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arXiv · 1809.02368

The assembly history of the Galactic inner halo inferred from alpha-patterns

Emma Fernández-Alvar·Patricia B. Tissera·Leticia Carigi·William J. Schuster·Timothy C. Beers·Vasily A. Belokurov
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Abstract

We explore the origin of the observed decline in [O/Fe] (and [Mg/Fe]) with Galactocentric distance for high-metallicity stars ([Fe/H] > -1.1), based on a sample of halo stars selected within the Apache Point Observatory Galactic Evolution Experiment (APOGEE) fourteenth data release (DR14). We also analyse the characteristics of the [$α$/Fe] distributions in the inner-halo regions inferred from two zoom-in Milky Way mass-sized galaxies that are taken as case studies. One of them qualitatively reproduces the observed trend to have higher fraction of $α$-rich star for decreasing galactocentric distance; the other exhibits the opposite trend. We find that stars with [Fe/H] > -1.1 located in the range [15 - 30] kpc are consistent with formation in two starbursts, with maxima separated by about ~ 1 Gyr. We explore the contributions of stellar populations with different origin to the [$α$/Fe] gradients detected in stars with [Fe/H] > -1.1. Our analysis reveals that the simulated halo that best matches the observed chemical trends is characterised by an accretion history involving low to intermediate-mass satellite galaxies with a short and intense burst of star formation, and contributions from a more massive satellite with dynamical masses about ~ 10$^{10}$M$_{\odot}$, distributing low-[$α$/Fe] stars at intermediate radius.

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Emma Fernández-Alvar, Patricia B. Tissera, Leticia Carigi, William J. Schuster, Timothy C. Beers, Vasily A. Belokurov. 2019-02-12. The assembly history of the Galactic inner halo inferred from alpha-patterns. https://doi.org/10.1093/mnras%2Fstz443

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