  There is strong observational evidence indicating a time lag of order of some
100 Myr between the onset of starburst and AGN activity in galaxies. Dynamical
time lags have been invoked to explain this. We extend this approach by
introducing a viscous time lag the gas additionally needs to flow through the
AGN's accretion disc before it reaches the central black hole. Our calculations
reproduce the observed time lags and are in accordance with the observed
correlation between black hole mass and stellar velocity dispersion.
