Limits on global cosmic birefringence using radio sources

Limits on global cosmic birefringence using radio sources
Richard A. Battye, Neal Jackson, Ian Browne
arXiv:2607.02664v1 Announce Type: new
Abstract: We have made measurements of the difference between the position angle (PA) on the sky and the polarization position angle (PPA) of radio sources using data from a combination of the Radio Fundamental Catalogue (RFC) across a range of frequencies between 2.7 and 15~GHz and Cosmic Lens All Sky Survey (CLASS) which observes polarization at 8.4~GHz (X-band). For the 2111 sources with jet PAs measured in the X-band and a known redshift, the distribution is peaked at $approx 0^{circ}$ as expected for no birefringence and it can be modelled by two populations: one which is a Gaussian with mean $mu_{beta}=(0.2pm 1.0)^{circ}$ and standard deviation $sigma_{beta}=(14.7pm 1.1)^{circ}$ and the other a uniform distribution of sources which are a fraction $f_beta=0.72pm 0.02$ of the total. Uncertainties in $mu_beta$ can be reduced to $approx 0.6^{circ}$ by stacking measurements of the PA from other wavebands. We find that limits of $approx 0.1^{circ}$ might be possible with a sample of $sim 10^5$ similarly selected sources and that this could provide a confirmation of recent claims of global birefringence made using the Cosmic Microwave Background observations from the {it Planck} satellite.arXiv:2607.02664v1 Announce Type: new
Abstract: We have made measurements of the difference between the position angle (PA) on the sky and the polarization position angle (PPA) of radio sources using data from a combination of the Radio Fundamental Catalogue (RFC) across a range of frequencies between 2.7 and 15~GHz and Cosmic Lens All Sky Survey (CLASS) which observes polarization at 8.4~GHz (X-band). For the 2111 sources with jet PAs measured in the X-band and a known redshift, the distribution is peaked at $approx 0^{circ}$ as expected for no birefringence and it can be modelled by two populations: one which is a Gaussian with mean $mu_{beta}=(0.2pm 1.0)^{circ}$ and standard deviation $sigma_{beta}=(14.7pm 1.1)^{circ}$ and the other a uniform distribution of sources which are a fraction $f_beta=0.72pm 0.02$ of the total. Uncertainties in $mu_beta$ can be reduced to $approx 0.6^{circ}$ by stacking measurements of the PA from other wavebands. We find that limits of $approx 0.1^{circ}$ might be possible with a sample of $sim 10^5$ similarly selected sources and that this could provide a confirmation of recent claims of global birefringence made using the Cosmic Microwave Background observations from the {it Planck} satellite.