The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky

TL;DR

This paper quantifies the contribution of unresolved extragalactic radio sources to the sky's brightness temperature across a range of frequencies, improving understanding of their spectral behavior and impact on cosmic microwave background measurements.

Contribution

It provides an optimized model of source counts and a detailed spectral analysis of unresolved radio sources' brightness temperature contribution.

Findings

Brightness temperature follows a power law with spectral index ~ -2.7.

Flat spectrum sources become significant above several GHz.

Results aid in separating sky brightness components and assessing CMB temperature.

Abstract

The contribution of the Unresolved Extragalactic Radio Sources to the diffuse brightness of the sky was evaluated using the source number - flux measurements available in literature. We first optimized the fitting function of the data based on number counts distribution. We then computed the brightness temperature at various frequencies from 151 MHz to 8440 MHz and derived its spectral dependence. As expected the frequency dependence can be described by a power law with a spectral index $\gamma \simeq -2.7$, in agreement with the flux emitted by the {\it steep spectrum} sources. The contribution of {\it flat spectrum} sources becomes relevant at frequencies above several GHz. Using the data available in literature we improved our knowledge of the brightness of the unresolved extragalactic radio sources. The results obtained have general validity and they can be used to disentangle the various contributions of the sky brightness and to evaluate the CMB temperature.