We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array ( MWA ) , covering 625 deg ^ { 2 } centered on \alpha = 0 \mbox { $ { } ^ { \mathrm { h } } $ } , \delta = -27 \arcdeg .
The sensitivity available in our deep observations allows \edit 1an in-band , frequency-dependent analysis of polarized structure for the first time at long wavelengths .
Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component .
At these wavelengths , the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure .
The observations are sensitive to diffuse polarized emission at \sim 54 \arcmin resolution with a sensitivity of 5.9 mJy beam ^ { -1 } and compact polarized sources at \sim 2.4 \arcmin resolution with a sensitivity of 2.3 mJy beam ^ { -1 } for a subset ( 400 deg ^ { 2 } ) of this field .
The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background .
Our observations reveal large-scale structures ( \sim 1 \arcdeg – 8 \arcdeg in extent ) in linear polarization clearly detectable in \sim 2 minute snapshots , which would remain undetectable by interferometers with minimum baseline lengths > 110 m at 154 MHz .
The brightness temperature of these structures is on average 4 K in polarized intensity , peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from -2 rad m ^ { -2 } to 10 rad m ^ { -2 } with a large fraction peaking at \sim + 1 rad m ^ { -2 } .
We estimate a distance of 51 \pm 20 pc to the polarized emission based on measurements of the in-field pulsar J2330 - 2005 .
We detect four extragalactic linearly polarized point sources within the field in our compact source survey .
Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz , we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz .