A polar+equatorial wind model for broad absorption line quasars: I. Fitting the C IV BAL profiles

TL;DR

This study develops a two-component polar+equatorial wind model using Monte Carlo radiative transfer simulations to reproduce and analyze the diverse broad absorption line profiles observed in quasars, shedding light on their wind geometry.

Contribution

It introduces a novel Monte Carlo radiative transfer code for modeling polar+equatorial wind geometries in quasars, successfully reproducing various BAL profiles and revealing wind rotation effects.

Findings

The model reproduces a range of BAL profiles, including complex and P Cygni types.

Some profiles are consistent with a pole-on viewing angle.

Evidence suggests high-velocity wind rotation in certain BAL quasars.

Abstract

Despite all the studies, the geometry of the wind at the origin of the blueshifted broad absorption lines (BAL) observed in nearly 20% of quasars still remains a matter of debate. We want to see if a two-component polar+equatorial wind geometry can reproduce the typical BAL profiles observed in these objects. We built a Monte Carlo radiative transfer code (called MCRT) to simulate the line profiles formed in a polar+equatorial wind in which the photons, emitted from a spherically symmetric core are resonantly scattered. Our goal is to reproduce typical C IV line profiles observed in BAL quasars and to identify the parameters governing the line profiles. The two-component wind model appears to be efficient in reproducing the BAL profiles from the P Cygni-type profiles to the more complex ones. Some profiles can also be reproduced with a pole-on view. Our simulations provide evidence of a high-velocity rotation of the wind around the polar axis in BAL quasars with non P Cygni-type line profiles.