Examinando por Autor "Fernandez-Alvar, Emma"

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    The assembly history of the Galactic inner halo inferred from α-element patterns
    (Monthly Notices of the Royal Astronomical Society, 2019-02-15) Fernandez-Alvar, Emma; Tissera, Patricia B.; Carigi, Leticia; Schuster, William J.; Beers, Timothy C.; Belokurov, Vasily A.
    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 characterized 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 ∼1010 M, distributing low [α/Fe] stars at intermediate radius.