scholarly journals Constraints on large-scale magnetic fields in the intergalactic medium using cross-correlation methods

2021 ◽  
Vol 503 (2) ◽  
pp. 2913-2926
Author(s):  
A D Amaral ◽  
T Vernstrom ◽  
B M Gaensler
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Cross Correlation ◽  
Intergalactic Medium ◽  
Upper Bounds ◽  
Parallel Component ◽  
Weak Magnetic Fields ◽  
Upper Limits ◽  
Formation And Evolution ◽  
The Mean

ABSTRACT Large-scale coherent magnetic fields in the intergalactic medium (IGM) are presumed to play a key role in the formation and evolution of the cosmic web, and in large-scale feedback mechanisms. However, they are theorized to be extremely weak, in the nano-Gauss regime. To search for a statistical signature of these weak magnetic fields, we perform a cross-correlation between the Faraday rotation measures (RMs) of 1742 radio galaxies at z > 0.5 and large-scale structure at 0.1 < z < 0.5, as traced by 18 million optical and infrared foreground galaxies. No significant correlation signal was detected within the uncertainty limits. We are able to determine model-dependent 3σ upper limits on the parallel component of the mean magnetic field strength of filaments in the IGM of ∼30 nG for coherence scales between 1 and 2.5 Mpc, corresponding to a mean upper bound RM enhancement of ∼3.8 rad m−2 due to filaments along all probed sightlines. These upper bounds are consistent with upper bounds found previously using other techniques. Our method can be used to further constrain intergalactic magnetic fields with upcoming future radio polarization surveys.

scholarly journals Constraining the intergalactic medium at z ≈ 9.1 using LOFAR Epoch of Reionization observations

2020 ◽  
Vol 493 (4) ◽  
pp. 4728-4747 ◽  
Author(s):  
R Ghara ◽  
S K Giri ◽  
G Mellema ◽  
B Ciardi ◽  
S Zaroubi ◽  
...  
Keyword(s):  
Large Scale ◽  
Intergalactic Medium ◽  
Volume Fraction ◽  
Characteristic Size ◽  
Gas Temperature ◽  
Spin Temperature ◽  
Simulation Code ◽  
Upper Limits ◽  
Credible Intervals ◽  
Bayesian Inference Framework

ABSTRACT We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code grizzly and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≳0.13 and a distribution of the ionized regions with a characteristic size ≳ 8 h−1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≳16 h−1 Mpc is ruled out. For an IGM with a uniform spin temperature TS ≳ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≲0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h−1 Mpc and FWHM of ≲110 h−1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space.

scholarly journals Relativistic plasma and ICM/radio source interaction

2010 ◽  
Vol 6 (S274) ◽  
pp. 340-347 ◽  
Author(s):  
Luigina Feretti ◽  
Gabriele Giovannini ◽  
Federica Govoni ◽  
Matteo Murgia
Keyword(s):  
Magnetic Fields ◽  
Radio Source ◽  
Large Scale ◽  
Large Scale Structure ◽  
Radio Sources ◽  
Relativistic Electrons ◽  
Coma Cluster ◽  
Cluster Of Galaxies ◽  
Formation And Evolution ◽  
The Universe

AbstractThe first detection of a diffuse radio source in a cluster of galaxies, dates back to the 1959 (Coma Cluster, Large et al. 1959). Since then, synchrotron radiating radio sources have been found in several clusters, and represent an important cluster component which is linked to the thermal gas. Such sources indicate the existence of large scale magnetic fields and of a population of relativistic electrons in the cluster volume. The observational results provide evidence that these phenomena are related to turbulence and shock-structures in the intergalactic medium, thus playing a major role in the evolution of the large scale structure in the Universe. The interaction between radio sources and cluster gas is well established in particular at the center of cooling core clusters, where feedback from AGN is a necessary ingredient to adequately describe the formation and evolution of galaxies and host clusters.

scholarly journals Synthesizing Observations and Theory to Understand Galactic Magnetic Fields: Progress and Challenges

