Interpretation of the global anisotropy in the radio polarizations of cosmologically distant sources

Abstract

We present a detailed statistical study of the observed anisotropy in radio polarizations from distant extragalactic objects. This anisotropy was earlier found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger data set. A very strong signal was seen after imposing the cut % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC% vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz% ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb% L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe% pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam% aaeaqbaaGcbaGaeiiFaWNaemOuaiLaemyta0KaeyOeI0Yaa0aaaeaa% cqWGsbGucqWGnbqtaaGaeiiFaWNaeyOpa4JaeGOnaydcbaGae8NCai% Nae8xyaeMae8hzaqMae83la8Iae8xBa02aaWbaaSqabeaacqWFYaGm% aaaaaa!4CC9! $$|RM - \overline {RM} | > 6rad/m^2 $$ , whereRM is the rotation measure and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC% vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz% ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb% L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe% pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam% aaeaqbaaGcbaWaa0aaaeaacqWGsbGucqWGnbqtaaaaaa!3D2C! $$\overline {RM} $$ its mean value. In this paper, we show that there are several indications that this anisotropy cannot be attributed to bias in the data. We also find that a generalized statistic shows a very strong signal in the entire data without imposing theRM dependent cut. Finally we argue that an anisotropic background pseudoscalar field can explain the observations.