Faraday Rotation Measure Synthesis of Intermediate Redshift Quasars as a Probe of Intervening Matter

Kim, Kwang Seong; Lilly, S. J.; Miniati, Francesco; Bernet, M.; Beck, Rainer; O’Sullivan, Shane; Gaensler, B. M.

doi:10.3847/0004-637x/829/2/133

Cited by 43 publications

(53 citation statements)

References 41 publications

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“…Robishaw et al (2008) detected field strengths up to 18 mG in starburst galaxies but ordered galactic magnetic fields in the ISM are typically expected to be of the order of several µG, similar in strength to the fluctuating components. Kim et al (2016) found in intermediate redshift galaxies a clear correlation between large magnetic field strength and Mg II absorption, which indicates a link between strong outflows and a high magnetisation, as well as field as strong as a few 10 −6 G at epochs as early as z 4 − 5.…”

Section: Introductionmentioning

confidence: 83%

A small-scale dynamo in feedback-dominated galaxies – III. Cosmological simulations

Rieder

Teyssier

2017

Monthly Notices of the Royal Astronomical Society

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Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific genesis has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations.We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement (AMR) technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a small-scale dynamo process and is finally carried out into the circumgalactic medium by a galactic wind.This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the small scale dynamo process, that high-redshift magnetic fields are likely to be dominated by their small scale components.

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Section: Introductionmentioning

confidence: 83%

A small-scale dynamo in feedback-dominated galaxies – III. Cosmological simulations

Rieder

Teyssier

2017

Monthly Notices of the Royal Astronomical Society

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“…Apart from the RRM measurement for these quasars sightlines, their observed fractional polarisation (p) is another parameter which might also be a useful tool to probe the magnetic field in the intervening galaxies, again by comparing p values and its correlation with RRM for subsample with and without Mg ii absorbers. Many past studies have explored this possibility and found that indeed higher RRM is associated with the lesser p value (Hammond et al 2012;Bernet et al 2013;Kim et al 2016). For instance, Hammond et al (2012) found an anti-correlation between RRM and fractional polarization.…”

Section: Introductionmentioning

confidence: 97%

Role of Intervening Mg ii Absorbers on the Rotation Measure and Fractional Polarization of the Background Quasars

Malik

Chand

Seshadri

2020

ApJ

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Excess extragalactic contribution to residual rotation measure (RRM) for quasars sightlines with intervening Mg ii absorbers is a powerful tool to investigate the presence of magneto-active plasma in high-redshift galaxies. To carry out such an analysis, we have compiled a large sample of 1132 quasars for which we have RRM data as well as optical spectra capable of ascertaining the presence/absence of any intervening Mg ii absorbers. In this study, we found that the dispersion in RRM (σ rrm ) for 314 sightlines having Mg ii intervening absorbers is 15.78±0.92 rad m −2 as compared to its value of 14.62 ± 0.70 rad m −2 for the 818 sightlines without such absorbers, resulting in an excess standard deviation (σ ex rrm ) of 5.93 ± 2.99 rad m −2 among these two subsamples. A similar analysis on subsample split based on the radio spectral index (F ∝ ν α ) for flat (α ≥ −0.3; 312 sources) and steep (α ≤ −0.7; 469 sources) show non-significant dependence of spectral index on σ exrrm . An anti-correlation is found between the dispersion in RRM and fractional polarisation (p) with Pearson correlation coefficient (ρ p ) of −0.70 and −0.87 for the subsample with and without Mg ii absorbers, respectively. This nominal impact of Mg ii absorbers on ρ p suggests that the main contribution for the decrement in the p value is intrinsic to the local environment of the quasars. Based on our subsample of quasars without Mg ii absorbers, we found that neither σ rrm nor the median value of the p, indicates any evolution with quasars emission redshift. However, a very significant correlation with ρ p = 0.85 is found among σ rrm and the Mg ii absorber redshift. This can be useful to place strong constraint on models of magnetic field evolution in the high-redshift galaxies.

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“…All RM synthesis calculations were performed using the pyrmsynth package. 4 We made use of Astropy, NumPy, matplotlib and joblib in preparing this manuscript.…”

Section: Acknowledgmentsmentioning

confidence: 99%

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

et al. 2019

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In this paper we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. In order to directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although the majority of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially-local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to presence of a Faraday rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously. of 30medium for a large number of sources in a much reduced amount of observing time. Broad-band spectro-polarimetry has played a crucial role in unveiling the properties of magnetic fields in nearby galaxies [1][2][3], in high redshift galaxies [4,5], in active galactic nuclei [AGN; 6-8] and the intergalactic medium [9]. In order to physically interpret such data, the technique of Faraday rotation measure (RM) synthesis [10,11] and direct fitting of the Stokes Q and U spectra of a polarized source with models of the magneto-ionic media, known as Stokes Q, U fitting [6,12,13] have been developed. It is often not straightforward to interpret the results from these techniques and connect them to the physical properties of the magnetized plasmas being investigated [14].Currently, several large-scale spectro-polarimetric campaigns are underway, mostly in the 1 to 5 GHz frequency range. On one hand, dedicated surveys with interferometers are being conducted to study the broad-band polarization properties of millions of extragalactic sources. For example, the Karl G. Jansky Very Large Array Sky Survey [VLASS; 15,16], the Polarization Sky Survey of the Universe's Magnetism [POSSUM; 17], the QU Observations at Cm wavelength with Km baselines using ATCA 1 (QUOCKA), the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey [18], and the recent LOFAR Two-meter Sky Survey [L...

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Faraday Rotation Measure Synthesis of Intermediate Redshift Quasars as a Probe of Intervening Matter

Cited by 43 publications

References 41 publications

A small-scale dynamo in feedback-dominated galaxies – III. Cosmological simulations

A small-scale dynamo in feedback-dominated galaxies – III. Cosmological simulations

Role of Intervening Mg ii Absorbers on the Rotation Measure and Fractional Polarization of the Background Quasars

An In-Depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations

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