A model for the cosmological evolution of low frequency radio sources

TL;DR

This paper introduces a new evolutionary model for low-frequency radio sources (<5 GHz) that accounts for luminosity evolution, source counts, and redshift distributions, with implications for large-scale structure and the ISW effect.

Contribution

The paper presents a novel model extending existing high-frequency models to lower frequencies, incorporating luminosity-dependent decline and better explaining observational data.

Findings

Luminosity evolution fits local luminosity functions and source counts.

High-redshift decline in source luminosities supports 'downsizing' in radio sources.

Enhanced significance in ISW effect detection using new CMB analysis.

Abstract

We present a new evolutionary model that describes the population properties of radio sources at frequencies <5 GHz, thus complementing the De Zotti et al. (2005) model, holding at higher frequencies. We find that simple analytic luminosity evolution is still sufficient to fit the wealth of available data on local luminosity functions, multi-frequency source counts, and redshift distributions. However, the fit requires a luminosity-dependent decline of source luminosities at high redshifts, at least for steep-spectrum sources, thus confirming earlier indications of a "downsizing" also for radio sources. The upturn of source counts at sub-mJy levels is accounted for by a straightforward extrapolation, using the empirical far-IR/radio correlation, of evolutionary models matching the far-IR counts and redshift distributions of star-forming galaxies. We also discuss the implications of the new model for the interpretation of data on large-scale clustering of radio sources and on the Integrated Sachs-Wolfe (ISW) effect, and for the investigation of the contribution of discrete sources to the extragalactic background. As for the ISW effect, a new analysis exploiting a very clean CMB map, yields at a substantially higher significance than reported before.