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In the Milky Way, recent progress in the exploration of its assembly historyis driven by the tremendous amount of high-quality data delivered by Gaia,which has revealed a number of substructures potentially linked to severalancient accretion events. In this work, aiming to explore the phase-spacestructure of accreted stars, we analyze six M31/MW analogues from the HESTIAsuite of cosmological hydrodynamics zoom-in simulations of the Local Group. Wefound that all the HESTIA galaxies experience a few dozen mergers but only 1-4mergers have the stellar mass ratio >0.2 where, depending on the halodefinition, the most massive merger contributes from 20% to 70% of the totalstellar halo. Individual merger remnants show diverse density distributions atz=0, significantly overlapping with each other and with the in-situ stars inthe ELz, UV and RVphi coordinates. The mergers debris often change theirposition in the ELz with time due to the galactic mass growth and thenon-axisymmetry of the potential. In agreement with previous works, we showthat even individual merger debris exhibit a number of distinct ELz features.In the UV plane, all HESTIA galaxies reveal radially hot, non-rotating orweakly counter-rotating, Gaia-Sausage-like features. We found an age gradientin Elz space for the individual debris, where the youngest stars, formed in theinner regions of accreting systems, deposit to the innermost regions of thehost. The bulk of these stars is being formed during the last stages ofaccretion, making it possible to date the merger. In actions space (Jr, Jz,J\phi), the mergers debris do not appear as isolated substructures but areinstead scattered over a large parameters area and overlapping with the in-situstars. We also introduce a purely kinematic space (Jz/Jr-eccentricity), wheredifferent merger debris can be disentangled better from each other and from thein-situ stars.

The stellar halo in Local Group Hestia simulations II. The accreted component