Exploring the Ultraviolet Quasar Main Sequence and Its Connection to the Eddington Ratio.

The Quasar Main Sequence (MS) in the optical regime organizes the phenomenology of the broad emission lines in quasars, providing an ordered change of the broad line region (BLR), primarily governed by the Eddington ratio. This work explores whether this trend extends to the UV regime. Using a sample of 80 low-z ( z < 1 ) HST UV spectra (with known optical MS parameters), we found a UV MS using the FWHM of Al III ?1860 and the UV FeIII centered at 2080Å. We also analyzed a sample of 70 UV high-z (4 < z < 7) quasars, from VLT, Gemini, and Keck observations. Our results show that UV FeIII emission positively correlates with the Eddington ratio independently of the redshift range. This allows us to set an empirical threshold based on the equivalent width of UV FeIII to identify super-Eddington AGN. This methodology can be applied to search for super-Eddington AGN in ground-based surveys such as SDSS and DESI. Also, it opens the discussion around the emitting zone of the iron ions in the BLR and their close relation with the Eddington ratio.