003)
Toy model of the Galaxy positions: TGAS + RAVE-on velocities: Bensby et al. (2003)
Toy halo, kinematically defined
Toy halo, kinematically defined The metal poor halo is isotropic.
Toy halo, kinematically defined The metal poor halo is isotropic.
Halo origin hypotesis Metal-poor halo: isotropic, hence accreted Metal-rich halo: preferentially prograde, hence formed in situ
Milky Way vs Latte ~ Milky Way Latte Wetzel et al. (2016)
Milky Way vs Latte ~ Milky Way Latte Wetzel et al. (2016)
The Milky Way / Latte comparison
The Milky Way / Latte comparison
The Milky Way / Latte comparison
The origin of Solar neighborhood in Latte
The origin of Solar neighborhood in Latte
The origin of Solar neighborhood in Latte Most halo stars migrated to the Solar neighborhood.
The origin of Solar neighborhood in Latte Most halo stars migrated to the Solar neighborhood.
Halo origin from stellar ages Latte prediction: At a given age, the in situ halo is more metal rich than the accreted halo.
Halo origin from stellar ages Apply! Gaia Sprint 2017 Heidelberg http://gaia.lol Latte prediction: At a given age, the in situ halo is more metal rich than the accreted halo.
Summary Stellar halo in the Solar neighborhood has an isotropic, metal-poor component, and a prograde, metal-rich component.
Stellar Summary halo in the Solar neighborhood has an isotropic, metal-poor component, and a prograde, metal-rich component. Comparison to simulations suggests an accretion origin for the metal-poor, and an in situ origin for the metal-rich component.