LOFAR Deep Fields: probing a broader population of polarized radio galaxies in ELAIS-N1

¹ Faculty of Physics and Astronomy, Astronomical Institute, Ruhr University Bochum, Universitätstrasse 150, 44801 Bochum, Germany
e-mail: herrera@astro.rub.de
² School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, D09 W6Y4, Ireland
³ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
⁴ Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
⁵ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
⁶ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁷ SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁸ CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia
⁹ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA 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 Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹⁴ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁵ INAF-IRA, Via P. Gobetti 101, 40129 Bologna, Italy

Received: 11 July 2020
Accepted: 22 August 2020

Abstract

We present deep polarimetric observations of the European Large Area ISO Survey-North 1 (ELAIS-N1) field using the Low Frequency Array (LOFAR) at 114.9–177.4 MHz. The ELAIS-N1 field is part of the LOFAR Two-metre Sky Survey deep fields data release I. For six eight-hour observing epochs, we align the polarization angles and stack the 20″-resolution Stokes Q, U-parameter data cubes. This produces a 16 deg² image with 1σ_QU sensitivity of 26 μJy beam⁻¹ in the central area. In this paper, we demonstrate the feasibility of the stacking technique, and we generate a catalog of polarized sources in ELAIS-N1 and their associated Faraday rotation measures (RMs). While in a single-epoch observation we detect three polarized sources, this number increases by a factor of about three when we consider the stacked data, with a total of ten sources. This yields a surface density of polarized sources of one per 1.6 deg². The Stokes I images of three of the ten detected polarized sources have morphologies resembling those of FR I radio galaxies. This represents a greater fraction of this type of source than previously found, which suggests that more sensitive observations may help with their detection.