Revisiting the NVSS number count dipole

TL;DR

This paper models the NVSS radio galaxy dipole using mock catalogs within $ ext{Lambda}$CDM, finding that local structures and galaxy bias significantly influence the observed dipole, with some tension remaining at higher flux thresholds.

Contribution

It provides a realistic, $ ext{Lambda}$CDM-based modeling of the NVSS dipole, incorporating galaxy bias and local structure effects, and compares predictions with observations.

Findings

Most of the dipole signal (70%) is due to local structures within $z\lesssim0.1$.

The bias factor $b$ influences the dipole amplitude and varies with flux threshold.

Tension between model and observed dipole persists at higher flux thresholds, around 3 sigma.

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.