Age Determination of Galaxy Merger Remnant Stars using Asteroseismology

Camilla Borre; Victor Aguirre Børsen-Koch; Amina Helmi; Helmer Koppelman; Martin B. Nielsen; Jakob Rørsted Mosumgaard; Dennis Stello; Amalie Stokholm; Mark Lykke Winther; Guy R. Davies; Marc Hon; Diederik Kruijssen; Chervin Laporte; Claudia Reyes; Jie Yu

doi:10.1093/mnras/stac1498

Age Determination of Galaxy Merger Remnant Stars using Asteroseismology

Camilla Borre, Victor Aguirre Børsen-Koch, Amina Helmi, Helmer Koppelman, Martin B. Nielsen, Jakob Rørsted Mosumgaard, Dennis Stello, Amalie Stokholm, Mark Lykke Winther, Guy R. Davies, Marc Hon, Diederik Kruijssen, Chervin Laporte, Claudia Reyes, Jie Yu

Institut for Fysik og Astronomi

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avis › Tidsskriftartikel › Forskning › peer review

Abstract

The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2, we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy's history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8-10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.

Originalsprog	Engelsk
Tidsskrift	Monthly Notices of the Royal Astronomical Society
Vol/bind	514
Nummer	2
Sider (fra-til)	2527–2544
Antal sider	18
ISSN	0035-8711
DOI	https://doi.org/10.1093/mnras/stac1498
Status	Udgivet - aug. 2022

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10.1093/mnras/stac1498

https://arxiv.org/pdf/2111.01669.pdf

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Borre, C., Børsen-Koch, V. A., Helmi, A., Koppelman, H., Nielsen, M. B., Mosumgaard, J. R., Stello, D., Stokholm, A., Winther, M. L., Davies, G. R., Hon, M., Kruijssen, D., Laporte, C., Reyes, C., & Yu, J. (2022). Age Determination of Galaxy Merger Remnant Stars using Asteroseismology. Monthly Notices of the Royal Astronomical Society, 514(2), 2527–2544. https://doi.org/10.1093/mnras/stac1498

@article{c336b218062f416799664dfb8aae1ec4,

title = "Age Determination of Galaxy Merger Remnant Stars using Asteroseismology",

abstract = "The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2, we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy's history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8-10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.",

keywords = "Asteroseismology, Galaxy: evolution, Stars: abundances, Stars: kinematics and dynamics",

author = "Camilla Borre and B{\o}rsen-Koch, {Victor Aguirre} and Amina Helmi and Helmer Koppelman and Nielsen, {Martin B.} and Mosumgaard, {Jakob R{\o}rsted} and Dennis Stello and Amalie Stokholm and Winther, {Mark Lykke} and Davies, {Guy R.} and Marc Hon and Diederik Kruijssen and Chervin Laporte and Claudia Reyes and Jie Yu",

year = "2022",

month = aug,

doi = "10.1093/mnras/stac1498",

language = "English",

volume = "514",

pages = "2527–2544",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "Oxford University Press",

number = "2",

}

Borre, C, Børsen-Koch, VA, Helmi, A, Koppelman, H, Nielsen, MB, Mosumgaard, JR , Stello, D , Stokholm, A , Winther, ML, Davies, GR, Hon, M, Kruijssen, D, Laporte, C, Reyes, C & Yu, J 2022, 'Age Determination of Galaxy Merger Remnant Stars using Asteroseismology', Monthly Notices of the Royal Astronomical Society, bind 514, nr. 2, s. 2527–2544. https://doi.org/10.1093/mnras/stac1498

TY - JOUR

T1 - Age Determination of Galaxy Merger Remnant Stars using Asteroseismology

AU - Borre, Camilla

AU - Børsen-Koch, Victor Aguirre

AU - Helmi, Amina

AU - Koppelman, Helmer

AU - Nielsen, Martin B.

AU - Mosumgaard, Jakob Rørsted

AU - Stello, Dennis

AU - Stokholm, Amalie

AU - Winther, Mark Lykke

AU - Davies, Guy R.

AU - Hon, Marc

AU - Kruijssen, Diederik

AU - Laporte, Chervin

AU - Reyes, Claudia

AU - Yu, Jie

PY - 2022/8

Y1 - 2022/8

N2 - The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2, we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy's history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8-10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.

AB - The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2, we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy's history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8-10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.

KW - Asteroseismology

KW - Galaxy: evolution

KW - Stars: abundances

KW - Stars: kinematics and dynamics

UR - http://www.scopus.com/inward/record.url?scp=85133672092&partnerID=8YFLogxK

U2 - 10.1093/mnras/stac1498

DO - 10.1093/mnras/stac1498

M3 - Journal article

SN - 0035-8711

VL - 514

SP - 2527

EP - 2544

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 2

ER -

Age Determination of Galaxy Merger Remnant Stars using Asteroseismology

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