Extended radio emission in MOJAVE Blazars: Challenges to Unification

TL;DR

This study analyzes 1.4 GHz radio emissions in MOJAVE blazars, revealing complex jet properties and challenging simple unification models by showing diverse morphologies and correlations between radio power and jet speeds.

Contribution

It provides new insights into the relationship between radio emission, jet speeds, and morphology, questioning traditional blazar classifications and unification schemes.

Findings

Extended radio emission correlates with jet speeds.

Many BL Lacs have FRII-like morphology and power.

Quasars show intermediate radio powers.

Abstract

We present the results of a study on the 1.4 GHz kpc-scale radio emission in the complete flux density limited MOJAVE sample, comprising 135 radio-loud AGNs. While extended emission is detected in the majority of the sources, about 7% of the sources exhibit only radio core emission. Many BL Lacs exhibit extended radio power and kpc-scale morphology typical of powerful FRII jets, while a substantial number of quasars possess radio powers intermediate between FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme, which links BL Lacs to FRIs and quasars to FRIIs. We find a significant correlation between extended radio emission and pc-scale jet speeds: the more radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or low frequency) radio emission is indeed related to jet kinetic power. Various properties such as extended radio power and apparent pc-scale jet speeds vary smoothly between different blazar subclasses, suggesting that, at least in terms of radio jet properties, the distinction between quasars and BL Lac objects, at an emission-line equivalent width of 5 Angstrom is essentially an arbitrary one. Based on the assumption that the extended radio luminosity is affected by the kpc-scale environment, we define the ratio of extended radio power to absolute optical magnitude as a proxy for environmental effects. Trends with this parameter suggest that the pc-scale jet speeds and the pc-to-kpc jet misalignments are not affected by the large-scale environment, but are more likely to depend upon factors intrinsic to the AGN, or its local pc-scale environment. We suggest that some of the extremely misaligned MOJAVE blazar jets could be "hybrid" morphology sources, with an FRI jet on one side and an FRII jet on the other. (Abridged)