Cosmological observations in the radio domain: the contribution of extragalactic sources

TL;DR

This paper reviews how unresolved extragalactic radio sources impact measurements of the cosmic microwave background at low frequencies, emphasizing the importance of source contamination removal for detecting spectral distortions.

Contribution

It provides an updated analysis of extragalactic source contributions to radio sky brightness using recent source count data from 150 MHz to 8.4 GHz.

Findings

Unresolved extragalactic sources significantly affect low-frequency sky brightness.

Updated source counts improve the accuracy of contamination estimates.

The study highlights the importance of source removal for future CMB spectral distortion detection.

Abstract

The low frequency tail of the CMB spectrum, down along the radio range (~1 GHz), may carry weak spectral distortions which are fingerprints of processes occurred during different epochs of the thermal history of the Universe, from z~3\times 10^6 to reionization. TRIS and ARCADE2 are the most recent experiments dedicated to the exploration of this chapter of CMB cosmology. The level of instrumental accuracy they reached in the determination of the absolute sky temperature is such that the removal of galactic and extra-galactic contamination is the true bottleneck towards the recovery of the cosmological signal. This will be certainly the case also for future experiments in the radio domain. Here we present an update of a study originally done to recognize the contribution of unresolved extra-galactic radio sources to the sky brightness measured by TRIS. Despite the specific context which originated our analysis, this is a study of general interest, improved by the inclusion of all the source counts available up-to-date from 150 MHz to 8.4 GHz.