Super-Eddington Quasars as Cosmological Probes

Our understanding of the composition, dynamics, and structure of the Universe relies on accurate distance measurements. Quasars, observed up to z.le.7.6, offer the potential to characterize the matter and energy content of the Universe across multiple cosmic epochs and to bridge the gap between the late and early Universe. Quasars radiating close to the Eddington limit tend to saturate toward a limiting value, where the luminosity-to-mass ratio (L/M) becomes constant, enabling luminosity to be expressed in terms of the virial velocity field of the BLR (L propto FWHM 4). Hbeta is a reliable virial estimator, however, it becomes inaccessible at z.ge.0.8 to most ground-based telescopes. In the UV range, Al III 1860 seems to be the best candidate, due to its similar kinematics to Hbeta. The use of AlIII 1860 allows us to include sources at higher redshift observed by near-infrared instruments. Through the characterization of the 1900 blend (including AlIII 1860, SiIII] 1892, CIII] 1909, and UV FeIII), we have identified a sample of super-Eddington AGN at 4.le.z.le.7 from VLT, Gemini, and Keck telescopes. In this talk, we will present a preliminary Hubble diagram of super-Eddington AGN at 0.le.z.le.7, including observations from AlIII 1860 and Hbeta. We will also present caveats of the method and discuss future improvements.