Galaxies ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 4 ◽  
Author(s):  
Rainer Beck ◽  
Luke Chamandy ◽  
Ed Elson ◽  
Eric G. Blackman
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Mean Field ◽  
Large Data ◽  
Data Sets ◽  
Dynamo Theory ◽  
Galactic Magnetic Fields ◽  
Ngc 6946 ◽  
Upper Limits ◽  
New Instruments

Constraining dynamo theories of magnetic field origin by observation is indispensable but challenging, in part because the basic quantities measured by observers and predicted by modelers are different. We clarify these differences and sketch out ways to bridge the divide. Based on archival and previously unpublished data, we then compile various important properties of galactic magnetic fields for nearby spiral galaxies. We consistently compute strengths of total, ordered, and regular fields, pitch angles of ordered and regular fields, and we summarize the present knowledge on azimuthal modes, field parities, and the properties of non-axisymmetric spiral features called magnetic arms. We review related aspects of dynamo theory, with a focus on mean-field models and their predictions for large-scale magnetic fields in galactic discs and halos. Furthermore, we measure the velocity dispersion of H i gas in arm and inter-arm regions in three galaxies, M 51, M 74, and NGC 6946, since spiral modulation of the root-mean-square turbulent speed has been proposed as a driver of non-axisymmetry in large-scale dynamos. We find no evidence for such a modulation and place upper limits on its strength, helping to narrow down the list of mechanisms to explain magnetic arms. Successes and remaining challenges of dynamo models with respect to explaining observations are briefly summarized, and possible strategies are suggested. With new instruments like the Square Kilometre Array (SKA), large data sets of magnetic and non-magnetic properties from thousands of galaxies will become available, to be compared with theory.

The Magnetic Sun from Different Views: A Comparison of the Mean and Background Magnetic Field Observations made in Different Observatories and in Different Spectral Lines

2000 ◽  
Vol 179 ◽  
pp. 209-212
Author(s):  
M. L. Demidov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Solar Observatory ◽  
Spectral Lines ◽  
The Sun ◽  
Background Magnetic Field ◽  
The Mean ◽  
Selection Of ◽  
Made In

AbstractA comparison is made of observational data on the mean magnetic field of the Sun from several observatories (a selection of published information and new measurements). Results of correlation and regression analyses of observations of background magnetic fields at the STOP telescope of the Sayan solar observatory in different spectral lines are also presented. Results obtained furnish an opportunity to obtain more unbiased information about large-scale magnetic fields of the Sun and, in particular, about manifestations of strong (kilogauss) magnetic fields in them.

scholarly journals Magnetic fields in astrophysical objects

2008 ◽  
Vol 366 (1884) ◽  
pp. 4453-4464 ◽  
Author(s):  
L.J Silvers
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Accretion Discs ◽  
Weak Magnetic Fields ◽  
Large Scale Magnetic Field ◽  
Astrophysical Objects ◽  
Recent Developments ◽  
The Magnetic Field

Magnetic fields are known to reside in many astrophysical objects and are now believed to be crucially important for the creation of phenomena on a wide variety of scales. However, the role of the magnetic field in the bodies that we observe has not always been clear. In certain situations, the importance of a magnetic field has been overlooked on the grounds that the large-scale magnetic field was believed to be too weak to play an important role in the dynamics. In this article I discuss some of the recent developments concerning magnetic fields in stars, planets and accretion discs. I choose to emphasize some of the situations where it has been suggested that weak magnetic fields may play a more significant role than previously thought. At the end of the article, I list some of the questions to be answered in the future.

scholarly journals An MHD Model of Be Stars with Disks

2000 ◽  
Vol 175 ◽  
pp. 611-616
Author(s):  
A. E. Dudorov ◽  
R. E. Pudritz
Keyword(s):  
Magnetic Fields ◽  
Accretion Disks ◽  
Large Scale ◽  
Be Stars ◽  
Magnetic Disk ◽  
X Ray ◽  
History Of ◽  
Formation And Evolution ◽  
Dynamical Features ◽  
A Current

