Galactic merger implications for eccentric nuclear disks: a mechanism for disk alignment

TL;DR

This study investigates how galactic mergers, especially the presence of a secondary SMBH, influence the stability and alignment of eccentric nuclear disks, revealing a mechanism for disk stabilization and implications for M31.

Contribution

First simulation-based analysis of eccentric nuclear disk dynamics under galaxy mergers, showing SMBH interactions can stabilize and align the disk.

Findings

A second SMBH disrupts the disk; distant SMBHs can stabilize and align it.

Aligned disks have nearly uniform eccentricity profiles.

Stabilized disks suppress tidal disruption events.

Abstract

The nucleus of our nearest, large galactic neighbor, M31, contains an eccentric nuclear disk--a disk of stars on eccentric, apsidally-aligned orbits around a supermassive black hole (SMBH). Previous studies of eccentric nuclear disks considered only an isolated disk, and did not study their dynamics under galaxy mergers (particularly a perturbing SMBH). Here, we present the first study of how eccentric disks are affected by a galactic merger. We perform N-body simulations to study the disk under a range of different possible SMBH initial conditions. A second SMBH in the disk always disrupts it, but more distant SMBHs can shut off differential precession and stabilize the disk. This results in a more aligned disk, nearly uniform eccentricity profile, and suppression of tidal disruption events compared to the isolated disk. We also discuss implications of our work for the presence of a secondary SMBH in M31.