Modeling line-driven disk wind for broad absorption lines of quasars

TL;DR

This study models line-driven disk winds in quasars to explain broad absorption lines, finding funnel-shaped winds with specific opening angles and estimating the probability of observing BAL features based on viewing angles.

Contribution

It applies stellar wind theory to quasar disk winds, providing a non-hydrodynamic model that predicts wind structure and BAL quasar probabilities.

Findings

Funnel-shaped winds with 50° opening angle for certain parameters.

BAL quasar probability estimated at 7-11%.

Disk winds are suppressed for low Eddington ratios or very massive black holes.

Abstract

The disk wind, which is powered by the radiation force due to spectral lines (line force), is studied for broad absorption line (BAL) quasars. We investigate the structure of the disk wind based on the non-hydrodynamic method and compare with wind properties inferred from X-ray observations of BAL quasars. In this paper, we apply the stellar wind theory to the initial condition (the mass outflow rate at the base of the wind). We found the funnel-shaped winds with a half opening angle of 50^{circ} for the case of epsilon=0.3-0.9 and M_{BH}=10^{7-8.5}M_odot, where epsilon is the Eddington ratio and M_{BH} is the black hole mass. Thus, the absorption features are observed for an observer of which a viewing angle is around 50^{circ}. A probability of BAL quasars is 7-11%, which is roughly consistent the abundance ratio of BAL quasars, 10-15%. Here, the probability is estimated by the solid angle, that the absorbing features would be detected, divided by 4pi. In contrast, if the Eddington ratio is smaller than 0.01 or if the black hole is very massive, M_{BH} < 10^9M_{odot}, the disk wind is not launched due to the less effective line force. Then, the quasars are identified as non-BAL quasars independently of the observer's viewing angle.