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A low-frequency study of linear polarization in radio galaxies
- Source :
- Monthly Notices of the Royal Astronomical Society. 502:273-292
- Publication Year :
- 2020
- Publisher :
- Oxford University Press (OUP), 2020.
-
Abstract
- Radio galaxies are linearly polarized -- an important property that allows us to infer the properties of the magnetic field of the source and its environment. However at low frequencies, Faraday rotation substantially depolarizes the emission, meaning that comparatively few polarized radio galaxies are known at low frequencies. Using the LOFAR Two Metre Sky Survey at 150 MHz and at 20 arcsec resolution, we select 342 radio galaxies brighter than 50 mJy and larger than 100 arcsec in angular size, of which 67 are polarized (18 per cent detection fraction). These are predominantly Fanaroff Riley type II (FR-II) sources. The detection fraction increases with total flux density, and exceeds 50 per cent for sources brighter than 1 Jy. We compare the sources in our sample detected by LOFAR to those also detected in NVSS at 1400 MHz, and find that our selection bias toward bright radio galaxies drives a tendency for sources depolarized between 1400 and 150 MHz to have flatter spectra over that frequency range than those that remain polarized at 150 MHz. By comparing observed rotation measures with an analytic model we find that we are preferentially sensitive to sources in low mass environments. We also infer that sources with one polarized hotspot are inclined by a small angle to the line of sight, while sources with hotspots in both lobes lie in the plane of the sky. We conclude that low frequency polarization in radio galaxies is related to a combination of environment, flux density and jet orientation.<br />20 pages, 19 figures. Accepted for publication in MNRAS, December 22nd 2020
- Subjects :
- Physics
Line-of-sight
010308 nuclear & particles physics
Linear polarization
Radio galaxy
Astrophysics::High Energy Astrophysical Phenomena
FOS: Physical sciences
Astronomy and Astrophysics
Astrophysics::Cosmology and Extragalactic Astrophysics
LOFAR
Astrophysics
Low frequency
Polarization (waves)
Astrophysics - Astrophysics of Galaxies
01 natural sciences
symbols.namesake
Space and Planetary Science
Angular diameter
Astrophysics of Galaxies (astro-ph.GA)
0103 physical sciences
Faraday effect
symbols
010303 astronomy & astrophysics
Astrophysics::Galaxy Astrophysics
Subjects
Details
- ISSN :
- 13652966 and 00358711
- Volume :
- 502
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi.dedup.....ecb3ddd910ad4b0c6a1eb25bdc94e07a