AbstractAn investigation of the formation and evolution of Be stars show that these stars could have dipolar fossil magnetic fields. This magnetic field should constrain the circumstellar magnetic disk and influence its dynamical features. For studying these effects we refine the alphamodel of accretion disks of Shakura and Sunyaev by incorporating into this model the evolution of large-scale magnetic fields. In the frame of our model we can investigate the rotational history of the star with the disk and the ionization and thermal properties of disks. We show in particular that in the magnetopause region a current sheet can form that can generate X-ray radiation.

scholarly journals Reconstruction of baryon fraction in intergalactic medium through dispersion measurements of fast radio bursts

2021 ◽  
Vol 503 (3) ◽  
pp. 4576-4580
Author(s):  
Ji-Ping Dai ◽  
Jun-Qing Xia
Keyword(s):  
Standard Deviation ◽  
Relative Standard Deviation ◽  
Mass Fraction ◽  
Large Scale ◽  
Intergalactic Medium ◽  
Radio Bursts ◽  
Local Principle ◽  
Relative Standard ◽  
Baryon Mass ◽  
The Mean

ABSTRACT Fast radio bursts (FRBs) probe the total column density of free electrons in the intergalactic medium (IGM) along the path of propagation through the dispersion measures (DMs) that depend on the baryon mass fraction in the IGM, i.e. fIGM. In this letter, we investigate the large-scale clustering information of DMs to study the evolution of fIGM. When combining with the Planck 2018 measurements, we could give tight constraints on the evolution of fIGM(z) from about 104 FRBs with the intrinsic DM scatter of $30(1+z) \rm pc\, cm^{-3}$ spanning 80 per cent of the sky and redshift range z = 0–3. First, we consider the Taylor expansion of fIGM(z) up to second order, and find that the mean relative standard deviation σ(fIGM) ≡ 〈σ[fIGM(z)]/fIGM(z)〉 is about 6.7 per cent. In order to alleviate the dependence on fiducial model, we also adopt non-parametric methods in this work, the local principle component analysis. We obtain the consistent, but weaker constraints on the evolution of fIGM(z), namely the mean relative standard deviation σ(fIGM) is 21.4 per cent. With the forthcoming surveys, this could be a complimentary method to investigate the baryon mass fraction in the IGM.

scholarly journals The LOFAR view of intergalactic magnetic fields with giant radio galaxies

2020 ◽  
Vol 638 ◽  
pp. A48 ◽  
Author(s):  
C. Stuardi ◽  
S. P. O’Sullivan ◽  
A. Bonafede ◽  
M. Brüggen ◽  
P. Dabhade ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Detection Rate ◽  
Intergalactic Medium ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Weak Magnetic Fields ◽  
Polarization Study ◽  
Sky Survey

Context. Giant radio galaxies (GRGs) are physically large radio sources that extend well beyond their host galaxy environment. Their polarization properties are affected by the poorly constrained magnetic field that permeates the intergalactic medium on megaparsec scales. A low frequency (< 200 MHz) polarization study of this class of radio sources is now possible with LOFAR. Aims. Here we investigate the polarization properties and Faraday rotation measure (RM) of a catalog of GRGs detected in the LOFAR Two-meter Sky Survey. This is the first low frequency polarization study of a large sample of radio galaxies that were selected on their physical size. We explore the magneto-ionic properties of their under-dense environment and probe intergalactic magnetic fields using the Faraday rotation properties of their radio lobes. LOFAR is a key instrument for this kind of analysis because it can probe small amounts of Faraday dispersion (< 1 rad m−2), which are associated with weak magnetic fields and low thermal gas densities. Methods. We used RM synthesis in the 120−168 MHz band to search for polarized emission and to derive the RM and fractional polarization of each detected source component. We study the depolarization between 1.4 GHz and 144 MHz using images from the NRAO VLA Sky Survey. We investigate the correlation of the detection rate, the RM difference between the lobes, and the depolarization with different parameters as follows: the angular and linear size of the sources and the projected distance from the closest foreground galaxy cluster. In our sample, we also included 3C 236, which is one of the largest radio galaxies known. Results. From a sample of 240 GRGs, we detected 37 sources in polarization, all of which have a total flux density above 56 mJy. We detected significant RM differences between the lobes, which would be inaccessible at gigahertz frequencies, with a median value of ∼1 rad m−2. The fractional polarization of the detected GRGs at 1.4 GHz and 144 MHz is consistent with a small amount of Faraday depolarization (a Faraday dispersion < 0.3 rad m−2). Our analysis shows that the lobes are expanding into a low-density (< 10−5 cm−3) local environment that is permeated by weak magnetic fields (< 0.1 μG) with fluctuations on scales of 3−25 kpc. The presence of foreground galaxy clusters appears to influence the polarization detection rate up to 2R500. In general, this work demonstrates the ability of LOFAR to quantify the rarefied environments in which these GRGs exist and highlights them as an excellent statistical sample to use as high precision probes of magnetic fields in the intergalactic medium and the Milky Way.

