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(Reduced) Using the recent cosmological high-resolution zoom-in simulations,NewHorizon and Galactica, in which the evolution of black hole spin is followedon the fly, we have tracked the cosmic history of a hundred of black holes(BHs) with a mass greater than 2x10^4 Ms. For each of them, we have studied thevariations of the three dimensional angle (Psi) subtended between the BH spinsand the angular momentum vectors of their host galaxies. The analysis of theindividual evolution of the most massive BHs suggests that they are generallypassing by three different regimes. First, for a short period after theirbirth, low mass BHs (<3x10^4 Ms) are rapidly spun up by gas accretion and theirspin tends to be aligned with their host galaxy spin. Then follows a secondphase in which the accretion of gas onto low mass BHs (<10^5 Ms) is quitechaotic and inefficient, reflecting the complex and disturbed morphologies offorming proto-galaxies at high redshifts. The variations of Psi are rathererratic during this phase and are mainly driven by the rapid changes of thedirection of the galaxy angular momentum. Then, in a third and long phase, BHsare generally well settled in the center of galaxies around which the gasaccretion becomes much more coherent (>10^5 Ms). In this case, the BH spinstend to be well aligned with the angular momentum of their host galaxy and thisconfiguration is generally stable even though BH merger episodes can temporallyinduce misalignment. We have also derived the distributions of cos(Psi) atdifferent redshifts and found that BHs and galaxy spins are generally aligned.Finally, based on a Monte Carlo method, we also predict statistics for the 2-dprojected spin-orbit angles lambda. In particular, the distribution of lambdatraces well the alignment tendency in the 3-d analysis. Such predictionsprovide an interesting background for future observational analyses.

Cosmic evolution of black hole-spin and galaxy orientations: clues from the NewHorizon and Galactica simulations