Accretion of gaseous disks at high redshifts and the depolarization asymmetry of radio-loud quasars

Abstract

Anewscenario is explored to understand the striking depolarization asymmtery observed between the two lobes of powerful radio sources exhibiting one-sided jets. According to this tight correlation, commonly known as the Laing-Garrington effect, the lobe on the counter-jet side is found to depolarize more rapidly at longer radio wavelengths, compared to the opposite lobe. Conventionally, this is explained by postulating that distant radio sources are embedded within large halos of dense magneto-ionic plasma, with typical dimensions of the core of intra-cluster medium (ICM). Pointing out potential problems with this scheme, we argue that the depolarization asymmetry, instead of arising from the putative ICM cores at high redshifts, could occur more commonly due to extended disks of dusty magneto-ionic medium surrounding elliptical galaxies hosting quasars. Differring radically in their physical origin from the postulated ICM haloes, such disks are likely to have been acquired in the events of capture of gas-rich galaxies, or their progenitors, by massive radio-loud ellipticals. Radio and optical evidences for such disks are summarized and some aspects of their evolution are briefly discussed.