The quasar M_bh - M_host relation through Cosmic Time II - Evidence for evolution from z=3 to the present age

TL;DR

This study investigates the evolution of the black hole mass to host galaxy mass relation in quasars from redshift 0 to 3, revealing a significant increase in the ratio over cosmic time.

Contribution

It provides the first comprehensive analysis of the M_bh - M_host relation evolution up to z=3, accounting for stellar aging effects and showing a substantial increase in the ratio.

Findings

The M_bh - L_host relation remains nearly unchanged up to z=3.

The M_bh / M_host ratio increases by a factor of ~7 from z=0 to z=3.

The evolution of the ratio is independent of radio loudness and quasar luminosity.

Abstract

We study the dependence of the M_bh - M_host relation on the redshift up to z=3 for a sample of 96 quasars the host galaxy luminosities of which are known. Black hole masses were estimated assuming virial equilibrium in the broad line regions (Paper I), while the host galaxy masses were inferred from their luminosities. With this data we are able to pin down the redshift dependence of the M_bh - M_host relation along 85 per cent of the Universe age. We show that, in the sampled redshift range, the M_bh - L_host relation remains nearly unchanged. Once we take into account the aging of the stellar population, we find that the M_bh / M_host ratio (Gamma) increases by a factor ~7 from z=0 to z=3. We show that Gamma evolves with z regardless of the radio loudness and of the quasar luminosity. We propose that most massive black holes, living their quasar phase at high-redshift, become extremely rare objects in host galaxies of similar mass in the Local Universe.