A Polarimetric Study of 9 PG Quasars with the VLA

TL;DR

This study uses VLA polarization imaging at 6 GHz to analyze magnetic field structures, morphologies, and jet properties of 9 PG quasars, revealing correlations between jet power, accretion rates, and polarization.

Contribution

First detailed polarization imaging of PG quasars at 6 GHz, linking magnetic field structures with jet power and accretion rates.

Findings

Polarization detected in cores, jets, and lobes of all quasars.

Hotspots show transverse or complex magnetic fields.

Jet powers correlate with accretion rates.

Abstract

We present polarization images of 9 radio-loud (RL) quasars from the VLA B-array at 6 GHz. These quasars belong to the Palomar-Green (PG) "blazar" sample comprising 16 RL quasars and 8 BL Lac objects. Extensive polarization is detected in the cores, jets and lobes of all the quasars, with cores primarily displaying magnetic (B-) fields transverse to, and jets displaying fields aligned with the jet direction. Hotspots display either transverse B-fields signifying B- field compression at terminal shocks or more complex structures. The fractional polarization in the cores ranges from 1-10% and jets/lobes from 10-40%. Several of the quasars show distorted or hybrid FRI/FRII radio morphologies with indications of restarted AGN activity. We attribute this to the optical/UV selection criteria of the PG sample that remains unbiased at radio frequencies. The in-band spectral indices of the radio cores are relatively flat while they are steep in the hotspots. This is consistent with the polarization structures where the hotspots appear to be locations of jet bends or bow-shocks. We present global properties for the entire PG "blazar" sample. We find that jet powers correlate with accretion rates for the quasars; higher accretion rates result in more powerful radio jets. A correlation between the radio core fractional polarization and the 150 MHz total radio luminosity for the 9 quasars studied here may imply that more organized B-fields at the jet bases lead to higher core fractional polarization and to more powerful radio jets.