scholarly journals The intergalactic magnetic field probed by a giant radio galaxy

2019 ◽  
Vol 622 ◽  
pp. A16 ◽  
Author(s):  
S. P. O’Sullivan ◽  
J. Machalski ◽  
C. L. Van Eck ◽  
G. Heald ◽  
M. Brüggen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Radio Galaxy ◽  
Small Scale ◽  
Cosmological Simulations ◽  
Rotation Measure ◽  
Sky Survey ◽  
Intergalactic Magnetic Field ◽  
Using Data ◽  
The Universe

Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). Using data from the LOFAR Two Metre Sky Survey (LoTSS), we present the Faraday rotation measure (RM) and depolarisation properties of the giant radio galaxy J1235+5317, at a redshift of z = 0.34 and 3.38 Mpc in size. We find a mean RM difference between the lobes of 2.5 ± 0.1 rad m−2, in addition to small scale RM variations of ∼0.1 rad m−2 . From a catalogue of LSS filaments based on optical spectroscopic observations in the local universe, we find an excess of filaments intersecting the line of sight to only one of the lobes. Associating the entire RM difference to these LSS filaments leads to a gas density-weighted IGMF strength of ∼0.3 μG. However, direct comparison with cosmological simulations of the RM contribution from LSS filaments gives a low probability (∼5%) for an RM contribution as large as 2.5 rad m−2, for the case of IGMF strengths of 10–50 nG. It is likely that variations in the RM from the Milky Way (on 11′ scales) contribute significantly to the mean RM difference, and a denser RM grid is required to better constrain this contribution. In general, this work demonstrates the potential of the LOFAR telescope to probe the weak signature of the IGMF. Future studies, with thousands of sources with high accuracy RMs from LoTSS, will enable more stringent constraints on the nature of the IGMF.

scholarly journals Strategy to Explore Magnetized Cosmic Web with Forthcoming Large Surveys of Rotation Measure

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 118 ◽  
Author(s):  
Takuya Akahori
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Line Of Sight ◽  
Wide Field ◽  
Sky Surveys ◽  
Rotation Measure ◽  
Polarized Emission ◽  
Linearly Polarized ◽  
Intergalactic Magnetic Field ◽  
The Universe

The warm-hot intergalactic medium (WHIM) is a candidate for the missing baryons in the Universe. If the WHIM is permeated with the intergalactic magnetic field (IGMF), the Faraday rotation measure (RM) of the WHIM is imprinted in linearly-polarized emission from extragalactic objects. In this article, we discuss strategies to explore the WHIM’s RM from forthcoming radio broadband and wide-field polarization sky surveys. There will be two observational breakthroughs in the coming decades; the RM grid and Faraday tomography. They will allow us to find ideal RM sources for the study of the IGMF and give us unique information of the WHIM along the line of sight.

scholarly journals X-Ray and Radio Emissions of AWM and MKW Clusters

2012 ◽  
Author(s):  
Michael Ramuta
Keyword(s):  
Large Scale ◽  
Life Cycles ◽  
Sloan Digital Sky Survey ◽  
X Ray ◽  
Large Scale Structures ◽  
Sky Survey ◽  
Scale Structures ◽  
Using Data ◽  
And Behavior ◽  
The Universe

A grasp of the life-cycles of large-scale structures is critical to understanding the Universe. This can be accomplished through the study of poor clusters-- that is, younger clusters that are likely evolving to another state. The selected clusters are significant in that they are poor but also possess a type-cD galaxy. This brighter central galaxy suggests that these clusters may be dynamically evolved and are potential candidates for fossil groups. In order to more fully understand the structure and behavior of poor galaxy clusters, 12 clusters were selected and analyzed. Using data from the Sloan Digital Sky Survey, Chandra X-Ray Archive, and the VLA FIRST Survey, we present x-ray profiles and radio observations of these 12 galaxy clusters. 

scholarly journals New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations

2020 ◽  
Vol 495 (3) ◽  
pp. 2607-2619 ◽  
Author(s):  
S P O’Sullivan ◽  
M Brüggen ◽  
F Vazza ◽  
E Carretti ◽  
N T Locatelli ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Current Data ◽  
Inhomogeneous Universe ◽  
Origin And Evolution ◽  
Rotation Measure ◽  
Sky Survey ◽  
Significant Difference

