The LOFAR two metre sky survey data release 2: probabilistic spectral source classifications and faint radio source demographics

Monthly Notices of the Royal Astronomical Society, vol. 534, pp. 1107–1126

Abstract

ABSTRACT We present an analysis of 152 355 radio sources identified in the second data release of the LOFAR Two Metre Sky Survey (LoTSS-DR2) with Sloan Digital Sky Survey (SDSS) spectroscopic redshifts in the range $0.00 \lt z \lt 0.57$. Using Monte Carlo simulations, we determine the reliability of each source exhibiting an excess in radio luminosity relative to that predicted from their H $\alpha$ emission, and, for a subset of 124 023 sources we combine this measurement with a full BPT analysis. Using these two independent diagnostics, we determine the reliability of each source hosting a supermassive black hole of high or low Eddington-scaled accretion rate, and combine the measurements to determine the reliability of sources belonging to each of four physical classes of objects: star-forming galaxies (SFGs), radio-quiet active galactic nuclei (RQAGN), and high- or low-excitation radio galaxies (HERGs or emission-line LERGs). The result is a catalogue that enables user-defined samples of radio sources with a reliability threshold suited to their science goal, for example prioritizing purity or completeness. Here, we select high-confidence samples of radio sources (>90 per cent reliability) to report: 38 588 radio-excess AGNs in the LoTSS-DR2 sample (362 HERGs, and 12 648 emission-line LERGs), together with 38 729 SFGs, and 18 726 RQAGN. We validate these results through comparison to literature using independent emission-line measurements, and to widely adopted WISE photometric selection techniques. While our use of SDSS spectroscopy limits our current analysis to $\sim 4$ per cent of the LoTSS-DR2 catalogue, our method is directly applicable to data from the forthcoming WEAVE-LOFAR survey, which will obtain over a million spectra of 144 MHz selected sources.

Authors 11

1. Alyssa B. Drake corresponding

   University of Hertfordshire

   Affiliation as printed

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

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

2. Daniel J. B. Smith

   University of Hertfordshire

   Affiliation as printed

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

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

3. M. J. Hardcastle

   University of Hertfordshire

   Affiliation as printed

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

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

4. P. N. Best

   Royal Observatory · University of Edinburgh

   Affiliation as printed

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

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

5. R. Kondapally

   Royal Observatory · University of Edinburgh

   Affiliation as printed

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

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

6. M I Arnaudova

   University of Hertfordshire

   Affiliation as printed

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

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

7. Soumyadeep Das

   University of Hertfordshire

   Affiliation as printed

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

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

8. Shravya Shenoy

   University of Hertfordshire

   Affiliation as printed

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

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

9. K. J. Duncan

   Royal Observatory · University of Edinburgh

   Affiliation as printed

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

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

10. Huub J. A. Röttgering Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University , NL-2300 RA Leiden ,

    Leiden Observatory, Leiden University, NL-2300 RA Leiden, Netherlands

11. Cyril Tasse

    Centre National de la Recherche Scientifique · Rhodes University · Université Paris Sciences et Lettres · Observatoire de Paris · Galaxies, Etoiles, Physique et Instrumentation

    Affiliation as printed

    Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University , Grahamstown 6140 ,

    GEPI & ORN, Observatoire de Paris, Université PSL, CNRS , 5 Place Jules Janssen, F-92190 Meudon ,

    Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown, 6140, South Africa