Abstract

We analyse the properties of a sample of polarized radio galaxies with a wide range of redshifts. Our results suggest that a large fraction of UV light in distant radio galaxies is scattered anisotropic nuclear radiation.

Introduction

High redshift radio galaxies (HZRGs) have elongated morphologies (emission lines and continuum) aligned with the radio axis. The alignment of the continuum is strong in the ultraviolet and weak in the infrared around 1µ (rest frame) [2]. While the IR round component can be explained with an evolved stellar population, the nature of the UV aligned component is still a matter of debate. Two origins have been proposed for the UV light : (a) star formation induced in the ISM by the radio jet (b) dust/electron scattering of anisotropic nuclear light. We present new data which show that at least a considerable fraction of the UV light is not stellar.

The sample and the correlations

We have collected a sample of 41 radio galaxies with 0.1≤z≤1.2 taken from our survey ([1]) and from the literature. We find that the degree of linear polarization P increases with redshift and with the total radio power at 178 MHz (Pr), while it decreases with the rest frame wavelength of the observation (λrest). The main problem in the interpretation of these correlations is that the quantities z−Pr−λrest are interdependent and it is not possible to clarify which correlations are intrinsic and which derived.