The Evolution of M_*/M_BH Between z=2 and z=0

TL;DR

This paper introduces a new method to estimate the ratio of stellar mass to black hole mass across different redshifts, revealing its dependence on black hole mass and significant evolution from z=2 to z=0.

Contribution

The study presents a novel approach combining observational correlations to track M_*/M_BH evolution, emphasizing the importance of black hole mass dependence and host galaxy star formation activity.

Findings

M_*/M_BH depends on black hole mass at all redshifts.

M_*/M_BH increases by a factor of 4-8 from z=2 to z=0.

Evolution is steeper than previous reports when considering only star-forming hosts.

Abstract

We propose a novel method to estimate M_*/M_BH, the ratio of stellar mass (M_*) to black hole mass (M_BH), at various redshifts using two recent observational results: the correlation between the bolometric luminosity of active galactic nuclei (AGN) and the star formation rate (SFR) in their host galaxies, and the correlation between SFR and M_* in star-forming (SF) galaxies. Our analysis is based on M_BH and L_bol measurements in two large samples of type-I AGN at z~1 and z~2, and the measurements of M_*/M_BH in 0.05<z<0.2 red galaxies. We find that M_*/M_BH depends on M_BH at all redshifts. At z~2, M_*/M_BH 280 and ~40 for M_BH=10^8 and M_BH=10^9 M_sol, respectively. M_*/M_BH grows by a factor of ~4-8 from z~2 to z~0 with extreme cases that are as large as 10-20. The evolution is steeper than reported in other studies, probably because we treat only AGN in SF hosts. We caution that estimates of M_*/M_BH evolution which ignore the dependence of this ratio on M_BH can lead to erroneous conclusions.