On the depolarization asymmetry seen in giant radio lobes

Bell, M. B.; Comeau, S. P.

doi:10.1007/s10509-012-1310-4

Cited by 3 publications

(2 citation statements)

References 39 publications

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“…In fact, a recent study by Bell & Comeau (2012) found, for sources exhibiting the Laing-Garrington effect, that the jet brightness asymmetry on kiloparsec scales cannot be explained by beaming and therefore must be intrinsic (in cases where the estimated kiloparsec-scale outflow speeds are close to 0.1c). They conclude that a Laing-Garrington effect due to intrinsic differences in the Faraday rotating material within radio galaxy lobes cannot be discounted.…”

Section: External Depolarization Modelmentioning

confidence: 99%

Thermal Plasma in the Giant Lobes of the Radio Galaxy Centaurus A

O’Sullivan

Feain

McClure-Griffiths

et al. 2013

ApJ

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We present a Faraday rotation measure (RM) study of the diffuse, polarized, radio emission from the giant lobes of the nearest radio galaxy, Centaurus A. After removal of the smooth Galactic foreground RM component, using an ensemble of background source RMs located outside the giant lobes, we are left with a residual RM signal associated with the giant lobes. We find that the most likely origin of this residual RM is from thermal material mixed throughout the relativistic lobe plasma. The alternative possibility of a thin-skin/boundary layer of magnetoionic material swept up by the expansion of the lobes is highly unlikely since it requires, at least, an order of magnitude enhancement of the swept-up gas over the expected intragroup density on these scales. Strong depolarization observed from 2.3 to 0.96 GHz also supports the presence of a significant amount of thermal gas within the lobes; although depolarization solely due to RM fluctuations in a foreground Faraday screen on scales smaller than the beam cannot be ruled out. Considering the internal Faraday rotation scenario, we find a thermal gas number density of ∼10 −4 cm −3 , implying a total gas mass of ∼10 10 M within the lobes. The thermal pressure associated with this gas (with temperature kT ∼ 0.5 keV, obtained from recent X-ray results) is approximately equal to the non-thermal pressure, indicating that over the volume of the lobes, there is approximate equipartition between the thermal gas, radio-emitting electrons, and magnetic field (and potentially any relativistic protons present).

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Section: External Depolarization Modelmentioning

confidence: 99%

Thermal Plasma in the Giant Lobes of the Radio Galaxy Centaurus A

O’Sullivan

Feain

McClure-Griffiths

et al. 2013

ApJ

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“…Recent observations of Centaurus A by O'Sullivan et al (2013) provide evidence of depolarisation across radio lobes from the presence of a significant amount of thermal gas within the lobes. Bell & Comeau (2013) examine a sample of radio sources exhibiting the Laing-Garrington effect and show that the depolarisation cannot be explained by beaming. Farnes et al (2014) compared total intensity spectral indices with polarised spectral indices to show that there are two populations of polarised radio sources: core-and jetdominated sources.…”

Section: Environments Of Polarised Radio Sourcesmentioning

confidence: 99%

Radio galaxies and their magnetic fields out to z ≤ 3

Banfield¹,

Schnitzeler²,

George³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We present polarisation properties at 1.4 GHz of two separate extragalactic source populations: passive quiescent galaxies and luminous quasar-like galaxies. We use data from the Wide-Field Infrared Survey Explorer data to determine the host galaxy population of the polarised extragalactic radio sources. The quiescent galaxies have higher percentage polarisation, smaller radio linear size, and 1.4 GHz luminosity of 6 × 10 21 < L 1.4 < 7 × 10 25 W Hz −1 , while the quasar-like galaxies have smaller percentage polarisation, larger radio linear size at radio wavelengths, and a 1.4 GHz luminosity of 9 × 10 23 < L 1.4 < 7 × 10 28 W Hz −1 , suggesting that the environment of the quasar-like galaxies is responsible for the lower percentage polarisation. Our results confirm previous studies that found an inverse correlation between percentage polarisation and total flux density at 1.4 GHz. We suggest that the population change between the polarised extragalactic radio sources is the origin of this inverse correlation and suggest a cosmic evolution of the space density of quiescent galaxies. Finally, we find that the extragalactic contributions to the rotation measures (RMs) of the nearby passive galaxies and the distant quasar-like galaxies are different. After accounting for the RM contributions by cosmological large-scale structure and intervening Mg II absorbers we show that the distribution of intrinsic RMs of the distant quasar-like sources is at most four times as wide as the RM distribution of the nearby quiescent galaxies, if the distribution of intrinsic RMs of the WISE-Star sources itself is at least several rad m −2 wide.

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A polarization study of jets interacting with turbulent magnetic fields

Meenakshi,

Mukherjee,

Bodo

et al. 2023

Monthly Notices of the Royal Astronomical Society

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We investigate the effect of the jet’s immediate surroundings on the non-thermal synchrotron emission and its polarization properties. The ambient medium is equipped with a turbulent magnetic field, which is compressed and amplified by the jets as they progress. This leads to high polarization at the forward shock surface. The randomness in the magnetic polarities of the external fields in the shocked ambient medium (SAM) results in vector cancellation of the polarized components from the jet, thereby causing depolarization of the radiation from the cocoon. We find that due to the slow decay of the fields in the SAM, such depolarization by the fields with large correlation lengths is more prominent when compared to the small-scale fields. Also, the low-power jets, which have magnetic fields comparable in strength to those in the SAM, are more severely affected by the SAM’s depolarizing effect, than the high-power ones. The turbulent backflows in the cocoon, as well as the shearing of fields near the contact discontinuity, strengthen the poloidal component in the jet. This causes internal depolarization due to the cancellation of the orthogonally polarized components along the line of sight as the field transitions from ordered toroidal to poloidal. The synchrotron maps display high-emission filaments in the cocoon with magnetic fields aligned along them. The kink instability leads to the wiggling motion of the jet’s spine, resulting in hotspot complexes in low-power sources.

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On the depolarization asymmetry seen in giant radio lobes

Cited by 3 publications

References 39 publications

Thermal Plasma in the Giant Lobes of the Radio Galaxy Centaurus A

Thermal Plasma in the Giant Lobes of the Radio Galaxy Centaurus A

Radio galaxies and their magnetic fields out to z ≤ 3

A polarization study of jets interacting with turbulent magnetic fields

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