Volume 656, December 2021
|Number of page(s)||18|
|Published online||03 December 2021|
The LOFAR Two-metre Sky Survey Deep Fields
A new analysis of low-frequency radio luminosity as a star-formation tracer in the Lockman Hole region
INAF-Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
2 Italian ALMA Regional Centre, Via Gobetti 101, 40129 Bologna, Italy
3 INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
4 SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
5 European Southern Observatory, Karl-Schwarzchild-Strasse 2, 85748 Garching bei München, Germany
6 Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
7 Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
8 Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK
9 INAF-Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
10 Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
11 National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warszawa, Poland
12 Aix Marseille Univ. CNRS, CNES, LAM, Marseille, France
13 GEPI & USN, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
14 Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown 6140, 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
Accepted: 10 September 2021
We have exploited LOFAR deep observations of the Lockman Hole field at 150 MHz to investigate the relation between the radio luminosity of star-forming galaxies (SFGs) and their star-formation rates (SFRs), as well as its dependence on stellar mass and redshift. The adopted source classification, SFRs, and stellar masses are consensus estimates based on a combination of four different spectral energy distribution fitting methods. We note a flattening of the radio spectra of a substantial minority of sources below ∼1.4 GHz. Such sources have thus a lower ‘radio-loudness’ level at 150 MHz than expected from extrapolations from 1.4 GHz using the average spectral index. We found a weak trend towards a lower SFR/L150 MHz ratio for higher stellar mass, M⋆. We argue that such a trend may account for most of the apparent redshift evolution of the L150 MHz/SFR ratio, in line with previous work. Our data indicate a weaker evolution than found by some previous analyses. We also find a weaker evolution with redshift of the specific SFR than found by several (but not all) previous studies. Our radio selection provides a view of the distribution of galaxies in the SFR–M⋆ plane complementary to that of optical and near-IR selection. It suggests a higher uniformity of the star-formation history of galaxies than implied by some analyses of optical and near-IR data. We have derived luminosity functions at 150 MHz of both SFGs and radio-quiet (RQ) AGN at various redshifts. Our results are in very good agreement with the T-RECS simulations and with literature estimates. We also present explicit estimates of SFR functions of SFGs and RQ AGN at several redshifts derived from our radio survey data.
Key words: galaxies: star formation / galaxies: evolution
© ESO 2021
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