Probing the Growth of Massive Black Holes with Black Hole-Host Galaxy Spin Correlations

TL;DR

This paper investigates how different growth channels of supermassive black holes influence their spins and proposes using spin magnitude and orientation correlations with host galaxies to distinguish their formation histories.

Contribution

It introduces a method to differentiate black hole growth channels by analyzing spin magnitudes and directions via gravitational wave observations and galaxy correlations.

Findings

Different growth channels produce distinguishable spin magnitudes.

Spin direction correlation with host galaxies can constrain formation scenarios.

Proposes using LISA observations to identify black hole growth pathways.

Abstract

Supermassive black holes (SMBHs) are commonly found at the centers of their host galaxies, but their formation still remains an open question. In light of the tight correlation between the BH mass and the velocity dispersions of the bulge component of the host galaxy, a BH-host galaxy coevolution scenario has been established. Such description however still contains many theoretical uncertainties, including the puzzels about the formation of BH seeds at high redshifts and the growth channel fueling these seeds. In this work, we systematically analyze the signatures of different growth channels on MBH spins. We show that different growth channels can be partially distinguished with the magnitudes of MBH spins infered from extreme-mass-ratio-inspirals detected by the Laser Interferometer Space Antenna. In addition, we propose to measure the correlation between the directions of MBH spins and their host galaxy spins, which is possible for extreme mass-ratio inspirals happening in low-redshift galaxies ($z \le 0.3$). With the inclusion of spin direction correlation different formation channels shall be significantly better constrained.