The unification of powerful quasars and radio galaxies and their relation to other massive galaxies

TL;DR

This study uses infrared data from Herschel and Spitzer to test the unification model of powerful radio galaxies and quasars, confirming that their far-infrared properties are orientation-invariant and can differentiate active galaxies from star-forming ones.

Contribution

It provides observational evidence supporting the unification model through infrared color analysis and extends the model to include radio-quiet active galaxies.

Findings

Radio galaxies and quasars have similar far-infrared colors.

Mid-infrared colors depend on orientation.

Infrared colors distinguish active galaxies from star-forming galaxies.

Abstract

The unification model for powerful radio galaxies and radio-loud quasars postulates that these objects are intrinsically the same but viewed along different angles. Herschel Space Observatory data permit the assessment of that model in the far-infrared spectral window. We analyze photometry from Spitzer and Herschel for the distant 3CR hosts, and find that radio galaxies and quasars have different mid-infrared, but indistinguishable far-infrared colors. Both these properties, the former being orientation dependent and the latter orientation invariant, are in line with expectations from the unification model. Adding powerful radio-quiet active galaxies and typical massive star-forming galaxies to the analysis, we demonstrate that infrared colors not only provide an orientation indicator, but can also distinguish active from star-forming galaxies.