Black hole to bulge mass correlation in Active Galactic Nuclei: A test for the simple unified formation scheme

TL;DR

This paper investigates the black hole to bulge mass correlation in AGNs, examining how environmental factors influence this relationship and proposing that variations are due to different formation mechanisms and merger-driven accretion.

Contribution

It introduces a unified formation scheme for QSOs and Seyferts, explaining the broad distribution of black hole to bulge mass ratios in AGNs.

Findings

Black hole to bulge mass ratio varies with galaxy environment.

Normal galaxies and bright QSOs represent different limits of black hole evolution.

Different formation mechanisms lead to a broad distribution of mass ratios.

Abstract

A mass correlation of central black holes and their spheroids ~0.002(within a factor of three) is suggested by Hubble Space Telescope (HST) and various ground-based CCD photometries of early type galaxies. The near-IR images of quasar hosts and the emission line measurements of Broad Line Region for bright QSOs present a similar correlation, which supports the speculation of an evolutionary linkage between the early active QSO phase and the central black holes in normal galaxies. On the other hand, recent reverberation mapping of a sample of Seyferts shows a broad distribution of black hole to bulge mass ratio with a mean of ~10^{-3.5}, about one magnitude lower than the value in early type galaxies and bright QSOs. Adopting a simple unified formation scheme for QSOs and Seyferts, we will discuss in this letter the dependence of the black hole to bulge mass ratio in Active Galactic Nuclei (AGNs) on the environmental parameters of the host galaxies. We show a broad distribution of the mass correlation could be due to different velocity dispersion of the accreting gas from different formation mechanism, and the mass ratio in normal galaxies and bright QSOs is probably a limit case of black hole evolution by merger enhanced accretion close to Eddington limit.