2023MNRAS.525.4474M

This paper presents new optical and near-UV spectra of 11 extremely powerful jetted quasars, with radio to optical flux density ratio >10³, which concomitantly cover the low-ionization emission of Mg IIλ2800 and Hβ as well as the Fe II blends in the redshift range 0.35 ≲ z ≲ 1. We aim to quantify broad emission line differences between radio-loud (RL) and radio-quiet (RQ) quasars by using the 4D eigenvector 1 parameter space and its main sequence (MS) and to check the effect of powerful radio ejection on the low-ionization broad emission lines. The Hβ and Mg IIλ2800 emission lines were measured by using non-linear multicomponent fittings as well as by analysing their full profile. We found that broad emission lines show large redward asymmetry both in Hβ and Mg IIλ2800. The location of our RL sources in a UV plane looks similar to the optical one, with weak Fe II_UV emission and broad Mg IIλ2800. We supplement the 11 sources with large samples from previous work to gain some general inferences. We found that, compared to RQ, our extreme RL quasars show larger median Hβ full width at half maximum (FWHM), weaker Fe II emission, larger M_BH, lower L_bol/L_Edd, and a restricted bf space occupation in the optical and UV MS planes. The differences are more elusive when the comparison is carried out by restricting the RQ population to the region of the MS occupied by RL sources, albeit an unbiased comparison matching M_BH and L_bol/L_Edd suggests that the most powerful RL quasars show the highest redward asymmetries in Hβ.