Intermediate Mass Ratio Inspirals in Milky Way Galaxies

TL;DR

This paper investigates intermediate mass ratio inspirals (IMRIs) originating from dwarf galaxy black holes merging with larger galaxies in Milky Way-like systems, highlighting their significance for gravitational wave detection.

Contribution

It provides the first detailed analysis of IMRI demographics in Milky Way-like galaxies using cosmological simulations, emphasizing their importance for LISA observations.

Findings

Approximately 50% of mergers have mass ratios below 0.04.

Inspiral durations range from 0.5 to 8 Gyr.

Half of the IMRIs may become more circular over time.

Abstract

A consequence of a non-zero occupation fraction of massive black holes (MBHs) in dwarf galaxies is that these MBHs can become residents of larger galaxy halos via hierarchical merging and tidal stripping. Depending on the parameters of their orbits and original hosts, some of these MBHs will merge with the central supermassive black hole in the larger galaxy. We examine four cosmological zoom-in simulations of Milky Way-like galaxies to study the demographics of the black hole mergers which originate from dwarf galaxies. Approximately half of these mergers have mass ratios less than 0.04, which we categorize as intermediate mass ratio inspirals, or IMRIs. Inspiral durations range from 0.5 - 8 Gyr, depending on the compactness of the dwarf galaxy. Approximately half of the inspirals may become more circular with time, while the eccentricity of the remainder does not evolve. Overall, IMRIs in Milky Way-like galaxies are a significant class of black hole merger that can be detected by LISA, and must be prioritized for waveform modeling.