Testing the Cosmological Principle in the radio sky

Understand

The Cosmological Principle states that the Universe is statistically isotropic and homogeneous on large scales.

• In particular, this implies statistical isotropy in the galaxy distribution, after removal of a dipole anisotropy due to the observer's motion.
• We test this hypothesis with number count maps from the NVSS radio catalogue.
• We use a local variance estimator based on patches of different angular radii across the sky and compare the source count variance between and within these patches.