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We explore the evolution of the different ejecta components generated duringthe merger of a neutron star (NS) and a black hole (BH). Our focus is theinterplay between material ejected dynamically during the merger, and the windlaunched on a viscous timescale by the remnant accretion disk. These componentsare expected to contribute to an electromagnetic transient and to producer-process elements, each with a different signature when considered separately.Here we introduce a two-step approach to investigate their combined evolution,using two- and three-dimensional hydrodynamic simulations. Starting from theoutput of a merger simulation, we identify each component in the initialcondition based on its phase space distribution, and evolve the accretion diskin axisymmetry. The wind blown from this disk is injected into athree-dimensional computational domain where the dynamical ejecta is evolved.We find that the wind can suppress fallback accretion on timescales longer than~100 ms. Due to self-similar viscous evolution, the disk accretion at latetimes nevertheless approaches a power-law time dependence $\propto t^{-2.2}$.This can power some late-time GRB engine activity, although the availableenergy is significantly less than in traditional fallback models. Inclusion ofradioactive heating due to the r-process does not significantly affect thefallback accretion rate or the disk wind. We do not find any significantmodification to the wind properties at large radius due to interaction with thedynamical ejecta. This is a consequence of the different expansion velocitiesof the two components.

The interplay of disk wind and dynamical ejecta in the aftermath of neutron star - black hole mergers