Fluctuations of differential number counts of radio continuum sources

TL;DR

This paper develops a gauge-invariant theoretical framework for analyzing the fluctuations in differential number counts of radio continuum sources, accounting for all linear cosmological perturbations, to improve modeling of galaxy survey data.

Contribution

It introduces a comprehensive, gauge-invariant approach to compute radio source counts including all linear perturbation effects, applicable to future surveys.

Findings

Explicit gauge-invariant expressions derived

Identification of various physical contributions to counts

Framework applicable to modeling angular power spectra

Abstract

We investigate the differential number counts of sources in radio continuum surveys, including all terms at linear order in cosmological perturbations. Our framework does not assume a specific gauge condition. This general approach allows us to recover gauge invariance explicitly. With the complete derivations of the covariant volume integral on the past light cone, we have identified several contributions in the number counts. To clarify their underlying physics, we present each contributions in terms of scalar, vector and tensor modes. This theoretical framework promises to be widely applicable to continuum radio galaxy surveys to model the expected angular power spectrum and two-point correlation.