Main trends of the quasar main sequence -- effect of viewing angle

TL;DR

This paper models how viewing angle and BLR geometry influence quasar properties along the main sequence, using photoionization simulations to explain observed emission trends and diversity.

Contribution

It introduces a comprehensive modeling approach that accounts for viewing angle and BLR geometry effects, explaining quasar diversity and emission features along the main sequence.

Findings

Dependence of FeII emission strength on L_bol/L_Edd ratio

Explanation of the rarity of extreme xA sources

Predictive modeling for reverberation mapping studies

Abstract

We address the effect of the viewing angle of the accretion disk plane and the geometry of the broad-line region (BLR) with the goal of interpreting the distribution of quasars along the main sequence (MS). We utilize photoionization code CLOUDY to model the BLR FeII emission, incorporating the grossly underestimated role of the form factor (f). We recover the dependence of the strength of the FeII emission in the optical (R$_{\rm{FeII}}$) on L$_{\rm{bol}}$/L$_{\rm{Edd}}$ ratio and related observational trends - as a function of the spectral energy distribution (SED) shape, cloud density, composition and intra-cloud dynamics, assumed following prior observational constraints. With this approach, we are now able to explain the diversity of quasars and the change of the quasar properties along the Main Sequence (MS). Our approach also explains the rarity of the highest FeII emitters known as the extreme xA sources and can be used as a predictive tool in future reverberation mapping studies of Type-1 AGNs. This approach further justifies the use of quasars as `cosmological probes'.