Revisiting the NVSS number count dipole

Abstract

We present a realistic modeling of the dipole component of the projected sky distribution of NVSS radio galaxies. The modeling relies on mock catalogs generated within the context of $\Lambda$CDM cosmology, in the linear regime of structure formation. After removing the contribution from the solar motion, the mocks show that the remaining observed signal is mostly (70\%) due to structures within $z\lesssim0.1$. The amplitude of the model signal depends on the bias factor $b$ of the NVSS mock galaxies. For sources with flux density, $ S> 15 \; \rm mJy$, the bias recipe inferred from higher order moments is consistent with the observed dipole signal at $2.12\sigma$. Flux thresholds above $20 \; \rm mJy$ yield a disagreement close to the $3\sigma $ level. A constant high bias, $b=3$ is needed to mitigate the tension to the $\sim 2.3\sigma$ level.