ABSTRACT Measuring the properties of extragalactic magnetic fields through the effect of Faraday rotation provides a means to understand the origin and evolution of cosmic magnetism. Here, we use data from the LOFAR Two-Metre Sky Survey (LoTSS) to calculate the Faraday rotation measure (RM) of close pairs of extragalactic radio sources. By considering the RM difference (ΔRM) between physical pairs (e.g. double-lobed radio galaxies) and non-physical pairs (i.e. close projected sources on the sky), we statistically isolate the contribution of extragalactic magnetic fields to ΔRM along the line of sight between non-physical pairs. From our analysis, we find no significant difference between the ΔRM distributions of the physical and non-physical pairs, limiting the excess Faraday rotation contribution to <1.9 rad m−2 (${\sim}95{{\ \rm per\ cent}}$ confidence). We use this limit with a simple model of an inhomogeneous universe to place an upper limit of 4 nG on the cosmological co-moving magnetic field strength on Mpc scales. We also compare the RM data with a more realistic suite of cosmological magnetohydrodynamical simulations that explore different magnetogenesis scenarios. Both magnetization of the large-scale structure by astrophysical processes such as galactic and AGN outflows, and simple primordial scenarios with seed magnetic field strengths <0.5 nG cannot be rejected by the current data; while stronger primordial fields or models with dynamo amplification in filaments are disfavoured.

Fluctuations in the Galactic Magnetic Field

1990 ◽  
Vol 140 ◽  
pp. 55-58
Author(s):  
James M. Cordes ◽  
Andrew Clegg ◽  
John Simonetti
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Measure Data ◽  
Small Scale ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
Scale Field ◽  
Large Scale Field ◽  
The Magnetic Field

We discuss small scale structure in the Galactic magnetic field as inferred from Faraday rotation measurements of extragalactic radio sources. The rotation measure data suggest a continuum of length scales extending from parsec scales down to at least 0.01 pc and perhaps to as small as 109 cm. Such turbulence in the magnetic field comprises a reservoir of energy that is comparable to the energy in the large scale field.

Student Perceptions of Community: A Different Perspective

NASPA Journal ◽  
1998 ◽  
Vol 35 (4) ◽  
Author(s):  
Jackie Clark ◽  
Joan Hirt
Keyword(s):  
Student Perceptions ◽  
Large Scale ◽  
Research University ◽  
Small Scale ◽  
Social Environments ◽  
Common Assumption ◽  
Small Communities ◽  
Public Research University ◽  
The Common ◽  
Using Data

The creation of small communities has been proposed as a way of enhancing the educational experience of students at large institutions. Using data from a survey of students living in large and small residences at a public research university, this study does not support the common assumption that small-scale social environments are more conducive to positive community life than large-scale social environments.

scholarly journals On the origin of variable structures in the winds of hot luminous stars

2013 ◽  
Vol 440 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Yannick J. L. Michaux ◽  
Anthony F. J. Moffat ◽  
André-Nicolas Chené ◽  
Nicole St-Louis
Keyword(s):  
Magnetic Field ◽  
Empirical Evidence ◽  
Temporal Variability ◽  
Large Scale ◽  
Small Scale ◽  
Ionization Zone ◽  
Corotating Interaction Regions ◽  
Wind Variability ◽  
Global Magnetic Field ◽  
Interaction Regions

Abstract Examination of the temporal variability properties of several strong optical recombination lines in a large sample of Galactic Wolf–Rayet (WR) stars reveals possible trends, especially in the more homogeneous WC than the diverse WN subtypes, of increasing wind variability with cooler subtypes. This could imply that a serious contender for the driver of the variations is stochastic, magnetic subsurface convection associated with the 170 kK partial-ionization zone of iron, which should occupy a deeper and larger zone of greater mass in cooler WR subtypes. This empirical evidence suggests that the heretofore proposed ubiquitous driver of wind variability, radiative instabilities, may not be the only mechanism playing a role in the stochastic multiple small-scaled structures seen in the winds of hot luminous stars. In addition to small-scale stochastic behaviour, subsurface convection guided by a global magnetic field with localized emerging loops may also be at the origin of the large-scale corotating interaction regions as seen frequently in O stars and occasionally in the winds of their descendant WR stars.

scholarly journals How to make the Sun look less like the Sun and more like a star?

