2020/06/29 by Jenny E. Greene, Jay Strader, Luis C. Ho · 62 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena
paper · doi:10.1146/annurev-astro-032620-021835
openalex created_date 2019/12/05 · openalex publication_date 2020/06/29 · openalex updated_date 2026/07/28
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 with large scatter. We believe the scatter is at least partially driven by a broad range in black hole masses, because the occupation fraction appears to be relatively high in these galaxies. ▪ We fold the observed scaling relations with our empirical limits on occupation fraction and the galaxy mass function to put observational bounds on the black hole mass function in galaxy nuclei. ▪ We are pessimistic that local demographic observations of galaxy nuclei alone could constrain seeding mechanisms, although either high-redshift luminosity functions or robust measurements of off-nuclear black holes could begin to discriminate models.