The Relative Growth of Black Holes and of the Stellar Components of Galaxies

TL;DR

This study uses a semi-analytic galaxy formation model to analyze how different stellar components of galaxies correlate with supermassive black hole masses, revealing tight bulge correlations but large scatter with discs and pseudo-bulges.

Contribution

It provides a detailed comparison of galaxy stellar components and SMBH growth within a cosmological model, highlighting the differing correlations and their physical origins.

Findings

Bulge mass correlates tightly with SMBH mass.

Disc mass shows large scatter in SMBH correlation.

Pseudo-bulge mass has little to no correlation with SMBH mass.

Abstract

Recent observations indicate that the mass of Supermassive Black Holes (SMBHs) correlate differently with different galaxy stellar components. Comparing such observations with the results of "ab initio" galaxy formation models can provide insight on the mechanisms leading to the growth of SMBHs. Here we use a state-of-the-art semi-analytic model of galaxy formation to investigate the correlation of the different galaxy stellar components with the mass of the central SMBH. The stellar mass in the disc, in the bulge, and in the pseudo-bulge of galaxies is related to quiescent star formation, to galaxy interactions, and to the loss of angular momentum following disc instabilities, respectively. Consistently with recent findings, we find that while the predicted bulge masses are tightly correlated with the SMBH masses, the correlation between the latter and the galactic discs shows a much larger scatter, in particular when bulgeless galaxies are considered. In addition, we obtain that the predicted masses of pseudo-bulges shows little or no-correlation with the masses of SMBHs. We track the histories of merging, star formation, and SMBH accretion to investigate the physical processes at the origin of such findings within the context of cosmological models of galaxy formation. Finally, we discuss the effects of variations of our assumed fiducial model on the results.