The intergalactic magnetic field probed by a giant radio galaxy

O’Sullivan, S. P.; Machalski, J.; Eck, Cameron L. Van; Heald, G.; Brüggen, M.; Fynbo, J. P. U.; Heintz, K. E.; Lara-López, M. A.; Vacca, V.; Hardcastle, M. J.; Shimwell, T. W.; Tasse, C.; Vazza, Franco; Andernach, H.; Birkinshaw, Mark; Haverkorn, M.; Horellou, C.; Williams, W. L.; Harwood, J. J.; Brunetti, G.; Anderson, J. M.; Mao, Sui Ann; Nikiel-Wroczyński, B.; Takahashi, Keitaro; Carretti, E.; Vernstrom, Tessa; Weeren, R. J. van; Orrù, E.; Morabito, L. K.; Callingham, J. R.

doi:10.1051/0004-6361/201833832

Cited by 65 publications

(58 citation statements)

References 128 publications

(152 reference statements)

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“…The difference in the ∆RM signal rms values between physical and random pairs is only ∼ 10 rad m −2 , less than the average pair uncertainties. The difference reported for the lobes of a 3.4-Mpc giant radio galaxy by O'Sullivan et al (2019) (attributed to the IGM) had an uncertainty of ±0.1 rad m −2 . That was using data from the LOFAR telescope, where at low frequencies (∼ 150 MHz) the resolution in Faraday space is approximately 1 rad m −2 .…”

Section: Uncertainties and Selection Effectsmentioning

confidence: 94%

Differences in Faraday Rotation between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields

Vernstrom

Gaensler

Rudnick

et al. 2019

ApJ

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112

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Faraday rotation measures (RMs) of extragalactic radio sources provide information on line-of-sight magnetic fields, including contributions from our Galaxy, source environments, and the intergalactic medium (IGM). Looking at differences in RMs, ∆RM, between adjacent sources on the sky can help isolate these different components. In this work, we classify adjacent polarized sources in the NVSS as random or physical pairs. We recompute and correct the uncertainties in the NVSS RM catalog, since these were significantly overestimated. Our sample contains 317 physical and 5111 random pairs, all with Galactic latitudes |b| ≥ 20 • , polarization fractions ≥ 2%, and angular separations between 1.5 and 20 . We find an rms ∆RM of 14.9 ± 0.4 rad m −2 and 4.6 ± 1.1 rad m −2 for random and physical pairs, respectively. This means polarized extragalactic sources that are close on the sky, but at different redshifts, have larger differences in RM than two components of one source. This difference of ∼ 10 rad m −2 is significant at 5σ, and persists in different data subsamples. While there have been other statistical studies of ∆RM between adjacent polarized sources, this is the first unambiguous demonstration that some of this RM difference must be extragalactic, thereby providing a firm upper limit on the RM contribution of the IGM. If the ∆RMs originate local to the sources, then the local magnetic field difference between random sources is a factor of two larger than between components of one source. Alternatively, attributing the difference in ∆RMs to the intervening IGM yields an upper limit on the IGM magnetic field strength of 40 nG.

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Section: Uncertainties and Selection Effectsmentioning

confidence: 94%

Differences in Faraday Rotation between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields

Vernstrom

Gaensler

Rudnick

et al. 2019

ApJ

Self Cite

112

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“…• A lack of detectable polarization for high surface brightness objects gives evidence for substantial depolarization -a combination of factors such as the finite telescope beam, inhomogeneous magnetic field structures in the lobes or in their surrounding environment and Faraday rotation will reduce the observed polarization (as described below). Measurements of depolarization in the lobes can, in principle, trace their magnetoionic properties and their ther-mal particle content, or that of their environment (Dreher et al 1987;O'Sullivan et al 2017O'Sullivan et al , 2019Knuettel et al 2019).…”

Section: Polarized Emission Of Radio-loud Agnmentioning

confidence: 99%

A low-frequency study of linear polarization in radio galaxies

Mahatma

Hardcastle

Harwood

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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 a resolution of 20 arcsec, 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 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 the LOw Frequency ARray (LOFAR) to those also detected in NRAO VLA Sky Survey at 1400 MHz, and find that our selection bias towards 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.

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“…Indeed, in recent years, the low-frequency polarised sky has been explored in greater detail than ever before, with detections of large-scale diffuse Galactic foreground along many lines of sight (LOSs) (e.g., Jelić et al 2015;Lenc et al 2016;Van Eck et al 2017 as well as many surveys that have begun to study the polarised extragalactic source population (e.g., Bernardi et al 2013;Mulcahy et al 2014;Van Eck et al 2017;Lenc et al 2018;Neld et al 2018;O'Sullivan et al 2019O'Sullivan et al , 2020Stuardi et al 2020;Cantwell et al 2020).…”

Section: Introductionmentioning

confidence: 99%

The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths

Riseley

Galvin

Sobey

et al. 2020

Publ. Astron. Soc. Aust.

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The low-frequency linearly polarised radio source population is largely unexplored. However, a renaissance in low-frequency polarimetry has been enabled by pathfinder and precursor instruments for the Square Kilometre Array. In this second paper from the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey, or POGS-we present the results from our all-sky MWA Phase I Faraday Rotation Measure survey. Our survey covers nearly the entire Southern sky in the Declination range $-82^\circ$ to $+30^\circ$ at a resolution between around three and seven arcminutes (depending on Declination) using data in the frequency range 169−231 MHz. We have performed two targeted searches: the first covering 25 489 square degrees of sky, searching for extragalactic polarised sources; the second covering the entire sky South of Declination $+30^\circ$ , searching for known pulsars. We detect a total of 517 sources with 200 MHz linearly polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are known radio pulsars. All sources in our catalogues have Faraday rotation measures in the range $-328.07$ to $+279.62$ rad m−2. The Faraday rotation measures are broadly consistent with results from higher-frequency surveys, but with typically more than an order of magnitude improvement in the precision, highlighting the power of low-frequency polarisation surveys to accurately study Galactic and extragalactic magnetic fields. We discuss the properties of our extragalactic and known-pulsar source population, how the sky distribution relates to Galactic features, and identify a handful of new pulsar candidates among our nominally extragalactic source population.

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The intergalactic magnetic field probed by a giant radio galaxy

Cited by 65 publications

References 128 publications

Differences in Faraday Rotation between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields

Differences in Faraday Rotation between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields

A low-frequency study of linear polarization in radio galaxies

The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths

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