BALQSO Spectra Explained by Shock Disruption of Galactic Clouds

TL;DR

This paper demonstrates through hydrodynamical simulations that AGN winds disrupting interstellar clouds can produce the broad absorption lines observed in quasar spectra, explaining the origin of BAL features.

Contribution

It introduces a novel hydrodynamical model showing how shock disruption of galactic clouds by AGN winds creates high-speed absorbing clouds, accounting for BAL phenomena.

Findings

High-velocity absorption features up to 3000 km/s can be produced.

Disruption of clouds by winds at 0.1c explains observed BAL velocities.

Cloud density and wind speed determine absorption line properties.

Abstract

Blue-shifted Broad Absorption Lines (BALs) detected in quasar's spectra are indicative of AGN outflows. We show, using 2D hydrodynamical simulations, that disruption of interstellar clouds by a fast AGN wind can lead to formation of cold, dense high speed blobs that give rise to broad absorption features in the transmission spectrum of the AGN continuum source. For a wind velocity of $0.1 c$ and sufficiently high cloud density ($n_{c}$ < $10^4$ cm$^{-3}$, depending on size), absorption troughs with velocities up to about $3000$ km s$^{-1}$ can be produced. For slower winds and/or lower cloud density the anticipated velocity of the absorbing clouds should be smaller.