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

Journal article, 2025

Infrared-faint radio sources (IFRSs) are believed to be a rare class of radio-loud active galactic nuclei (AGNs) characterized by their high radio-to-infrared flux density ratios of up to several thousand. Previous studies have shown that a fraction of IFRSs are likely to be hosted in dust-obscured galaxies. In this paper, our aim is 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 photometry and find that the three-component model has significantly higher Bayesian evidence, suggesting that IFRSs are most likely to be AGNs. The median SED of our IFRS sample shows similarities to an 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 an AGN on the host galaxy, the AGN luminosity of our sample does not show correlation with the SFR of the sources.