2016 ◽  
Vol 12 (S328) ◽  
pp. 237-239
Author(s):  
A. A. Vidotto
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Vector Fields ◽  
Radial Component ◽  
Field Vector ◽  
Small Scale ◽  
General Context ◽  
The Sun ◽  
Flux Transport ◽  
Large Scale Magnetic Field

AbstractSynoptic maps of the vector magnetic field have routinely been made available from stellar observations and recently have started to be obtained for the solar photospheric field. Although solar magnetic maps show a multitude of details, stellar maps are limited to imaging large-scale fields only. In spite of their lower resolution, magnetic field imaging of solar-type stars allow us to put the Sun in a much more general context. However, direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, I present the results of a method to filter out the small-scale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. This approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well, and is entirely consistent with the description adopted in several stellar studies. This method can also be used to confront synoptic maps synthesised in numerical simulations of dynamo and magnetic flux transport studies to those derived from stellar observations.

scholarly journals Multifractal analysis of radar rainfall fields over the area of Rome

2005 ◽  
Vol 2 ◽  
pp. 293-299 ◽  
Author(s):  
G. Calenda ◽  
E. Gorgucci ◽  
F. Napolitano ◽  
A. Novella ◽  
E. Volpi
Keyword(s):  
Scale Invariance ◽  
Large Scale ◽  
Doppler Radar ◽  
Risk Mitigation ◽  
Small Scale ◽  
Radar Rainfall ◽  
Invariance Properties ◽  
Meteorological Radar ◽  
Using Data ◽  
Precipitation Events

Abstract. A scale-invariance analysis of space and time rainfall events monitored by meteorological radar over the area of Rome (Italy) is proposed. The study of the scale-invariance properties of intense precipitation storms, particularly important in flood forecast and risk mitigation, allows to transfer rainfall information from the large scale predictive meteorological models to the small scale hydrological rainfall-runoff models. Precipitation events are monitored using data collected by the polarimetric Doppler radar Polar 55C (ISAC-CNR), located 15 km Southeast from downtown. The meteorological radar provides the estimates of rainfall intensity over an area of about 10 000 km2 at a resolution of 2×2 km2 in space and 5 min in time. Many precipitation events have been observed from autumn 2001 up to now. A scale-invariance analysis is performed on some of these events with the aim at exploring the multifractal properties and at understanding their dependence on the meteorological large-scale conditions.

STATIONARY SHEATH OF FARADAY ROTATION IN THE JET OF 3C 120

2010 ◽  
Vol 19 (06) ◽  
pp. 917-922
Author(s):  
JOSÉ L. GÓMEZ ◽  
MAR ROCA-SOGORB ◽  
IVÁN AGUDO ◽  
ALAN P. MARSCHER ◽  
SVETLANA G. JORSTAD
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Radio Galaxy ◽  
External Medium ◽  
Degree Of Polarization ◽  
Polarization Structure ◽  
Rotation Measure ◽  
Helical Magnetic Field ◽  
3C 120 ◽  
Two Fluid

We present a sequence of 12 monthly polarimetric multi-frequency VLBA observations of the radio galaxy 3C 120. The motion of multiple superluminal components allows the mapping of the polarization structure along most of the jet and across its width, revealing a coherent in time Faraday screen and RM-corrected polarization angles. Gradients in Faraday rotation and degree of polarization across the jet are observed, together with a localized region of high rotation measure superposed on this structure. This is explained as produced by the presence of a helical magnetic field in a two-fluid jet model, consisting of an inner emitting jet and a sheath containing nonrelativistic electrons. Interaction of the jet with the external medium would explain the confined region of enhanced Faraday rotation.

scholarly journals Mean-Field Magnetohydrodynamics as a Basis of Solar Dynamo Theory

1976 ◽  
Vol 71 ◽  
pp. 323-344 ◽  
Author(s):  
K.-H. Rädler
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Mean Field ◽  
Strong Relationship ◽  
Solar Radius ◽  
Small Scale ◽  
Dynamo Theory ◽  
The Magnetic Field ◽  
Complicated Situation ◽  
Insight Into

One of the most striking features of both the magnetic field and the motions observed at the Sun is their highly irregular or random character which indicates the presence of rather complicated magnetohydrodynamic processes. Of great importance in this context is a comprehension of the behaviour of the large scale components of the magnetic field; large scales are understood here as length scales in the order of the solar radius and time scales of a few years. Since there is a strong relationship between these components and the solar 22-years cycle, an insight into the mechanism controlling these components also provides for an insight into the mechanism of the cycle. The large scale components of the magnetic field are determined not only by their interaction with the large scale components of motion. On the contrary, a very important part is played also by an interaction between the large and the small scale components of magnetic field and motion so that a very complicated situation has to be considered.

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