Magnetic fields in the intergalactic medium and in the cosmic web

2018 ◽  
Vol 14 (A30) ◽  
pp. 303-306
Author(s):  
Marcus Brüggen ◽  
Shane O’Sullivan ◽  
Annalisa Bonafede ◽  
Franco Vazza
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Intergalactic Medium ◽  
Angular Resolution ◽  
Low Frequency ◽  
Small Scale ◽  
Rotation Measurement ◽  
Field Amplification ◽  
Unique Capability

AbstractIn these proceedings we discuss advances in the theory and observation of magnetic fields in the intergalactic medium and in the cosmic web. We make the point that, despite perhaps unsurmountable obstacles in simulating a small-scale dynamo, currently most cosmological magnetohydrodynamical simulations paint a similar picture of magnetic field amplification in the cosmos. However, observations of magnetic fields in the intergalactic medium turn out to be very difficult. As a case in point, we present recent work on Faraday rotation measurement in the direction of a giant galaxy with the Low Frequency Array (LOFAR). These observations demonstrate the currently unique capability of LOFAR to measure Faraday rotation at the high accuracy and angular resolution required to investigate the magnetisation of large-scale structure filaments of the cosmic web.

scholarly journals The dichotomy between strong and ultra-weak magnetic fields among intermediate-mass stars

2013 ◽  
Vol 9 (S302) ◽  
pp. 338-347 ◽  
Author(s):  
François Lignières ◽  
Pascal Petit ◽  
Michel Aurière ◽  
Gregg A. Wade ◽  
Torsten Böhm
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Large Scale ◽  
Field Measurements ◽  
Mass Range ◽  
Mass Star ◽  
Rotating Stars ◽  
Intermediate Mass ◽  
Weak Magnetic Fields ◽  
Chemically Peculiar Stars

AbstractUntil recently, the detection of magnetic fields at the surface of intermediate-mass main-sequence stars has been limited to Ap/Bp stars, a class of chemically peculiar stars. This class represents no more than 5-10% of the stars in this mass range. This small fraction is not explained by the fossil field paradigm that describes the Ap/Bp type magnetism as a remnant of an early phase of the star-life. Also, the limitation of the field measurements to a small and special group of stars is obviously a problem to study the effect of the magnetic fields on the stellar evolution of a typical intermediate-mass star.Thanks to the improved sensitivity of a new generation of spectropolarimeters, a lower bound to the magnetic fields of Ap/Bp stars, a two orders of magnitude desert in the longitudinal magnetic field and a new type of sub-gauss magnetism first discovered on Vega have been identified. These advances provide new clues to understand the origin of intermediate-mass magnetism as well as its influence on stellar evolution. In particular, a scenario has been proposed whereby the magnetic dichotomy between Ap/Bp and Vega-like magnetism originate from the bifurcation between stable and unstable large scale magnetic configurations in differentially rotating stars. In this paper, we review these recent observational findings and discuss this scenario.

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