The assembly history of the Galactic inner halo inferred from α-element patterns
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 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2019
- DOI:
- 10.1093/mnras/stz443
- arXiv:
- arXiv:1809.02368
- Bibcode:
- 2019MNRAS.485.1745F
- Keywords:
-
- methods: numerical;
- techniques: spectroscopic;
- Galaxy: abundances;
- Galaxy: formation;
- Galaxy: halo;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, 8 figures. Accepted for publication in MNRAS