Exploring the intergalactic magnetic field by means of Faraday tomography

Akahori, Takuya; Kumazaki, Kohei; Takahashi, Keitaro; Ryu, Dongsu

doi:10.1093/pasj/psu033

Cited by 39 publications

(45 citation statements)

References 68 publications

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“…Magnetic fields in the intergalactic medium can be produced by jets from AGN, galactic winds and the motion of gases in the intergalactic medium. On the scale of the large-scale structure of the universe, magnetic fields may exist in filaments, similar to those seen in dark matter simulations [2].…”

Section: Introductionsupporting

confidence: 56%

Detecting the Magnetic Cosmic Web through Deep Radio Polarization Imaging

Hunt¹,

Taylor²,

Heyden³

2018

Proceedings of MeerKAT Science: On the Pathway to the SKA — PoS(MeerKAT2016)

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Magnetic fields are present throughout the Universe and many astrophysical processes are influenced by their presence. One of the largely unknown aspects of cosmic magnetism is that of the cosmic web and how magnetic fields behave in large scale structure. Due to the indirect nature of the detection of these fields, it is difficult to determine much about the origin and evolution of magnetic fields. One method of detection is to measure how the polarisation angle of light is rotated in the presence of electrons and a magnetic field. In this paper, we simulate the Rotation Measure (RM) experienced by radio emission as it travels from an extragalactic source to the observer in large-scale simulations. Our aim is to investigate the effect of extragalactic magnetic fields on the spatial distribution of RM. This paper aims to produce RM maps of the simulated universe and use these to inform upcoming radio surveys and how we can use observations to investigate the cosmic web.

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Section: Introductionsupporting

confidence: 56%

Detecting the Magnetic Cosmic Web through Deep Radio Polarization Imaging

Hunt¹,

Taylor²,

Heyden³

2018

Proceedings of MeerKAT Science: On the Pathway to the SKA — PoS(MeerKAT2016)

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“…The modern techniques of analysis, such as model fitting of the fractional polarization components q and u (e.g., Farnsworth et al 2011;Ideguchi et al 2014), rotation measure synthesis (e.g., Brentjens & de Bruyn 2005;Akahori et al 2014b) and Faraday synthesis (Bell & Enßlin 2012), and the future radio surveys will partially overcome this problem. The large bandwidth of the new radio interferometers will allow us to reduce the risk of nπ-ambiguity, which is particularly strong when the λ 2 -fit approach is used, as well as to reach a sufficiently high resolution in Faraday depth to distinguish nearby Faraday components.…”

Section: Discussionmentioning

confidence: 99%

Using rotation measure grids to detect cosmological magnetic fields: A Bayesian approach

Vacca

Oppermann

Enßlin

et al. 2016

A&A

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Determining magnetic field properties in different environments of the cosmic large-scale structure as well as their evolution over redshift is a fundamental step toward uncovering the origin of cosmic magnetic fields. Radio observations permit the study of extragalactic magnetic fields via measurements of the Faraday depth of extragalactic radio sources. Our aim is to investigate how much different extragalactic environments contribute to the Faraday depth variance of these sources. We develop a Bayesian algorithm to distinguish statistically Faraday depth variance contributions intrinsic to the source from those due to the medium between the source and the observer. In our algorithm the Galactic foreground and measurement noise are taken into account as the uncertainty correlations of the Galactic model. Additionally, our algorithm allows for the investigation of possible redshift evolution of the extragalactic contribution. This work presents the derivation of the algorithm and tests performed on mock observations. Because cosmic magnetism is one of the key science projects of the new generation of radio interferometers, we have predicted the performance of our algorithm on mock data collected with these instruments. According to our tests, high-quality catalogs of a few thousands of sources should already enable us to investigate magnetic fields in the cosmic structure.

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“…There is a strong interest in measuring and estimating the intergalactic magnetic field in clusters of galaxies or in cosmic filaments through RM analysis and tomography, e.g., Akahori et al (2014). In the presence of a single Faraday screen along the line of sight, the rotation angle of the radio polarization vector of extragalactic sources depends linearly on l 2 .…”

Section: Prospects For Rm Grid Experimentsmentioning

confidence: 99%

“…The term in parentheses is called the Faraday depth, f. For a single line of sight through a thin ionized screen, this is equivalent to the rotation measure, RM, defined by º c l the Galactic component, intervening extragalactic ionized gas, and material that is local to the source. Multiple studies such as Goodlet & Kaiser (2005), Kronberg et al (2008), Schnitzeler (2010), Bernet et al (2012), Hammond et al (2012), Bernardi et al (2013), Farnes et al (2014b), Banfield et al (2014), Akahori et al (2014), and Vacca et al (2015Vacca et al ( , 2016 have tried to identify and distinguish these separate components and study the evolution of the magnetic field of galaxies through cosmic time. When many lines of sight each have independent single Faraday depths, this problem is approached statistically.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Disorder and Faraday Effects on the Polarization of Extragalactic Radio Sources

Lamee

Rudnick

Farnes

et al. 2016

ApJ

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We present a polarization catalog of 533 extragalactic radio sources that have a 2.3 GHz total intensity above 420 mJy from the S-band Polarization All Sky Survey, S-PASS, with corresponding 1.4 GHz polarization information from the NRAO VLA Sky Survey, NVSS. We studied the selection effects and found that fractional polarization, π, of radio objects at both wavelengths depends on the spectral index, the source magnetic field disorder, the source size, and depolarization. The relationship between depolarization, spectrum, and size shows that depolarization occurs primarily in the source vicinity. The median p 2.3 of resolved objects in NVSS is approximately two times larger than that of unresolved sources. Sources with little depolarization are ∼2 times more polarized than both highly depolarized and re-polarized sources. This indicates that intrinsic magnetic field disorder is the dominant mechanism responsible for the observed low fractional polarization of radio sources at high frequencies. We predict that number counts from polarization surveys will be similar at 1.4 GHz and at 2.3 GHz, for fixed sensitivity, although ∼10% of all sources may currently be missing because of strong depolarization. Objects withtypically have simple Faraday structures, so they are most useful for background samples. Almost half of flat-spectrum (  a -0.5) and ∼25% of steep-spectrum objects are repolarized. Steep-spectrum, depolarized sources show a weak negative correlation of depolarization with redshift in the range 0 < z < 2.3. Previous non-detections of redshift evolution are likely due the inclusion of re-polarized sources as well.

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Exploring the intergalactic magnetic field by means of Faraday tomography

Cited by 39 publications

References 68 publications

Detecting the Magnetic Cosmic Web through Deep Radio Polarization Imaging

Detecting the Magnetic Cosmic Web through Deep Radio Polarization Imaging

Using rotation measure grids to detect cosmological magnetic fields: A Bayesian approach

Magnetic Field Disorder and Faraday Effects on the Polarization of Extragalactic Radio Sources

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