Polarization Alignment in JVAS/CLASS flat spectrum radio surveys

Abstract

We present a detailed statistical analysis of the alignment of polarizations of radio sources at high redshift. We use the JVAS/CLASS 8.4-GHz surveys for our study. This study is motivated by the puzzling signal of alignment of polarizations from distant quasars at optical frequencies. We explore several different cuts on the polarization flux for our analysis. We find that the entire data shows a very significant signal of alignment on very large distance scales of order 500 Mpc. The alignment starts to decay only at much larger distances of order Gpc. If we only consider data with polarization flux greater than 1 mJy, we find alignment at distance scales less than 150 Mpc. We also find that data with polarization flux less than 0.5 mJy does not show significant alignment. Similar results are seen for data with degree of polarization less than 0.01, although here a mild signal of alignment is observed for a narrow range of angular separations. We argue that the signal cannot be explained in terms of bias due to systematic errors in removal of instrumental polarization. We also find that the degree of polarization shows a strong negative correlation with the total flux. The data appears to fall into two classes, one of which shows such a correlation. The remaining set, which has total flux greater than 100 mJy and degree of polarization lying between 0.01 and 0.1, shows a more random behaviour. The latter set is also found to show no alignment whereas the first set shows a very strong polarization alignment.