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We investigate low-density accretion flows onto massive black holes (BHs) with masses of $gtrsim 10^5~M_odot$ orbiting around in the outskirts of their host galaxies, performing three-dimensional hydrodynamical simulations. Those wandering BHs are populated via ejection from the galactic nuclei through multi-body BH interactions and gravitational wave recoils associated with galaxy and BH coalescences. We find that when a wandering BH is fed with hot and diffuse plasma with density fluctuations, the mass accretion rate is limited at $sim 10-20%$ 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 Atacama Large Millimeter/submillimeter Array (ALMA) has the highest sensitivity and spatial resolution. Millimeter observations with ALMA and future facilities such as the next generation Very Large Array (ngVLA) will enable us to hunt for a population of wandering BHs and push the detectable mass limit down to $M_bullet simeq 2times10^7~M_odot$ for massive nearby ellipticals, e.g., M87, and $M_bullet simeq 10^5~M_odot$ 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.
The discovery of a persistent radio source coincident with the first repeating fast radio burst, FRB 121102, and offset from the center of its dwarf host galaxy has been used as evidence for a link with young millisecond magnetars born in superlumino
We characterise the population of wandering black holes, defined as those physically offset from their halo centres, in the Romulus cosmological simulations. Unlike most other currently available cosmological simulations, black holes are seeded based
Binary stars that are on close orbits around massive black holes (MBH) such as Sgr A* in the center of the Milky Way are liable to undergo tidal disruption and eject a hypervelocity star. We study the interaction between such a MBH and circular binar
We show that a subdominant component of dissipative dark matter resembling the Standard Model can form many intermediate-mass black hole seeds during the first structure formation epoch. We also observe that, in the presence of this matter sector, th
Black holes are a common feature of the Universe. They are observed as stellar mass black holes spread throughout galaxies and as supermassive objects in their centres. Observations of stars orbiting close to the centre of our Galaxy provide detailed