Polarized point sources in the LOFAR Two-meter Sky Survey: A preliminary catalog
Review article, 2018

The polarization properties of radio sources at very low frequencies (<200 MHz) have not been widely measured, but the new generation of low-frequency radio telescopes, including the Low Frequency Array (LOFAR: a Square Kilometre Array Low pathfinder), now gives us the opportunity to investigate these properties. In this paper, we report on the preliminary development of a data reduction pipeline to carry out polarization processing and Faraday tomography for data from the LOFAR Two-meter Sky Survey (LOTSS) and present the results of this pipeline from the LOTSS preliminary data release region (10h45m–15h30m right ascension, 45°–57° declination, 570 square degrees). We have produced a catalog of 92 polarized radio sources at 150 MHz at 4.′3 resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. We estimate a lower limit to the polarized source surface density at 150 MHz, with our resolution and sensitivity, of 1 source per 6.2 square degrees. We find that our Faraday depth measurements are in agreement with previous measurements and have significantly smaller errors. Most of our sources show significant depolarization compared to 1.4 GHz, but there is a small population of sources with low depolarization indicating that their polarized emission is highly localized in Faraday depth. We predict that an extension of this work to the full LOTSS data would detect at least 3400 polarized sources using the same methods, and probably considerably more with improved data processing.


ISM: magnetic fields


C.L. Van Eck

Radboud University

M. Haverkorn

Radboud University

M.I.R. Alves

Radboud University

R. Beck

Max Planck Society

P.N. Best

University of Edinburgh

E. Carretti

INAF Osservatorio Astronomico di Cagliari

K. Chyzy

Jagiellonian University in Kraków

J.S. Farnes

Radboud University

K. Ferriere

University of Toulouse

M. J. Hardcastle

University of Hertfordshire

G. Heald

CSIRO Astronomy and Space Science

University of Groningen

Cathy Horellou

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

M. Iacobelli

Netherlands Institute for Radio Astronomy (ASTRON)

V. Jelic

Ruđer Bošković Institute

D.D. Mulcahy

University of Manchester

S. O'Sullivan

Universität Hamburg

I.M. Polderman

Radboud University

Wolfgang Reich

Max Planck Society

C. J. Riseley

CSIRO Astronomy and Space Science

H.J.A. Rottgering

Leiden University

D.H.F.M. Schnitzeler

Max Planck Society

T. W. Shimwell

Netherlands Institute for Radio Astronomy (ASTRON)

Leiden University

V. Vacca

INAF Osservatorio Astronomico di Cagliari

J. Vink

University of Amsterdam

G. J. White

Open University


Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 613 A58

Subject Categories

Subatomic Physics

Astronomy, Astrophysics and Cosmology

Other Physics Topics


Basic sciences



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