4:00–5:00 pm Zoom Room
Minghao Guo, Peking University, "Hunting for Wandering Massive Black Holes"
In this talk, I will present results of an investigation of low-density accretion flows onto massive black holes (BHs) orbiting around in the outskirts of their host galaxies. (https://arxiv.org/abs/2006.08203)
Those wandering BHs are populated via ejection from the galactic nuclei through multibody BH interactions and gravitational wave recoils associated with galaxy and BH coalescences. From 3D hydrodynamical simulations, we find that when a wandering BH is fed with hot and diffuse plasma with density fluctuations, the mass accretion rate is limited at ∼10%–20% of the canonical Bondi–Hoyle–Littleton rate owing to a wide distribution of inflowing angular momentum. We further calculate radiation spectra from radiatively inefficient accretion flows onto the wandering BH using a semi-analytical two-temperature disk model and find that the predicted spectra have a peak at the millimeter band, where the ALMA has the highest sensitivity and spatial resolution. Millimeter observations with ALMA and future facilities such as ngVLA will enable us to hunt for a population of wandering BHs and push the detectable mass limit down to M_BH~2e7 Msun for massive nearby ellipticals, e.g., M87, and M_BH~1e5 Msun for the Milky Way. This radiation spectral model, combined with numerical simulations, will be applied to give physical interpretations of off-nuclear BHs detected in dwarf galaxies, which may constrain BH seed formation scenarios.