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Selecting accreted populations : Metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations

Feuillet, Diane K. LU orcid ; Sahlholdt, Christian L. LU ; Feltzing, Sofia LU orcid and Casagrande, Luca (2021) In Monthly Notices of the Royal Astronomical Society 508(1). p.1489-1508
Abstract

Identifying stars found in the Milky Way as having formed in situ or accreted can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus (GSE) and Sequoia accretion events. These samples are used to characterize the GSE and Sequoia population metallicity distribution functions, elemental abundance patterns, age distributions, and progenitor masses. We find that the GSE population has a mean [Fe/H] ∼-1.15 and a mean age of 10-12 Gyr. GSE has a single sequence in [Mg/Fe] versus [Fe/H] consistent with the onset of SN Ia Fe contributions and uniformly low [Al/Fe] of ∼-0.25 dex. The derived properties of the Sequoia population are strongly... (More)

Identifying stars found in the Milky Way as having formed in situ or accreted can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus (GSE) and Sequoia accretion events. These samples are used to characterize the GSE and Sequoia population metallicity distribution functions, elemental abundance patterns, age distributions, and progenitor masses. We find that the GSE population has a mean [Fe/H] ∼-1.15 and a mean age of 10-12 Gyr. GSE has a single sequence in [Mg/Fe] versus [Fe/H] consistent with the onset of SN Ia Fe contributions and uniformly low [Al/Fe] of ∼-0.25 dex. The derived properties of the Sequoia population are strongly dependent on the kinematic selection. We argue the selection with the least contamination is Jφ/Jtot < -0.6 and (Jz - JR)/Jtot < 0.1. This results in a mean [Fe/H] ∼-1.3 and a mean age of 12-14 Gyr. The Sequoia population has a complex elemental abundance distribution with mainly high-[Mg/Fe] stars. We use the GSE [Al/Fe] versus [Mg/H] abundance distribution to inform a chemically based selection of accreted stars, which is used to remove possible contaminant stars from the GSE and Sequoia samples.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: abundances, Galaxy: formation, Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: stellar content
in
Monthly Notices of the Royal Astronomical Society
volume
508
issue
1
pages
20 pages
publisher
Oxford University Press
external identifiers
  • scopus:85118182461
ISSN
0035-8711
DOI
10.1093/mnras/stab2614
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
id
07af36cb-26d6-4892-a4c8-58f7fb6dc8c2
date added to LUP
2021-11-13 09:24:15
date last changed
2024-04-20 16:16:13
@article{07af36cb-26d6-4892-a4c8-58f7fb6dc8c2,
  abstract     = {{<p>Identifying stars found in the Milky Way as having formed in situ or accreted can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus (GSE) and Sequoia accretion events. These samples are used to characterize the GSE and Sequoia population metallicity distribution functions, elemental abundance patterns, age distributions, and progenitor masses. We find that the GSE population has a mean [Fe/H] ∼-1.15 and a mean age of 10-12 Gyr. GSE has a single sequence in [Mg/Fe] versus [Fe/H] consistent with the onset of SN Ia Fe contributions and uniformly low [Al/Fe] of ∼-0.25 dex. The derived properties of the Sequoia population are strongly dependent on the kinematic selection. We argue the selection with the least contamination is Jφ/Jtot &lt; -0.6 and (Jz - JR)/Jtot &lt; 0.1. This results in a mean [Fe/H] ∼-1.3 and a mean age of 12-14 Gyr. The Sequoia population has a complex elemental abundance distribution with mainly high-[Mg/Fe] stars. We use the GSE [Al/Fe] versus [Mg/H] abundance distribution to inform a chemically based selection of accreted stars, which is used to remove possible contaminant stars from the GSE and Sequoia samples.</p>}},
  author       = {{Feuillet, Diane K. and Sahlholdt, Christian L. and Feltzing, Sofia and Casagrande, Luca}},
  issn         = {{0035-8711}},
  keywords     = {{Galaxy: abundances; Galaxy: formation; Galaxy: halo; Galaxy: kinematics and dynamics; Galaxy: stellar content}},
  language     = {{eng}},
  month        = {{11}},
  number       = {{1}},
  pages        = {{1489--1508}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{Selecting accreted populations : Metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations}},
  url          = {{http://dx.doi.org/10.1093/mnras/stab2614}},
  doi          = {{10.1093/mnras/stab2614}},
  volume       = {{508}},
  year         = {{2021}},
}