The identification of super-Eddington massive black holes

We present selection criteria for identifying super-Eddington supermassive black hole candidates based on their location along the Eigenvector 1 (E1) main sequence. Our methodology involves a multi-parametric analysis of large AGN samples, combining optical spectroscopic data with multi wavelength diagnostics. We define selection thresholds based on quantitative measures of Fe II/Hβ ratios (where as a tracer for Fe II we consider the emission of the optical blend centered at 4570 ˚ A), [O III]λλ4959,5007 line intensities, CIVλ1549 equivalent widths and shifts, UV diagnostic intensity ratios involving the lines of AlIIIλ1860, SiIII]λ1892, CIII]λ1909, soft- and hard- X-ray photon in dexes. We assess how these parameters scale with the inferred Eddington ratio. We deduce that 62 AGN occupying the extreme end of the E1 main sequence, characterized by the most pronounced Fe II emission, are also the most promising candidates for super-Eddington accretion as they converge toward extreme values of the observed multi-frequency parameters and a limiting Eddington ratio of order unity. Photoionization modeling is then used to validate our empirical criteria over a broad range of cosmic epochs.