The picture of BLR in 2.5-D FRADO: Dynamics & Geometry

TL;DR

This paper investigates the dynamics and geometry of the Broad Line Region in active galaxies, showing that radiation pressure on dusty clouds can cause outflows whose characteristics depend on the Eddington ratio.

Contribution

It introduces a non-hydrodynamical model of BLR cloud dynamics considering radiation pressure and dust opacity, revealing outflow behavior and geometry dependence on Eddington ratio.

Findings

Radiation pressure can drive dusty cloud outflows from the accretion disk surface.

BLR dynamics vary with Eddington ratio, affecting velocity fields and cloud geometry.

Vertical velocities are larger in high Eddington ratio sources, influencing emission regions.

Abstract

The dynamics of the Broad Line Region (BLR) in Active galaxies is an open question, direct observational constraints suggest a predominantly Keplerian motion, with possible traces of inflow or outflow. In this paper we study in detail the physically motivated BLR model of (Czerny & Hryniewicz, 2011) based on the radiation pressure acting on dust at the surface layers of accretion disk (AD). We consider here a non-hydrodynamical approach to the dynamics of the dusty cloud under the influence of radiation coming from the entire AD. We use here the realistic description of the dust opacity, and we introduce two simple geometrical models of the local shielding of the dusty cloud. We show that the radiation pressure acting on dusty clouds is strong enough to lead to dynamical outflow from the AD surface, so the BLR has a dynamical character of (mostly failed) outflow. The dynamics strongly depend on the Eddington ratio of the source. Large Eddington ratio sources show a complex velocity field and large vertical velocities with respect to the AD surface, while for lower Eddington ratio sources vertical velocities are small and most of the emission originates close to the AD surface. Cloud dynamics thus determines the 3-D geometry of the BLR.