A hidden active galactic nucleus population: the first radio luminosity functions constructed by physical process
ABSTRACT Both star formation (SF) and active galactic nuclei (AGNs) play an important role in galaxy evolution. Statistically quantifying their relative importance can be done using radio luminosity functions (RLFs). Until now these relied on galaxy classifications, where sources with a mixture of radio emission from SF and AGN are labelled as either a star-forming galaxy or an AGN. This can cause the misestimation of the relevance of AGN. Brightness temperature measurements at 144 MHz with the International LOw Frequency ARray telescope can separate radio emission from AGN and SF. We use the combination of sub-arcsec and arcsec resolution imaging of 7497 sources in the Lockman Hole and ELAIS-N1 fields to identify AGN components in the sub-arcsec resolution images and subtract them from the total flux density, leaving flux density from SF only. We construct, for the first time, RLFs by physical process, either SF or AGN activity, revealing a hidden AGN population at $L_{\textrm {144 MHz}}$$\lt 10^{24}$ W Hz$^{-1}$. This population is 1.56 $\pm$ 0.06 more than expected for $0.5\lt z\lt 2.0$ when comparing to RLFs by galaxy classification. The star-forming population has only 0.90 $\pm$ 0.02 of the expected SF. These ‘hidden’ AGNs can have significant implications for the cosmic SF rate and kinetic luminosity densities.
Authors
- L. K. Morabito (ORCID: https://orcid.org/0000-0003-0487-6651)
- J. M. G. H. J. de Jong (ORCID: https://orcid.org/0000-0001-6876-8719)
- H. J. A. Röttgering (ORCID: https://orcid.org/0000-0001-8887-2257)
- R. Kondapally (ORCID: https://orcid.org/0000-0001-6127-8151)
- I. Prandoni (ORCID: https://orcid.org/0000-0001-9680-7092)
- Dominik J. Schwarz (ORCID: https://orcid.org/0000-0003-2413-0881)
- M. Bondi (ORCID: https://orcid.org/0000-0002-9553-7999)
- P. N. Best (ORCID: https://orcid.org/0000-0001-5081-4801)
- B. H. Yue (ORCID: https://orcid.org/0009-0009-8935-2929)
- D. J. B. Smith (ORCID: https://orcid.org/0000-0001-9708-253X)
- R. J. van Weeren (ORCID: https://orcid.org/0000-0002-0587-1660)
- Frits Sweijen (ORCID: https://orcid.org/0000-0002-6470-7967)
- T. W. Shimwell (ORCID: https://orcid.org/0000-0001-5648-9069)
Institutions
- Leiden University (NL)
- University of Hertfordshire (GB)
- Durham University (GB)
- Bielefeld University (DE)
- Royal Observatory (GB)
- Istituto di Radioastronomia di Bologna (IT)
- Netherlands Institute for Radio Astronomy (NL)
- University of Edinburgh (GB)
Publication Details
- Journal
- Monthly Notices of the Royal Astronomical Society Letters
- Published
- 2024-11-04
- DOI
- https://doi.org/10.1093/mnrasl/slae104
- Citations
- 12
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 3.98
Funders
- UK Research and Innovation
- Science Foundation Ireland
- Bundesministerium für Bildung und Forschung
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek
- Max-Planck-Gesellschaft
- Centre National de la Recherche Scientifique
- Istituto Nazionale di Astrofisica
- Université d'Orléans
- Ministerium für Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen
- Observatoire de Paris, Université de Recherche Paris Sciences et Lettres
- Science and Technology Facilities Council