TY - JOUR
T1 - The origin of accreted stellar halo populations in the Milky Way using APOGEE, Gaia, and the EAGLE simulations
AU - Mackereth, J. Ted
AU - Schiavon, Ricardo P.
AU - Pfeffer, Joel
AU - Hayes, Christian R.
AU - Bovy, Jo
AU - Anguiano, Borja
AU - Allende Prieto, Carlos
AU - Hasselquist, Sten
AU - Holtzman, Jon
AU - Johnson, Jennifer A.
AU - Majewski, Steven R.
AU - O'Connell, Robert
AU - Shetrone, Matthew
AU - Tissera, Patricia B.
AU - Fernández-Trincado, J. G.
PY - 2019/1/21
Y1 - 2019/1/21
N2 - Recent work indicates that the nearby Galactic halo is dominated by the debris from a major accretion event. We confirm that result from an analysis of APOGEE-DR14 element abundances and Gaia-DR2 kinematics of halo stars. We show that ̃2/3 of nearby halo stars have high orbital eccentricities (e ≳ 0.8), and abundance patterns typical of massive Milky Way dwarf galaxy satellites today, characterized by relatively low [Fe/H], [Mg/Fe], [Al/Fe], and [Ni/Fe]. The trend followed by high-e stars in the [Mg/Fe]-[Fe/H] plane shows a change of slope at [Fe/H] ̃ -1.3, which is also typical of stellar populations from relatively massive dwarf galaxies. Low-e stars exhibit no such change of slope within the observed [Fe/H] range and show slightly higher abundances of Mg, Al, and Ni. Unlike their low-e counterparts, high-e stars show slightly retrograde motion, make higher vertical excursions, and reach larger apocentre radii. By comparing the position in [Mg/Fe]-[Fe/H] space of high-e stars with those of accreted galaxies from the EAGLE suite of cosmological simulations, we constrain the mass of the accreted satellite to be in the range 108.5 ≲ M* ≲ 109 M☉. We show that the median orbital eccentricities of debris are largely unchanged since merger time, implying that this accretion event likely happened at z ≲ 1.5. The exact nature of the low-e population is unclear, but we hypothesize that it is a combination of in situ star formation, high-|z| disc stars, lower mass accretion events, and contamination by the low-e tail of the high-e population. Finally, our results imply that the accretion history of the Milky Way was quite unusual....
AB - Recent work indicates that the nearby Galactic halo is dominated by the debris from a major accretion event. We confirm that result from an analysis of APOGEE-DR14 element abundances and Gaia-DR2 kinematics of halo stars. We show that ̃2/3 of nearby halo stars have high orbital eccentricities (e ≳ 0.8), and abundance patterns typical of massive Milky Way dwarf galaxy satellites today, characterized by relatively low [Fe/H], [Mg/Fe], [Al/Fe], and [Ni/Fe]. The trend followed by high-e stars in the [Mg/Fe]-[Fe/H] plane shows a change of slope at [Fe/H] ̃ -1.3, which is also typical of stellar populations from relatively massive dwarf galaxies. Low-e stars exhibit no such change of slope within the observed [Fe/H] range and show slightly higher abundances of Mg, Al, and Ni. Unlike their low-e counterparts, high-e stars show slightly retrograde motion, make higher vertical excursions, and reach larger apocentre radii. By comparing the position in [Mg/Fe]-[Fe/H] space of high-e stars with those of accreted galaxies from the EAGLE suite of cosmological simulations, we constrain the mass of the accreted satellite to be in the range 108.5 ≲ M* ≲ 109 M☉. We show that the median orbital eccentricities of debris are largely unchanged since merger time, implying that this accretion event likely happened at z ≲ 1.5. The exact nature of the low-e population is unclear, but we hypothesize that it is a combination of in situ star formation, high-|z| disc stars, lower mass accretion events, and contamination by the low-e tail of the high-e population. Finally, our results imply that the accretion history of the Milky Way was quite unusual....
UR - http://www.scopus.com/inward/record.url?scp=85060171653&partnerID=8YFLogxK
U2 - 10.1093/mnras/sty2955
DO - 10.1093/mnras/sty2955
M3 - Article
SN - 0035-8711
VL - 482
SP - 3426
EP - 3442
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -