The Characterization of the Metal-rich Stellar Halo with Gaia DR2 - - PowerPoint PPT Presentation

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The Characterization of the Metal-rich Stellar Halo with Gaia DR2 - - PowerPoint PPT Presentation

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The Characterization of the Metal-rich Stellar Halo with Gaia DR2 and APOGEE Emma Fernndez-Alvar Edmundo Moreno, Jose Fernndez-Trincado, William J. Schuster, Leticia Carigi, Alejandra Recio-Blanco,... Stellar Halos Across the Cosmos 4 th

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The Characterization of the Metal-rich Stellar Halo with Gaia DR2 and APOGEE

Emma Fernández-Alvar Edmundo Moreno, Jose Fernández-Trincado, William J. Schuster, Leticia Carigi, Alejandra Recio-Blanco,...

Stellar Halos Across the Cosmos 4th July 2018

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Stellar populations in the halo

  • Halo stars: larger kinematical energy comparing to

disk stars

  • Within samples of halo stars: detection of different

chemical trends formed by distinct formation channels: In situ Accreted

(Steve Majewski’s talk)

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A dual formation scenario for the Galactic halo

  • Inner and outer halo differences:

spatial (Deason, Belokurov & Evans 2011), chemical (Fernández-Alvar et al. 2015,2017) and kinematical (Carollo et al. 2007, 2010; Belokurov et al. 2018; several talks here)

[Ca/Fe] Fernández-Alvar et al. (2015)

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The two alpha pop in the metal-rich halo

(In the solar neighbourhood) Nissen and Schuster (2010)

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The two alpha pop in the metal-rich halo

Hayes et al. (2018a): APOGEE database, much larger

halo sample

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The two alpha pop in the metal-rich halo

Fernández-Alvar et al. (2018)

Vrad > 180 km s-1

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The two alpha pop in the metal-rich halo

(In the solar neighbourhood)

Bonaca et al. (2017): in situ origin Helmi et al. (2018): accreted origin

Haywood et al. (2018)

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Our halo sample in APOGEE

  • |z|>5 kpc
  • 4000 < Teff < 6500 K
  • 1.5 < log g < 3.5
  • Chemical abundances by ASPCAP
  • Orbital parameters: GravPot16 (Fernández-Trincado et al. 2017)

– Vrad APOGEE (σ ~ 0.1 km/s) – Gaia DR2 proper motions – StarHorse Distances (Santiago et al. (in prep.) bayesian method from

spectroscopic stellar parameters and Gaia parallaxes priors).

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Metallicity Distribution Function

Fernández-Alvar et al. (in prep.)

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Fernández-Alvar et al. (in prep.) < E > Z m a x < L

z

>

Orbital Parameters

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< E > Z m a x < L

z

> Fernández-Alvar et al. (in prep.)

Orbital Parameters

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< E > Z m a x < L

z

> Fernández-Alvar et al. (in prep.)

Orbital Parameters

See Hayes et

  • al. (2018b)
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Fernández-Alvar et al (in prep.)

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Fernández-Alvar et al. (in prep.)

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Fernández-Alvar et al. (in prep.)

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Conclusions

  • Metal-rich halo detected at |z| > 5 kpc

Splits in three [Mg/Fe] vs. [Fe/H] sequences

  • Intermediate Mg/Fe stars:
  • KNEE of the high-alpha population
  • Triangulum/Andromeda candidates
  • Low-[Mg/Fe] stars follow the chemical trend of the bulk of metal-poor halo stars,

V distributed in 0 rotation, orbits less bound and reach larger zmax, rmax and rmin: accreted origin

  • High-[Mg/Fe] stars V distribution with primarily prograde rotation (although

some in retrograde orbits). More bound and closer to the Galactic plane: disk heated origin, by a massive merger able to heat stars at such high z