Nonuniform cosmological birefringence and active galactic nuclei

Marc Kamionkowski California Institute of Technology, Mail Code 350-17, Pasadena, California 91125, USA (Received 21 April 2010; revised manuscript received 28 April 2010; published 25 August 2010) The CMB constrains the cosmological-birefringence rotation angle to be j j & 1 (1 ) out to redshifts z ’ 1100 for a rotation that is uniform across the sky. However, the rotation angle ð ; Þ may vary with position ð ; Þ on the sky, and if so, then it can be sought in current and future active galactic nuclei data. An upper limit h 2i1=2 & 3:7 to the scatter in the position-angle–polarization offsets in a sample of only N 1⁄4 9 active galactic nuclei already constrains the rotation spherical-harmonic coefficients to ð4 Þ 1=2 lm & 3:7 and constrains the power spectrum for in models where it is a stochastic field. Future constraints can be improved with more sources and by analyzing well-mapped sources with a tensor-harmonic decomposition of the polarization.