Intermediate-Mass Black Holes

We describe ongoing searches for intermediate-mass black holes with M BH ≈ 10–10 5 M ⊙ . We review a range of search mechanisms, both dynamical and those that rely on accretion signatures. We find the following conclusions: ▪ Dynamical and accretion signatures alike point to a high fraction of 10 9 –10 10 M ⊙ galaxies hosting black holes with M BH ∼ 10 5 M ⊙ . In contrast, there are no solid detections of black holes in globular clusters. ▪ There are few observational constraints on black holes in any environment with M BH ≈ 100–10 4 M ⊙ . ▪ Considering low-mass galaxies with dynamical black hole masses and constraining limits, we find that the M BH –σ * relation continues unbroken to M BH ∼10 5 M ⊙ , albeit…