2011/11/30 by Francesco Shankar, David H. Weinberg, Jordi Miralda‐Escudé +1 · 207 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astronomy #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics #Binary black hole #Black hole (networking) #Eddington luminosity #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Gravitational wave #Lambda #Physics #Quantum mechanics #Redshift #Supermassive black hole #astro-ph.CO
paper · pdf · doi:10.1093/mnras/sts026
published in Monthly Notices of the Royal Astronomical Society 428(1), 421-446 (Oxford University Press) · 29 pages, 16 Figures, 2 Tables. Replaced with version accepted by MNRAS. Improved presentation
arxiv created 2012/09/18 · openalex publication_date 2012/10/23 · arxiv updated 2015/06/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/08
We develop semi-empirical models of the supermassive black hole and active galactic nucleus (AGN) populations, which incorporate the black hole growth implied by the observed AGN luminosity function assuming a radiative efficiency ϵ and a distribution of Eddington ratios λ. By generalizing these continuity-equation models to allow a distribution P(λ | MBH, z), we are able to draw on constraints from observationally estimated λ distributions and active galaxy fractions while accounting for the luminosity thresholds of observational samples. We consider models with a Gaussian distribution of log λ and Gaussians augmented with a power-law tail to low λ. Within our framework, reproducing the high observed AGN fractions at low redshift requires a characteristic Eddington ratio λc that declines at late times, and matching observed Eddington ratio distributions requires a P(λ) that broadens at low redshift. To reproduce the observed increase of AGN fraction with black hole or galaxy mass, we also require a λc that decreases with increasing black hole mass, reducing the AGN luminosity associated with the most massive black holes. Finally, achieving a good match to the high-mass end of the local black hole mass function requires an increased radiative efficiency at high black hole mass. We discuss the potential impact of black hole mergers or a λ-dependent bolometric correction, and we compute evolutionary predictions for black hole and galaxy specific accretion rates. Despite the flexibility of our framework, no one model provides a good fit to all the data we consider; it is particularly difficult to reconcile the relatively narrow λ distributions and low duty cycles estimated for luminous broad-line AGN with the broader λ distributions and higher duty cycles found in more widely selected AGN samples, which typically have lower luminosity thresholds.