[OIII] emission in z=2 quasars with and without Broad Absorption Lines

TL;DR

This study compares [OIII] emission in quasars with and without Broad Absorption Lines to understand outflow mechanisms, finding that outflow properties are similar across different quasar types once CIV emission effects are considered.

Contribution

It provides new near-infrared spectra and a comprehensive analysis linking optical and ultraviolet outflow signatures in a large quasar sample, supporting a unified outflow model.

Findings

[OIII] strength correlates with CIV emission properties.

No significant difference in [OIII] between BAL and non-BAL quasars after accounting for CIV.

BALs are likely intermittent tracers of persistent quasar outflows.

Abstract

Understanding the links between different phases of outflows from active galactic nuclei is a key goal in extragalactic astrophysics. Here we compare [OIII] $\lambda\lambda$4960,5008 outflow signatures in quasars with and without Broad Absorption Lines (BALs), aiming to test how the broad absorption troughs seen in the rest-frame ultraviolet are linked to the narrow line region outflows seen in the rest-frame optical. We present new near-infrared spectra from Magellan/FIRE which cover [OIII] in 12 quasars with 2.1 < z < 2.3, selected to have strong outflow signatures in CIV $\lambda$1550. Combining with data from the literature, we build a sample of 73 BAL, 115 miniBAL and 125 non-BAL QSOs with 1.5 < z < 2.6. The strength and velocity width of [OIII] correlate strongly with the CIV emission properties, but no significant difference is seen in the [OIII] emission-line properties between the BALs, non-BALs and miniBALs once the dependence on CIV emission is taken into account. A weak correlation is observed between the velocities of CIV BALs and [OIII] emission, which is accounted for by the fact that both outflow signatures correlate with the underlying CIV emission properties. Our results add to the growing evidence that BALs and non-BALs are drawn from the same parent population and are consistent with a scenario wherein BAL troughs are intermittent tracers of persistent quasar outflows, with a part of such outflow becoming optically thick along our line-of-sight for sporadic periods of time within which BALs are observed.