We present a new suite of hydrodynamical simulations and use it to study , in detail , black hole and galaxy properties .
The high time , spatial and mass resolution , and realistic orbits and mass ratios , down to 1:6 and 1:10 , enable us to meaningfully compare star formation rate ( SFR ) and BH accretion rate ( BHAR ) timescales , temporal behaviour and relative magnitude .
We find that ( i ) BHAR and galaxy-wide SFR are typically temporally uncorrelated , and have different variability timescales , except during the merger proper , lasting \sim 0.2 - 0.3 Gyr .
BHAR and nuclear ( < 100 pc ) SFR are better correlated , and their variability are similar .
Averaging over time , the merger phase leads typically to an increase by a factor of a few in the BHAR/SFR ratio .
( ii ) BHAR and nuclear SFR are intrinsically proportional , but the correlation lessens if the long-term SFR is measured .
( iii ) Galaxies in the remnant phase are the ones most likely to be selected as systems dominated by an active galactic nucleus ( AGN ) , because of the long time spent in this phase .
( iv ) The timescale over which a given diagnostic probes the SFR has a profound impact on the recovered correlations with BHAR , and on the interpretation of observational data .