Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 515, Issue 4, Pages 5758-5774Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stac2129
Keywords
acceleration of particles; radiation mechanisms: non-thermal; galaxies: active; galaxies: jets; radio continuum: galaxies
Categories
Funding
- Medical Research Council [MR/T042842/1]
- UK STFC [ST/V000594/1]
- European Union [892117]
- INAF under the SKA/CTA PRIN 'FORECaST'
- PRIN MAIN STREAM 'SAuROS' projects
- CAS-NWO programme for radio astronomy - Netherlands Organisation for Scientific Research (NWO) [629.001.024]
- ERC [804208]
- International LOFAR Telescope (ILT) [LT10 012]
- CNRS-INSU, France
- Observatoire de Paris and Universite d'Orleans, France
- BMBF, Germany
- MIWF-NRW, Germany
- MPG, Germany
- Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland
- NWO, The Netherlands
- Science and Technology Facilities Council, UK
- Ministry of Science and Higher Education, Poland
- SURF [180169]
- Marie Curie Actions (MSCA) [892117] Funding Source: Marie Curie Actions (MSCA)
- European Research Council (ERC) [804208] Funding Source: European Research Council (ERC)
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Identifying active galactic nuclei (AGNs) using brightness temperature (T-b) measurements from radio observations allows for the study of the co-evolution of AGNs and their host galaxies, with evidence suggesting a mixture of star-formation and AGN activity.
Identifying active galactic nuclei (AGNs) and isolating their contribution to a galaxy's energy budget is crucial for studying the co-evolution of AGNs and their host galaxies. Brightness temperature (T-b) measurements from high-resolution radio observations at GHz frequencies are widely used to identify AGNs. Here, we investigate using new sub-arcsecond imaging at 144 MHz with the International LOFAR Telescope to identify AGNs using T-b in the Lockman Hole field. We use ancillary data to validate the 940 AGN identifications, finding 83 percent of sources have AGN classifications from SED fitting and/or photometric identifications, yielding 160 new AGN identifications. Considering the multiwavelength classifications, brightness temperature criteria select over half of radio-excess sources, 32 percent of sources classified as radio-quiet AGNs, and 20 percent of sources classified as star-forming galaxies. Infrared colour-colour plots and comparison with what we would expect to detect based on peak brightness in 6 arcsec LOFAR maps imply that the star-forming galaxies and sources at low flux densities have a mixture of star-formation and AGN activity. We separate the radio emission from star-formation and AGN in unresolved, T-b-identified AGNs with no significant radio excess and find the AGN comprises 0.49 +/- 0.16 of the radio luminosity. Overall, the non-radio excess AGNs show evidence for having a variety of different radio emission mechanisms, which can provide different pathways for AGNs and galaxy co-evolution. This validation of AGN identification using brightness temperature at low frequencies opens the possibility for securely selecting AGN samples where ancillary data are inadequate.
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