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LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1

Šnidarić, Iva; Jelić, Vibor; Mevius, Maaijke; Brentjens, Michiel; Erceg, Ana; Shimwell, Timothy W.; Piras, Sara; Horellou, Cathy; Sabater, Jose; Best, Philip N.; Bracco, Andrea; Ceraj, Lana; Haverkorn, Marijke; O’Sullivan, Shane P.; Turić, Luka; Vacca, Valentina (2023) LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1. Astronomy & Astrophysics, 674 . ISSN 0004-6361

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We present the first deep polarimetric study of Galactic synchrotron emission at low radio frequencies. Our study is based on 21 observations of the European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field using the Low-Frequency Array (LOFAR) at frequencies from 114.9 to 177.4 MHz. These data are a part of the LOFAR Two-metre Sky Survey Deep Fields Data Release 1. We used very low-resolution (4.3') Stokes QU data cubes of this release. We applied rotation measure (RM) synthesis to decompose the distribution of polarised structures in Faraday depth, and cross-correlation RM synthesis to align different observations in Faraday depth. We stacked images of about 150 h of the ELAIS-N1 observations to produce the deepest Faraday cube at low radio frequencies to date, tailored to studies of Galactic synchrotron emission and the intervening magneto-ionic interstellar medium. This Faraday cube covers ~36 deg2 of the sky and has a noise of 27 µJy PSF-1 RMSF-1 in polarised intensity. This is an improvement in noise by a factor of approximately the square root of the number of stacked data cubes (~√20), as expected, compared to the one in a single data cube based on five-to-eight-hour observations. We detect a faint component of diffuse polarised emission in the stacked cube, which was not detected previously. Additionally, we verify the reliability of the ionospheric Faraday rotation corrections estimated from the satellite-based total electron content measurements to be of ~0.05 gad m-2. We also demonstrate that diffuse polarised emission itself can be used to account for the relative ionospheric Faraday rotation corrections with respect to a reference observation.

Item Type: Article
Uncontrolled Keywords: ISM: general; ISM: structure; ISM: magnetic fields; radio continuum: ISM; techniques: interferometric; techniques: polarimetric
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Divisions: Division of Experimental Physics
Project titleProject leaderProject codeProject type
Razumijevanje zračenja na niskim radio frekvencijama: ususret novoj generaciji radio teleskopa-LowFreqCROVibor Jelić; Vernesa Smolčić; Željka Marija Bošnjak; Bruno ŠlausIP-2018-01-2889HRZZ
Depositing User: Vibor Jelić
Date Deposited: 07 Feb 2024 09:59
DOI: 10.1051/0004-6361/202245124

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