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Recent work indicates that the nearby Galactic halo is dominated by thedebris from a major accretion event. We confirm that result from an analysis ofAPOGEE-DR14 element abundances and $\textit{Gaia}$-DR2 kinematics of halostars. We show that $\sim$2/3 of nearby halo stars have high orbitaleccentricities ($e \gtrsim 0.8$), and abundance patterns typical of massiveMilky Way dwarf galaxy satellites today, characterised by relatively low[Fe/H], [Mg/Fe], [Al/Fe], and [Ni/Fe]. The trend followed by high $e$ stars inthe [Mg/Fe]-[Fe/H] plane shows a change of slope at [Fe/H]$\sim-1.3$, which isalso typical of stellar populations from relatively massive dwarf galaxies. Low$e$ stars exhibit no such change of slope within the observed [Fe/H] range andshow slightly higher abundances of Mg, Al and Ni. Unlike their low $e$counterparts, high $e$ stars show slightly retrograde motion, make highervertical excursions and reach larger apocentre radii. By comparing the positionin [Mg/Fe]-[Fe/H] space of high $e$ stars with those of accreted galaxies fromthe EAGLE suite of cosmological simulations we constrain the mass of theaccreted satellite to be in the range $10^{8.5}\lesssim M_*\lesssim10^{9}\mathrm{M_\odot}$. We show that the median orbital eccentricities ofdebris are largely unchanged since merger time, implying that this accretionevent likely happened at $z\lesssim1.5$. The exact nature of the low $e$population is unclear, but we hypothesise that it is a combination of$\textit{in situ}$ star formation, high $|z|$ disc stars, lower mass accretionevents, and contamination by the low $e$ tail of the high $e$ population.Finally, our results imply that the accretion history of the Milky Way wasquite unusual.

The origin of accreted stellar halo populations in the Milky Way using APOGEE, $\textit{Gaia}$, and the EAGLE simulations