Low- and high-z highly accreting quasars in the 4D Eigenvector 1 context
  Highly accreting quasars are characterized by distinguishing properties in the 4D eigenvector 1 parameter space that make them easily recognizable over a broad range range of redshift and luminosity. The 4D eigenvector 1 approach allows us to define selection criteria that go beyond the restriction to Narrow Line Seyfert 1s identified at low redshift. These criteria are probably able to isolate sources with a defined physical structure i.e., a geometrically thick, optically thick advection-dominated accretion disk (a "slim" disk). We stress that the importance of highly accreting quasars goes beyond the understanding of the details of their physics: their Eddington ratio is expected to saturate toward values of order unity, making them possible cosmological probes. 
Paola Marziani, Jack W. Sulentic, C. Alenka Negrete, Deborah Dultzin,   Mauro D'Onofrio, Ascensi\'on del Olmo, and Mary Loli...
astro-ph.GA