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

TL;DR

This study uses LOFAR deep polarimetric observations and stacking techniques to detect and catalog polarized radio galaxies in the ELAIS-N1 field, revealing a higher fraction of FR I morphologies than previously observed.

Contribution

It introduces a stacking method for deep polarization imaging with LOFAR, increasing the detection of polarized sources and their Faraday RMs in the ELAIS-N1 field.

Findings

Detected 10 polarized sources with stacking, tripling single-epoch detections.

Found a higher fraction of FR I-like morphologies among polarized sources.

Achieved a 1σ QU sensitivity of 26 μJy/beam in the deep field.

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 deg$^2$ image with 1$\sigma_{\rm QU}$ sensitivity of 26 $\mu$Jy/beam 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 deg$^2$. 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.