SUPER-EDDINGTON ACCRETION IN ACTIVE GALACTIC NUCLEI

Supermassive black holes at the cores of galaxies blast radiation and ultra-fast winds outward, as illustrated in this artist's conception. Credit: NASA/JPL-Caltech

Broad emission lines are a hallmark feature of type 1 active galactic nuclei (AGNs) and quasars. Many basic properties of the broad-line region (BLR), such as its basic geometry, dynamics, and physical connection to the accretion disk around the supermassive black hole (BH), remain illdefined. AGN spectra exhibit both tremendous diversity as well as discernable patterns of systematic regularity.

In a recent paper (Du, Wang et al. 2016) published on ApJL, the authors study correlations among three dimensionless AGN parameters: accretion rate (or Eddington ratio), shape of the broad Hβ line, and flux ratio of optical Fe II to Hβ. A strong correlation among them is found, denoted as the fundamental plane of AGN BLRs. The BLR fundamental plane allows to conveniently explore the accretion status of the AGN central engine using single-epoch spectra, opening up many interesting avenues for exploring AGNs, including their cosmological evolution. The authors apply the plane to a sample of z < 0.8 quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.

(The Eddington limit, is the maximum luminosity a body - such as a star - can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The state of balance is called hydrostatic equilibrium. When a star exceeds the Eddington limit, it will initiate a very intense radiation-driven stellar wind from its outer layers).

▪ Du, Wang et al., 2016 ApJL - The Fundamental Plane of the Broad-line Region in Active Galactic Nuclei (arXiv)

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