Unveiling the Eigenvector 1 UV Sequence in BZQ Blazars: Mg II and Fe II as Diagnostics Tools

We compare the UV Eigenvector 1 (E1) properties of three AGN populations—non-radio QSOs, FRII-Qs, and BZQs—using MgII and FeII UV measurements from SDSS combined with Roma BZCAT classifications. Uniform selection and bootstrap resampling ensure statistically robust comparisons. We analyze the FWHM(MgII) and RFe distributions using Welch's t-test, Ander son–Darling, and Kolmogorov–Smirnov statistics, complemented by ECDFs and boxplots. BZQs show systematically narrower Mg II line widths than FRII-Qs, consistent with smaller viewing an gles along the jet axis. QSOs exhibit the highest median RFe values, whereas FRII-Qs and BZQs occupy intermediate-to-low RFe regimes. Although BZQs span a broad parameter range, their cen tral RFe values remain below those of QSOs, indicating they do not reach the high-RFe end of the Population A sequence. These trends indicate that orientation dominates Mg II kinematics, while intrinsic properties related to black hole mass and accretion rate shape RFe. Our results highlight the diagnostic power of the UV E1 plane at intermediate and high redshift for distinguishing ther mally and jet-dominated AGN populations.