# A census of radio-selected AGN on the COSMOS field and of their FIR properties

**Authors:** Manuela Magliocchetti, Paola Popesso, Marcella Brusa, Mara Salvato  
**arXiv:** [1709.07230](https://arxiv.org/abs/1709.07230)  
**Date:** 2017-09-21  
**Summary page:** https://www.summarizepaper.com/en/paper/1709.07230v1/

## Key points

- Magliocchetti et al. (2017) conduct a comprehensive census of VLA-COSMOS radio sources using the new catalogue by Laigle et al. (2016)
- They successfully identify 90% of the sources and classify them into active galactic nuclei (AGN) and star-forming galaxies based on radio luminosity
- The AGN sample is complete in terms of radio selection for redshifts below z<3.5
- Out of the 704 identified AGN, 272 have corresponding counterparts in Herschel maps
- More powerful AGN are more likely to exhibit far-infrared (FIR) emission at earlier epochs due to star-forming processes within their host galaxies
- Distinction between FIR-emitting AGN and non-FIR emitters becomes apparent only at lower redshifts (z<1)
- Mid-infrared (MIR) emission is associated with ongoing star formation and smaller, younger, and more radio luminous sources
- X-ray emitters tend to appear in more massive and older galaxies
- Proposed evolutionary track suggests MIR emission in initial phase, followed by sole activity at radio wavelengths and potentially in the X-ray regime

## Summary

In their study, Magliocchetti et al. (2017) utilize the new catalogue by Laigle et al. (2016) to conduct a comprehensive census of VLA-COSMOS radio sources. They successfully identify 90% of these sources and further classify them into two categories: active galactic nuclei (AGN) and star-forming galaxies based on their radio luminosity. The authors find that the AGN sample is complete in terms of radio selection for all redshifts below z<3.5. Out of the 704 AGN identified, 272 have corresponding counterparts in the Herschel maps. By leveraging the improved statistics provided by this new sample, Magliocchetti et al. confirm previous findings that suggest that the likelihood of detecting a radio-selected AGN at far-infrared (FIR) wavelengths depends on both its radio luminosity and redshift; more powerful sources are more likely to exhibit FIR emission at earlier epochs due to star-forming processes occurring within their host galaxies. Interestingly, the distinction between FIR-emitting AGN and non-FIR emitters only becomes apparent in the lower redshift universe (z<1). At higher redshifts, these two populations become indistinguishable from each other since there is no discernible difference between FIR-emitting AGN and star-forming galaxies. The authors also focus on radio AGN that display emission at other wavelengths. They discover that mid-infrared (MIR) emission is primarily associated with ongoing star formation and with sources that are smaller, younger, and more radio luminous compared to the average parent population. On the other hand, X-ray emitters tend to preferentially appear in more massive and older galaxies. Based on their observations, Magliocchetti et al propose an evolutionary track for radio-active AGN and their host galaxies; they suggest that the initial phase of a radio active AGN and its host galaxy is characterized by MIR emission while in later stages it becomes solely active at radio wavelengths as well as potentially in the X-ray regime. This evolutionary sequence highlights the interplay between different emission processes and provides valuable insights into the formation and evolution of AGN–host galaxy systems.