Lifetimes of active Black Holes

• The standard definition of QSO lifetime is meaningful only if QSOs are on-off switches (i.e. when a constant eddington ratio is assumed for all sources at every redshift).

• Here a broad accretion rate distribution is not only allowed, but calculated self-consitently: a different definition of lifetime should be introduced

• We can define the partial accretion weighted mean lifetime for objects of mass (today) M0, in the redshift interval Dz