The bright end of the infrared luminosity functions and the abundance of hyperluminous infrared galaxies

¹ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
e-mail: l.wang@sron.nl
² Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
³ SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁶ National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warszawa, Poland
⁷ Aix-Marseille Univ. CNRS, CNES, LAM, Marseille, France
⁸ Astronomy Centre, Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
¹⁰ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
¹¹ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown 6140, South Africa
¹² USN, Observatoire de Paris, CNRS, PSL, UO, Nançay, France
¹³ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
¹⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
¹⁶ Department of Physics and Astronomy, University of Hawaii, 2505 Correa Road, Honolulu, HI 96822, USA
¹⁷ Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822, USA
¹⁸ CSIRO Astronomy and Space Science, PO Box 1130, Bentley WA 6102, Australia
¹⁹ Inter-University Institute for Data Intensive Astronomy, Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, 7535 Bellville, Cape Town, South Africa

Received: 1 July 2020
Accepted: 9 September 2020

Abstract

Aims. We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities >10¹³L_⊙, thanks to the combination of the high sensitivity, angular resolution, and large area of the LOFAR Deep Fields, which probes an unprecedented dynamic range of luminosity and volume.

Methods. We cross-match Herschel sources and LOFAR sources in Boötes (8.63 deg²), Lockman Hole (10.28 deg²), and ELAIS-N1 (6.74 deg²) with rms sensitivities of ~32, 22, and 20 μJy beam⁻¹, respectively. We divide the matched samples into “unique” and “multiple” categories. For the multiple matches, we de-blend the Herschel fluxes using the LOFAR positions and the 150-MHz flux densities as priors. We perform spectral energy distribution fitting, combined with multi-wavelength counterpart identifications and photometric redshift estimates, to derive IR luminosities.

Results. The depth of the LOFAR data allows us to identify highly complete (~92% completeness) samples of bright Herschel sources with a simple selection based on the 250 μm flux density (45, 40, and 35 mJy in Boötes, Lockman Hole, and ELAIS-N1, respectively). Most of the bright Herschel sources fall into the unique category (i.e. a single LOFAR counterpart). For the multiple matches, there is excellent correspondence between the radio emission and the far-IR emission. We find a good agreement in the IR LFs with a previous study out to z ~ 6 which used de-blended Herschel data. Our sample gives the strongest and cleanest indication to date that the population of HLIRGs has surface densities of ~5 to ~18/deg² (with variations due to a combination of the applied flux limit and cosmic variance) and an uncertainty of a factor of ≲2. In comparison, the GALFORM semi-analytic model significantly under-predicts the abundance of HLIRGs.