The Relationship Between Emission Line and Continuum Luminosity and the Baldwin Effect in Blazars. I. The Case of the Mg II {\lambda}2798 {\AA} Emission Line

TL;DR

This study examines the Mg II emission line and continuum luminosity relationship in quasars and blazars, revealing differences in the Baldwin Effect and suggesting diverse ionization mechanisms and accretion disk properties.

Contribution

It provides a refined empirical analysis of the Mg II-3000 Å correlation, accounting for variability, and explores the physical origins of the Baldwin Effect in different AGN types.

Findings

Significant slope differences between RQ quasars and FSRQs in line-continuum relation

A substantial fraction of sources exhibit NTD < 1, indicating complex ionization mechanisms

The Baldwin Effect naturally arises from the line-continuum luminosity relationship

Abstract

Aims. This study investigates the relationship between the Mg II {\lambda}2798 {\AA} emission line and the 3000 {\AA} continuum luminosity, as well as the Baldwin Effect, in a sample of 40,685 radio-quiet (RQ) quasars and 441 Flat Spectrum Radio Quasars (FSRQs). Methods. We perform a comprehensive re-evaluation of the Mg II-3000 {\AA} correlation, explicitly accounting for dispersion introduced by AGN variability. After excluding >3000 radio-loud sources, we employ a binning technique to mitigate variability effects, yielding a refined empirical relation. We also further examine the Non-Thermal Dominance (NTD) parameter, to investigate the dominant source of the continuum. Results. Our analysis reveals statistically significant differences in the slopes of the line-continuum luminosity relation between RQ quasars and FSRQs, with a parallel discrepancy in the Baldwin Effect. These findings imply either (1) intrinsic differences in the accretion disk spectra of RQ AGNs and FSRQs or (2) jet-induced continuum emission in FSRQs contributing to Broad Line Region (BLR) ionization. We also found that a substantial fraction of both RQ quasars (43.8\%) and blazars (55.5\%) exhibit NTD < 1. For blazars, this suggests that the accretion disk alone cannot fully explain BLR ionization; while we interpret NTD < 1 in radio-quiet quasars as a signature of several physical mechanisms: anomalies in the BLR structure (such as outflow or inflows), time lags between continuum and line variations, and the suppression of the UV continuum by a strong corona that diverts accretion power. Finally, we demonstrate that the Baldwin Effect emerges naturally from the line-continuum luminosity relationship, requiring no additional physical mechanism to explain its origin