The LOFAR Two-metre Sky Survey Deep Fields

The star-formation rate–radio luminosity relation at low frequencies

¹ Centre for Astrophysics Research, University of Hertfordshire, Hatfield, AL10 9AB, UK
e-mail: d.j.b.smith@herts.ac.uk
² CSIRO Astronomy and Space Science, PO Box 1130, Bentley WA 6102, Australia
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 Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
⁶ Astronomy Centre, Department of Physics & Astronomy, University of Sussex, Brighton, BN1 9QH, UK
⁷ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁸ GEPI & USN, Observatoire de Paris, Université PSL, CNRS, 5 place Jules Jannsen, 92190 Meudon, France
⁹ Department of Physics & Electronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
¹⁰ INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
¹¹ Italian ALMA Regional Centre, Via Gobetti 101, 40129 Bologna, Italy
¹² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ Astrophysics, Department of Physics, Keble Road, Oxford, OX1 3RH, UK
¹⁴ Department of Physics & Astronomy, University of the Western Cape, Private Bag X17, Bellville, Cape Town 7535, South Africa
¹⁵ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
¹⁶ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands

Received: 4 September 2020
Accepted: 12 November 2020

Abstract

In this paper, we investigate the relationship between 150 MHz luminosity and the star-formation rate – the SFR-L_{150 MHz} relation – using 150 MHz measurements for a near-infrared selected sample of 118 517 z < 1 galaxies. New radio survey data offer compelling advantages over previous generation surveys for studying star formation in galaxies, including huge increases in sensitivity, survey speed, and resolution, while remaining impervious to extinction. The LOFAR Surveys Key Science Project is transforming our understanding of the low-frequency radio sky, with the 150 MHz data over the European Large Area Infrared Space Observatory Survey-North 1 field reaching an rms sensitivity of 20 μJy beam⁻¹ over 10 deg² at 6 arcsec resolution. All of the galaxies studied have SFR and stellar mass estimates that were derived from energy balance spectral energy distribution fitting using redshifts and aperture-matched forced photometry from the LOFAR Two-metre Sky Survey (LoTSS) Deep Fields data release. The impact of active galactic nuclei (AGN) is minimised by leveraging the deep ancillary data in the LoTSS data release, alongside median-likelihood methods that we demonstrate are resistant to AGN contamination. We find a linear and non-evolving SFR-L_{150 MHz} relation, apparently consistent with expectations based on calorimetric arguments, down to the lowest SFRs < 0.01M_⊙ yr⁻¹. However, we also recover compelling evidence for stellar mass dependence in line with previous work on this topic, in the sense that higher mass galaxies have a larger 150 MHz luminosity at a given SFR, suggesting that the overall agreement with calorimetric arguments may be a coincidence. We conclude that, in the absence of AGN, 150 MHz observations can be used to measure accurate galaxy SFRs out to z = 1 at least, but it is necessary to account for stellar mass in the estimation in order to obtain 150 MHz-derived SFRs accurate to better than 0.5 dex. Our best-fit relation is log₁₀(L_{150 MHz} ∕W Hz⁻¹) = (0.90 ± 0.01)log₁₀(ψ∕M_⊙ yr⁻¹) + (0.33 ± 0.04)log₁₀(M∕10¹⁰M_⊙) + 22.22 ± 0.02.