The Contribution of Radio Selected Star Forming Galaxies to the IR Energy Density Budget

TL;DR

This study evaluates methods to distinguish star-forming galaxies from AGN in faint radio surveys and assesses their contribution to the infrared energy density, highlighting future survey capabilities and galaxy evolution trends.

Contribution

It compares current and future multi-wavelength methods for classifying radio sources and analyzes the evolution of galaxy luminosity contributions up to redshift 2.5.

Findings

Mid-IR to radio and near-IR to radio flux ratios are highly effective for classification.

Future radio surveys will enhance morphological and spectral index discrimination.

The fraction of LIRGs remains constant or decreases above z=1, while ULIRGs increase up to z=2.5.

Abstract

We have used several different methods (radio morphology, radio spectral index, mid-IR to radio and near-IR to radio flux density ratios) to discriminate between AGN and SFGs in faint, sub-mJy radio surveys. We find that the latter two methods are the most powerful with current multi-wavelength data, but that future radio surveys with eMERLIN, LOFAR etc. (and ultimately the SKA) will greatly increase the power of the morphology and spectral index methods. As an example of the science possible we derive the IR luminosity density from the radio-selected SFGs using the radio/IR luminosity correlation. We also examine the contribution by luminosity to the total IR luminosity density and find evidence that fraction of LIRGs remains constant or decreases above z=1 while the relative fraction of ULIRGs continues to increase up to z=2.5.