TY - JOUR
T1 - Timing the early assembly of the milky way with the H3 survey
AU - Bonaca, Ana
AU - Conroy, Charlie
AU - Cargile, Phillip A.
AU - Naidu, Rohan P.
AU - Johnson, Benjamin D.
AU - Zaritsky, Dennis
AU - Ting, Yuan Sen
AU - Caldwell, Nelson
AU - Han, Jiwon Jesse
AU - van Dokkum, Pieter
N1 - Publisher Copyright:
Copyright © 2020, The Authors. All rights reserved.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/4/23
Y1 - 2020/4/23
N2 - The archaeological record of stars in the Milky Way opens a uniquely detailed window into the early formation and assembly of galaxies. Here we use 11,000 main-sequence turn-off stars with well-measured ages, [Fe/H], [α/Fe], and orbits from the H3 Survey and Gaia to time the major events in the early Galaxy. Located beyond the Galactic plane, 1 ≲ |Z|/kpc ≲ 4, this sample contains three chemically distinct groups: a low metallicity population, and low-α and high-α groups at higher metallicity. The age and orbit distributions of these populations show that: 1) the high-α group, which includes both disk stars and the in-situ halo, has a star-formation history independent of eccentricity that abruptly truncated 8.3±0.1 Gyr ago (z ≃ 1); 2) the low metallicity population, which we identify as the accreted stellar halo, is on eccentric orbits and its star formation truncated 10.2.+0−0..21 Gyr ago (z ≃ 2); 3) the low-α population is primarily on low eccentricity orbits and the bulk of its stars formed less than 8 Gyr ago. These results suggest a scenario in which the Milky Way accreted a satellite galaxy at z ≈ 2 that merged with the early disk by z ≈ 1. This merger truncated star formation in the early high-α disk and perturbed a fraction of that disk onto halo-like orbits. The merger enabled the formation of a chemically distinct, low-α disk at z ≲ 1. The lack of any stars on halo-like orbits at younger ages indicates that this event was the last significant disturbance to the Milky Way disk.
AB - The archaeological record of stars in the Milky Way opens a uniquely detailed window into the early formation and assembly of galaxies. Here we use 11,000 main-sequence turn-off stars with well-measured ages, [Fe/H], [α/Fe], and orbits from the H3 Survey and Gaia to time the major events in the early Galaxy. Located beyond the Galactic plane, 1 ≲ |Z|/kpc ≲ 4, this sample contains three chemically distinct groups: a low metallicity population, and low-α and high-α groups at higher metallicity. The age and orbit distributions of these populations show that: 1) the high-α group, which includes both disk stars and the in-situ halo, has a star-formation history independent of eccentricity that abruptly truncated 8.3±0.1 Gyr ago (z ≃ 1); 2) the low metallicity population, which we identify as the accreted stellar halo, is on eccentric orbits and its star formation truncated 10.2.+0−0..21 Gyr ago (z ≃ 2); 3) the low-α population is primarily on low eccentricity orbits and the bulk of its stars formed less than 8 Gyr ago. These results suggest a scenario in which the Milky Way accreted a satellite galaxy at z ≈ 2 that merged with the early disk by z ≈ 1. This merger truncated star formation in the early high-α disk and perturbed a fraction of that disk onto halo-like orbits. The merger enabled the formation of a chemically distinct, low-α disk at z ≲ 1. The lack of any stars on halo-like orbits at younger ages indicates that this event was the last significant disturbance to the Milky Way disk.
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M3 - Article
AN - SCOPUS:85094438684
JO - Nuclear Physics A
JF - Nuclear Physics A
SN - 0375-9474
ER -