The distribution of [α/Fe] in the Milky Way disc

Fiorenzo Vincenzo, David H. Weinberg, Andrea Miglio, Richard R. Lane, Alexandre Roman-Lopes

Research output: Contribution to journalArticlepeer-review

18 Downloads (Pure)

Abstract

Using a sample of red giant stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16, we infer the conditional distribution p([α/Fe] | [Fe/H]) in the Milky Way disk for the α-elements Mg, O, Si, S, and Ca. In each bin of [Fe/H] and Galactocentric radius R, we model p([α/Fe]) as a sum of two Gaussians, representing ‘low-α’ and ‘high-α’ populations with scale heights z1 = 0.45 kpc and z2 = 0.95 kpc, respectively. By accounting for age-dependent and z-dependent selection effects in APOGEE, we infer the [α/Fe] distributions that would be found for a fair sample of long-lived stars covering all z. Near the Solar circle, this distribution is bimodal at sub-solar [Fe/H], with the low-α and high-α peaks clearly separated by a minimum at intermediate [α/Fe]. In agreement with previous results, we find that the high-α population is more prominent at smaller R, lower [Fe/H], and larger |z|, and that the sequence separation is smaller for Si and Ca than for Mg, O, and S. We find significant intrinsic scatter in [α/Fe] at fixed [Fe/H] for both the low-α and high-α populations, typically ∼0.04-dex. The means, dispersions, and relative amplitudes of this two-Gaussian description, and the dependence of these parameters on R, [Fe/H], and α-element, provide a quantitative target for chemical evolution models and a test for hydrodynamic simulations of disk galaxy formation. We argue that explaining the observed bimodality will probably require one or more sharp transitions in the disk’s gas accretion, star formation, or outflow history in addition to radial mixing of stellar populations.
Original languageEnglish
Pages (from-to)5903-5920
JournalMonthly Notices of the Royal Astronomical Society
Volume508
Issue number4
Early online date7 Oct 2021
DOIs
Publication statusPublished - Dec 2021

Keywords

  • astro-ph.GA
  • astro-ph.SR
  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint

Dive into the research topics of 'The distribution of [α/Fe] in the Milky Way disc'. Together they form a unique fingerprint.

Cite this