Radio Polarization: A Powerful Resource for Understanding the Blazar Divide

TL;DR

This study uses high-sensitivity radio polarimetry to analyze blazar subclasses, revealing differences in polarization structures and suggesting both intrinsic and extrinsic factors influence their characteristics, with implications for the FR dichotomy.

Contribution

It provides new insights into blazar subclasses through detailed radio polarimetric observations, highlighting the roles of intrinsic and extrinsic variables in their formation.

Findings

RL quasars show extensive polarization in cores, jets, lobes, hotspots

BL Lacs exhibit polarization mainly in cores and inner jets

Many PG quasars are restarted, distorted, or hybrid FR morphologies

Abstract

With high-sensitivity kiloparsec-scale radio polarimetry, we can examine the jet-medium interactions and get a better understanding of the blazar divide in radio-loud (RL) AGN. We are analyzing the radio polarimetric observations with the EVLA and GMRT of 24 quasars and BL Lacs belonging to the Palomar-Green (PG) sample. The RL quasars show extensive polarisation structures in their cores, jets, lobes, and hotspots, whereas preliminary results suggest that BL Lacs exhibit polarisation primarily in their cores and inner jet regions. These findings imply that both intrinsic (central engine-related) and extrinsic (environment-related) variables are important in the formation of the blazar subclasses. The Fanaroff-Riley (FR) dichotomy can also be studied assuming RL unification and looking through the lens of blazars. Due to the radio-unbiased nature of the optically/UV-selected PG sample, we find a large fraction of the PG quasars are restarted, distorted (S- or X-shaped), or have a hybrid FR morphology.