The central structure of Broad Absorption Line QSOs: observational characteristics in the cm-mm wavelength domain

TL;DR

This study investigates the properties of Broad Absorption Line QSOs in the radio and millimeter wavelengths, revealing diverse orientations and morphologies that challenge simple evolutionary or orientation models.

Contribution

It provides a comprehensive multi-wavelength observational analysis of Radio-Loud BAL QSOs, including high-resolution VLBI imaging and dust component searches.

Findings

BAL QSOs show diverse morphologies and orientations.

Results do not support a uniformly young age for BAL QSOs.

Outflows can have various angles relative to the jet axis.

Abstract

Accounting for ~20% of the total QSO population, Broad Absorption Line QSOs are still an unsolved problem in the AGN context. They present wide troughs in the UV spectrum, due to material with velocities up to 0.2 c toward the observer. The two models proposed in literature try to explain them as a particular phase of the evolution of QSOs or as normal QSOs, but seen from a particular line of sight. We built a statistically complete sample of Radio-Loud BAL QSOs, and carried out an observing campaign to piece together the whole spectrum in the cm wavelength domain, and highlight all the possible differences with respect to a comparison sample of Radio-Loud non-BAL QSOs. VLBI observations at high angular resolution have been performed, to study the pc-scale morphology of these objects. Finally, we tried to detect a possible dust component with observations at mm-wavelengths. Results do not seem to indicate a young age for all BAL QSOs. Instead a variety of orientations and morphologies have been found, constraining the outflows foreseen by the orientation model to have different possible angles with respect to the jet axis.