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. This study is motivated by the puzzling signal of alignment of polarizations from distant quasars at optical frequencies. We use a coordinate invariant measure of dispersion to test for alignment of polarizations of widely separated sources. The data from JVAS/CLASS 8.4 GHz surveys are used for our study. We find that the data set with polarization flux greater than 1 mJy shows a significant signal of alignment at distance scales of order 150 Mpc. The significance of alignment decreases as we go to larger distances. In contrast the data set with polarization flux less than 1 mJy does not show significant alignment at short distances. However this set, as well as the full data sample, shows a very significant signal at large distances of order 500-850 Mpc. Due to the presence of relatively large error in the low polarization sample, this signal needs to be tested further with more refined data. We also study the signal by imposing a cut on the error in polarization. We find that the significance of alignment increases with decrease in fractional error. We are unable to attribute our results to known sources of bias. We discuss a possible physical explanation of our results. Int. J. Mod. Phys. D 2013.22. Downloaded from www.worldscientific.com by CAMBRIDGE UNIVERSITY on 02/07/15. For personal use only. 1350089-3 Int. J. Mod. Phys. D 2013.22. Downloaded from www.worldscientific.com by CAMBRIDGE UNIVERSITY on 02/07/15. For personal use only.

Extracting the spectral index of the intergalactic magnetic field from radio polarizations

“…Another possibility is that sources in a small neighbourhood are observed together within a particular observational run. It is possible that this could generate alignment in sources within small angular separations, as observed in Tiwari & Jain (2013). We cannot rule out such a possibility.…”

“…The polarization data is likely to have large scatter and we use the jackknife estimate of errors. The jackknife errors are found to be large in comparison to the squared variance of alignment statistics of shuffled PAs (Tiwari & Jain 2013). In our earlier determination of the significance of alignment we had used the latter procedure (Tiwari & Jain 2013).…”

“…The jackknife errors are found to be large in comparison to the squared variance of alignment statistics of shuffled PAs (Tiwari & Jain 2013). In our earlier determination of the significance of alignment we had used the latter procedure (Tiwari & Jain 2013). If we instead use the jackknife errors we find that the significance of alignment is reduced.…”

“…This changes the magnitude of S D significantly for small n v but does not change the alignment significance results. However, as already mentioned above, in this paper we are considering the jackknife errors which are significantly larger than the variance of S D for the case of the random polarization samples, considered in our previous paper (Tiwari & Jain 2013). This does lead to an appreciable change in the significance of alignment.…”

Global alignments of parsec-scale AGN radio jets and their polarization planes

“…No significant signal was detected in this sample either. However, Tiwari & Jain (2013) and Pelgrims & Hutsemékers (2016) used largely the same JVAS and CLASS data and presented evidence for the global alignment of polarization vectors in their sample. Moreover, Pelgrims & Hutsemékers (2016) demonstrated that the radio polarization position angles of the quasars are aligned with the axes of the large quasar groups they belong to.…”