Wandering Supermassive Black Holes in Milky Way Mass Halos

Understand

We present a self-consistent prediction from a large-scale cosmological simulation for the population of `wandering' supermassive black holes (SMBHs) of mass greater than $10^6$ M$_{\odot}$ on long-lived, kpc-scale orbits within Milky Way (MW)-mass galaxies.

• We extract a sample of MW-mass halos from the Romulus25 cosmological simulation (Tremmel et al.
• 2017), which is uniquely able to capture the orbital evolution of SMBHs during and following galaxy mergers.
• We predict that such halos, regardless of recent merger history or morphology, host an average of $5.1 \pm 3.3$ SMBHs, including their central black hole, within 10 kpc from the galactic center and an average of $12.2 \pm 8.4$ SMBHs total within their virial radius, not counting those in satellite halos.