Polarization asymmetry in CSS sources: Evidence of AGN fuel?

National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007, India

Corresponding author: D. J. Saikia, djs@ncra.tifr.res.in

Received: 3 January 2003
Accepted: 16 April 2003

Abstract

The compact steep spectrum and gigahertz peaked spectrum sources are widely believed to be young radio sources, with ages 10⁶ yr. If the activity in the nucleus is fuelled by the supply of gas, one might find evidence of this gas by studying the structural and polarization characteristics of CSS sources as these evolve through this gas. We present polarization observations of a sample of CSS sources, and combine our results with those available in the literature, to show that CSS sources are more asymmetric in the polarization of the outer lobes compared with the more extended ones. We suggest that this could be possibly due to interaction of the jets with infalling material, which fuels the radio source. We also investigate possible dependence of the polarization asymmetry of the lobes on redshift, since this might be affected by more interactions and mergers in the past. No such dependence is found for the CSS sources, suggesting that the environments on the CSS scales are similar at different redshifts. However, the polarization asymmetry of the oppositely-directed lobes is larger at higher redshifts for the more extended sources, possibly reflecting the higher incidence of interactions in the past.