The Eddington ratio is a key parameter that governs the diversity of quasar properties. It can be scaled with a strong anticorrelation between optical Fe IIopt and [O III] emission. In search of such indicators in the far-UV band, the Hubble Space Telescope far-UV spectra of 150 low-redshift quasars are analysed in combination with their optical SDSS counterparts. The strength of Fe II+Fe III λ1123 emission is significantly correlated with that of Fe IIopt. A moderate correlation may also exist between Fe II λ1071 and Fe IIopt. The finding opens the possibility that far-UV Fe II emission may serve as a new gauge of the Eddington ratios. The high- and low-ionization lines in the far-UV band display different patterns: for the quasars with higher Eddington ratios, the low-ionization UV lines are stronger, and the high-ionization lines are broader and weaker.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- September 2021
- quasars: emission line;
- quasars: general;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- To appear in MNRAS, with 9 figures and 4 tables