Co-evolution of black holes and galaxies: the role of selection biases

Quasars are tracers of the cosmological evolution of the Black Hole mass- host galaxy relation, and indicate that the formation of BHanticipated that of the host galaxies. We find that selection effects andstatistical biases dominate the interpretation of the observational results;and co-evolution (= constant BH/galaxy mass ratio) is still compatiblewith observations.