A New Probe of Cosmic Birefringence Using Galaxy Polarization and Shapes

TL;DR

This paper introduces a new statistical approach using galaxy polarization and shapes to measure cosmic birefringence, aiming to detect parity violation from axions with high precision.

Contribution

It presents an unbiased minimum-variance estimator for the rotation angle based on galaxy polarization-shape correlation, enhancing cosmic birefringence measurement techniques.

Findings

Estimator achieves 5°--15° uncertainty per galaxy.

Galaxy surveys can outperform CMB experiments in rotation angle noise.

Method offers a new probe for parity violation in the universe.

Abstract

We propose a novel statistical method to measure cosmic birefringence and demonstrate its power in probing parity violation due to axions. Exploiting an empirical correlation between the integrated radio polarization direction of a spiral galaxy and its apparent shape, we devise an unbiased minimum-variance estimator for the rotation angle, which should achieve an uncertainty of $5^\circ$--$ 15^\circ$ per galaxy. Large galaxy samples from the forthcoming SKA continuum surveys, together with optical shape catalogs, promise a comparable or even lower noise power spectrum for the rotation angle than in the CMB Stage-IV (CMB-S4) experiment, with different systematics.