The building blocks of the Milky Way halo using APOGEE and Gaia or Is the Galaxy a typical galaxy?

We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized by a chemical composition resembling those of low-mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:in situ ratio within our metal-poor ([Fe/H] < –0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.

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Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Horta

Schiavon

Mackereth

et al. 2020

Monthly Notices of the Royal Astronomical Society

173

218

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Lithium abundances as a tracer of asymptotic giant branch star pollution in the globular cluster NGC 6752

Lucatello

Rain

et al. 2022

Monthly Notices of the Royal Astronomical Society

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This paper presents a chemical abundance analysis of 217 stars in the metal-poor globular cluster NGC 6752, distributed from the turn-off to the lower red giant branch. Al and Li abundances were derived through spectral synthesis applied to spectra collected with FLAMES, in both GIRAFFE and UVES modes. The work aims to gain insight into the nature of the polluter(s) responsible for the abundance variations and the C-N, Na-O, Al-Mg anticorrelations associated with the multiple-population phenomenon. We found a plateau at A(Li) = 2.33 ± 0.06 dex in unevolved stars, with the average Li content decreasing continuously down to ∼1.25 dex at the bottom of the red giant branch. As expected in the classic anticorrelation scenario, we found stars low in Al and high in Li abundance, and stars high in Al and low in Li. However, in addition, we also found evidence of Al-rich, second-generation stars with high Li content. This finding suggests the need for Li production, known to happen in intermediate-mass (∼4–8 M⊙) asymptotic giant branch stars through the Cameron–Fowler mechanism. It is worth noting that the Li abundance observed in Al-rich stars never exceeds that in Al-poor stars.

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An enquiry on the origins of N-rich stars in the inner Galaxy based on APOGEE chemical compositions

Kisku

Schiavon

Horta

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Recent evidence based on APOGEE data for stars within a few kpc of the Galactic centre suggests that dissolved globular clusters (GCs) contribute significantly to the stellar mass budget of the inner halo. In this paper we enquire into the origins of tracers of GC dissolution, N-rich stars, that are located in the inner 4 kpc of the Milky Way. From an analysis of the chemical compositions of these stars we establish that about 30% of the N-rich stars previously identified in the inner Galaxy may have an accreted origin. This result is confirmed by an analysis of the kinematic properties of our sample. The specific frequency of N-rich stars is quite large in the accreted population, exceeding that of its in situ counterparts by near an order of magnitude, in disagreement with predictions from numerical simulations. We hope that our numbers provide a useful test to models of GC formation and destruction.

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The building blocks of the Milky Way halo using APOGEE and Gaia or Is the Galaxy a typical galaxy?

Cited by 4 publications

References 27 publications

Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Lithium abundances as a tracer of asymptotic giant branch star pollution in the globular cluster NGC 6752

An enquiry on the origins of N-rich stars in the inner Galaxy based on APOGEE chemical compositions

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