The AGN component in deep radio fields: Results from the First Look Survey

TL;DR

This study investigates the properties of faint radio-selected AGNs in deep fields, revealing a significant presence of both radio-loud and radio-quiet AGNs, and highlighting the importance of IR colors in their identification.

Contribution

It provides the first evidence of radio-quiet AGNs in deep radio fields and demonstrates the effectiveness of IR colors in distinguishing AGN types.

Findings

Presence of radio-loud AGNs at microJy flux levels.

Detection of radio-quiet AGNs consistent with existing models.

IR colors are effective in separating AGN-triggered sources.

Abstract

We are currently exploiting the deep radio/optical/IR information available for the extra-galactic component of the Spitzer First Look Survey (FLS) to investigate the physical properties of faint radio-selected AGNs, with the aim of studying the AGN component of sub-mJy radio fields. One of the key unresolved issues is whether, as a function of cosmic epoch, low-power AGNs are more related to efficiently accreting systems (mostly radio-quiet) or to systems with very low accretion rates (mostly radio-loud). Here we present a sample of optically identified radio-emitting AGNs extracted from the FLS. Preliminary results show that at the flux densities probed by the FLS (S(1.4 GHz)> 100 microJy) we still have a significant number of radio-loud AGNs, similarly to what found in 'brighter' sub-mJy radio samples. Very interestingly, however, we have also a clear and direct evidence of a population of radio-emitting AGNs in the FLS, whose properties are consistent with those expected from existing radio-quiet AGN modeling. Such AGNs could be recognised as such thanks to the availability of IR colors which proved to be especially useful to efficiently separate radio sources triggered by AGNs, from sources triggered by star-formation. This latter result supports the idea that radio-quiet AGNs are not necessarily radio silent, and very promisingly may indicate that the bulk of the radio-quiet AGN population could emerge from studies of deeper radio samples.