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Title: Chemical enrichment and radial migration in the Galactic disc – the origin of the [αFe] double sequence

Journal Article · · Monthly Notices of the Royal Astronomical Society
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Sydney, NSW (Australia); ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D) (Australia)
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The ([α/Fe], [Fe/H]) distribution of Milky Way stars shows at least two distinct sequences, which have traditionally been associated with the thin and thick disc components. The abundance distribution varies systematically with location R and |z| across the Galaxy. We reproduce this using an analytical chemodynamical model that includes the effects of radial migration and kinematic heating. Unlike some earlier models, our scheme does not require a distinct thick disc component emerging from a separate evolutionary path. The proposed model has a continuous star formation history and a continuous age velocity dispersion relation. Moreover, [α/Fe] is constant for stellar ages less than 8 Gyr, but increases sharply for older stars over a time-scale of 1.5 Gyr. The gap between the two sequences is due to this sharp transition. We show that the high-[α/Fe] sequence at the low-metallicity end is simply a pile-up of old stars, but towards the high-metallicity end, the age progressively decreases and stars have small birth radii. Our model successfully explains the uniformity of the locus of the high-[α/Fe] sequence across different locations. The low-[α/Fe] sequence contains stars with different birth radii that owes its existence to radial migration. For the low-[α/Fe] stars, angular momentum is anticorrelated with [Fe/H], while the opposite is true for high-[α/Fe] stars. We show that the later trend can be explained by the increase of circular velocity with time. If radial migration is not included, the model fails to generate the double sequence and instead shows only a single sequence. Our simple scheme has major advantages over earlier chemodynamical models, as we show.

Research Organization:
US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
Sponsoring Organization:
USDOE Office of Science (SC); Australian Research Council (ARC)
Contributing Organization:
Sloan Digital Sky Survey (SDSS)
OSTI ID:
1982511
Journal Information:
Monthly Notices of the Royal Astronomical Society, Vol. 507, Issue 4; ISSN 0035-8711
Publisher:
Oxford University PressCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Galaxy abundances
galaxy disc
galaxy evolution
galaxy formation
galaxy structure