A view of the sub-mJy populations, modelling and perspectives for future deep surveys

TL;DR

This study analyzes faint radio sources below 1 mJy using multi-wavelength data, revealing that active galactic nuclei dominate and identifying a new class of compact, low-luminosity AGN sources with unique spectral properties.

Contribution

The paper presents the first detailed optical and radio analysis of sub-mJy radio sources, highlighting the dominance of AGNs and introducing a new class of compact, flat-spectrum sources with low radio-to-optical ratios.

Findings

AGNs constitute 78% of the sub-mJy radio sources.

Discovery of a class of compact, flat/inverted-spectrum sources with low radio-to-optical ratios.

Development of radio source models for both AGN and star-forming populations.

Abstract

We use deep multi-colour (UBVRIJK) images mostly taken in the framework of the ESO Deep Public Survey (DPS) to optically identify and derive photometric redshifts for a complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5 GHz as part of the ATESP radio survey. The availability of multi-wavelength radio and optical information is exploited to infer the physical properties of the faint radio population. In particular we find that, considering both early-type galaxies and quasars as sources with an active nucleus, AGNs largely dominate our sample sub-mJy sample (78%). Further radio/optical analysis of such AGN component has revealed a somewhat unexpected class of flat/inverted-spectrum sources with low radio-to-optical ratios (R<100), which are preferentially identified with early-type galaxies. Such sources are quite compact (d<10-30 kpc), suggesting core-dominated radio emission triggered by low luminosity AGNs. This intriguing class of objects deserves further analysis, and new higher resolution radio observations are currently under way. In parallel we are developing radio source models, for both the AGN and the star-forming components of the sub-mJy radio pupulation. Here we discuss the first results.