Multiwavelength Properties of Infrared-Faint Radio Sources Based on Spectral Energy Distribution Analysis

TL;DR

This study models the spectral energy distributions of infrared-faint radio sources to understand their dust, star formation, and AGN activity, revealing they are likely AGN-dominated low-luminosity counterparts of high-redshift radio galaxies.

Contribution

It provides the first detailed SED analysis of IFRSs, demonstrating their AGN dominance and comparing multi-component models to reveal their nature.

Findings

IFRSs are most likely AGN with significant dust heated by AGN.

The median SED resembles an AGN-starburst composite.

IR luminosities suggest IFRSs are low-luminosity high-redshift radio galaxy counterparts.

Abstract

Infrared-faint radio sources (IFRSs) are believed to be a rare class of radio-loud active galactic nuclei (RL AGN) characterized by their high radio-to-infrared flux density ratios of up to several thousands. Previous studies have shown that a fraction of IFRSs are likely to be hosted in dust-obscured galaxies (DOGs). In this paper, our aim was to probe the dust properties, star formation rate (SFR), and AGN activity of IFRSs by modeling the UV-to-infrared spectral energy distribution (SED) of 20 IFRSs with spectroscopic redshifts ranging from 1.2 to 3.7. We compare the Bayesian evidence of a three-component model (stellar, AGN and cold dust) with that of a two-component model (stellar and cold dust) for six IFRSs in our sample with far-infrared (FIR) photometry and find that the three-component model has significantly higher Bayesian evidence, suggesting that IFRSs are most likely to be AGN. The median SED of our IFRS sample shows similarities to AGN-starburst composite in the IR regime. The derived IR luminosities of IFRSs indicate that they are low-luminosity counterparts of high-redshift radio galaxies. We disentangle the contributions of AGN-heated and star-formation-heated dust to the IR luminosity of IFRSs and find that our sample is likely AGN-dominated. However, despite the evidence for significant impact of AGN on the host galaxy, the AGN luminosity of our sample does not show correlation with the SFR of the sources.