A hidden Active Galactic Nuclei population: the first radio luminosity functions constructed by physical process

arXiv (Cornell University)

Abstract

Both star formation (SF) and Active Galactic Nuclei (AGN) play an important role in galaxy evolution. Statistically quantifying their relative importance can be done using radio luminosity functions. 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 LOFAR telescope can separate radio emission from AGN and SF. We use the combination of sub-arcsec and arcsec resolution imaging of 7,497 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, radio luminosity functions by physical process, either SF or AGN activity, revealing a hidden AGN population at $L_{\textrm{144MHz}}$$<10^{24}$ W$\,$Hz$^{-1}$ . This population is 1.56$\pm$0.06 more than expected for $0.5

Authors 11

1. Leah K. Morabito

   Durham University

   Affiliation as printed

   Centre for Extragalactic Astronomy , Department of Physics , Durham University , Durham DH1 3LE , UK

   Institute for Computational Cosmology , Department of Physics , Durham University , South Road , Durham DH1 3LE , UK

2. R. Kondapally

   Royal Observatory · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy , University of Edinburgh Royal Observatory , Blackford Hill , Edinburgh , EH9 3HJ , UK

3. P. N. Best

   Royal Observatory · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy , University of Edinburgh Royal Observatory , Blackford Hill , Edinburgh , EH9 3HJ , UK

4. Frits Sweijen

   Durham University

   Affiliation as printed

   Centre for Extragalactic Astronomy , Department of Physics , Durham University , Durham DH1 3LE , UK

5. M. Bondi

   Istituto di Radioastronomia di Bologna

   Affiliation as printed

   INAF -Istituto di Radioastronomia , Via Gobetti 101 , 40129 Bologna , Italy

6. Dominik J. Schwarz

   Bielefeld University

   Affiliation as printed

   Fakultät für Physik , Universität Bielefeld , Postfach 100131 , 33501 Bielefeld , Germany

7. Daniel J. B. Smith

   University of Hertfordshire

   Affiliation as printed

   Centre for Astrophysics Research , University of Hertfordshire , College Lane , Hatfield AL10 9AB , UK

8. Reinout J. van Weeren Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

9. H. J. A. Rottgering
10. T. W. Shimwell Aachen Leiden Observatory

    Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

    Affiliation as printed

    ASTRON , Netherlands Institute for Radio Astronomy , Oude Hoogeveensedijk 4 , 7991 PD , Dwingeloo , the Netherlands

    Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

11. Isabella Prandoni

    Istituto di Radioastronomia di Bologna

    Affiliation as printed

    INAF -Istituto di Radioastronomia , Via Gobetti 101 , 40129 Bologna , Italy