Co-Evolution of Supermassive Black Holes and Their Host Galaxies

We study the evolution of the MBH /Mhost relation up to z = 3 for a sample of 96 quasars with known host galaxy luminosities. Black hole masses are estimated assuming virial equilibrium in the broad-line regions, while the host galaxy masses are inferred from their luminosities. With this data, we are able to pin down the evolution of the MBH /Mhost relation over 85% of the age of the universe. While the MBH /Lhost relation remains nearly unchanged, taking into account the aging of the stellar population, we find that the MBH /Mhost ratio (Γ) increases by a factor ∼ 7 from z = 0 to z = 3. We show that the evolution of Γ is independent of radio loudness and quasar luminosity. We propose that the most massive black holes, in their quasar phase at high-redshift, become extremely rare objects in host galaxies of similar mass in the local universe.