COSMOLOGICAL MAGNETIC FIELDS

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International conference on
COSMOLOGICAL MAGNETIC FIELDS
Centro Stefano Franscini
Monte Verita,Ascona,Switzerland
May 31 { June 5 2009
Organized by
Axel Brandenburg,Ruth Durrer and Roy Maartens
Francine Gennai (secretary),Andreas Malaspinas (webmaster)
Also sponsored by the
and the Marc Birkigt foundation.
Preface
 Observation of large scale magnetic elds
Observation of magnetic elds is a notoriously dicult problem.Magnetic elds can be measured by
use of the induced Faraday rotation,but then they need to be traversed by polarized radio emission,
the Faraday rotation of which can then be measured.Faraday rotation in principle just measures the
magnetic eld integrated along the line of sight.Another procedure is to measure synchrotron emission.
Synchrotron emission is insensitive to the magnetic eld direction.In spite of these diculties,magnetic
elds of Gauss strength have been observed in many galaxies and even in proto galaxies at considerable
redshift.Also in galaxy clusters magnetic elds with strength of 0.1 to 1 Gauss have been observed.It is
interesting to note that the magnetic eld strengths inferred from Faraday rotation and from synchrotron
emission are not always compatible.
There are several talks updating us with the present stage of these observations.We also will have a talk
about future prospects which are especially bright with the expansion of the Very Large Array (EVLA),
the upcoming Low Frequency array (LOFAR) and the future Square Kilometer Array (SKA).
 Primordial magnetic elds
It is possible that magnetic elds have been generated very early in the universe and that they have been
amplied during structure formation to give raise to the observed Gauss elds in galaxies.If these elds
are generated during galaxy formation simply by ux conservation,primordial elds with amplitudes of
about 10
9
Gauss are needed.However,if they are amplied by the action of a dynamo,much smaller
elds may suce.
There have been proposals that sucient magnetic elds can be generated either during in ation or
during the electroweak phase transition.We have talks on these and other suggestions.On the other
hand,primordial magnetic elds have been constrained severely by the gravity waves which they induce
during the expansion of the universe.
 Cosmic magnetism and the CMB
Magnetic elds aect in several very distinct ways the cosmic microwave background (CMB).They modify
polarization via Faraday rotation,they induce vector perturbations in the cosmic plasma with Alfen waves
and they lead to a shift of the sound speed of radiation (fast magneto-sonic waves).In addition their
energy momentum tensor modies the gravitational eld which aects the Sachs Wolfe contribution the
the CMB anisotropies.Since CMB anisotropy and polarization data is so accurate (and is soon to become
even more so),we have talks on all these eects and discussions investigating how CMB observations can
help us to constrain or even measure primordial magnetic elds or magnetic elds in clusters of galaxies.
 Evolution of cosmological magnetic elds
There are several talks on studies of the evolution of cosmological magnetic elds with numerical and
analytical methods.Of special interest is the fact that helical magnetic elds can invoke an inverse
cascade and thereby transport power from small to large scales.If this mechanism is suciently ecient
it may provide a way out of the stringent constraints on primordial magnetic elds which come mainly
from the fact that these usually have most of their energy on very small scales while we observe magnetic
elds with large coherence scales in galaxies and clusters.
 Cosmic magnetism and non-linear structure formation
It might be,that charge separation processes during structure formation introduce a current which in turn
leads to the formation of magnetic elds.It is well known,that this eect vanishes in linear perturbation
theory.However,beyond linear perturbation theory there are several mechanisms (e.g.the Harrison
mechanism,Biermann mechanism) which can generate magnetic elds.
We acknowledge nancial support from ETH Zurich,Geneva University and the Marc Birkigt Foundation.
Monday,June 1
9:15{9:30
Welcome
9:30{10:50
Philipp Kronberg
Large scale magnetic elds:
from galaxies to superclusters
10:50{11:10
Coee break
11:10{12:00
Luigina Feretti
Magnetic elds in clusters of galaxies
12:30
Lunch
15:00{18:00
parallel
Observations (Gabriele Giovannini)
sessions
Primordial magnetic elds (Axel Brandeburg)
19:30
Dinner
Tuesday,June 2
9:10{10:00
Andrew Fletcher
Observing Cosmological Magnetic Fields
with Future Radio Facilities
10:00{10:50
Torsten Ensslin
Turbulent magnetic elds in galaxy clusters
10:50{11:10
Coee break
11:10{12:00
Romain Teyssier
Cosmological MHD simulations
12:30
Lunch
15:00{ 18:00
parallel
Numerical methods (Klaus Dolag)
sessions
Cosmic magnetic elds and the CMB (Roy Maartens)
19:00
Dinner
20:30
Gabriele Giovannini
Calamite giganti nell'Universo
public talk
Wednesday,June 3
9:10{10:00
Kerstin Kunze
Magnetic elds and the CMB
10:00{10:50
Fabio Finelli
Scalar perturbations in the CMB from
magnetic elds
10:50{11:10
Coee break
11:10{12:00
Tina Kahniashvili
Cosmological signatures of primordial helical magnetic elds
12:30
Lunch
14:00{?
Excursion
 19:30
Dinner
Thursday,June 4
9:10{10:00
Tanmay Vachaspati
Primordial magnetic elds and baryogenesis
10:00{10:50
Juan Garcia-Bellido
Magnetic eld production during preheating
at the electroweak scale
10:50{11:10
Coee break
11:10{12:00
Chiara Caprini
Primordial magnetic elds and gravitational waves
12:30
Lunch
15:00{18:00
parallel session
Magnetic elds and structure formation (Christos Tsagas)
19:30
Conference Dinner
Friday,June 5
9:10{10:00
Keitaro Takahashi
Magnetic elds from cosmological perturbations
10:00{10:50
Karsten Jedamzik
Evolution of magnetic eld spectra
10:50{11:10
Coee break
11:10{12:00
Kandu Subramanian
Primordial magnetic elds:Origin and structure formation signals
12:30
Lunch
The END
3
1 Plenary sessions
1.1 Monday June 1
Large scale magnetic elds:from galaxies to superclusters
Philipp Kronberg,University of Toronto and Los Alamos National Laboratory
It is likely that intergalactic magnetic elds are naturally seeded by (1)\normal"stellar processes in galaxies,
and (2) by central galactic black holes.There may also be (3) a primordial component from the pre-galactic
Universe,but this is probably overwhelmed by the rst two processes,except possibly in cosmic voids.
I discuss methods for probing diuse astrophysical magnetic elds,and some relevant theoretical ideas and
calculations.The starting point will be new results on the magnetic structure of our Galaxy,then external
galaxies,the IGM,and magnetic elds in galaxy systems at redshifts up to 3.I describe how information on
extragalactic magnetic structures suggests possible UHECR acceleration sites.
Magnetic elds in cluster of galaxies
Luigina Feretti,Istituto di Radioastronomia - INAF
The origin and evolution of magnetic elds in the Universe is one of the most fascinating and currently unsolved
problems in astrophysics.The existence of kpc-scale elds,in particular,raises several problems because of
the need of amplication mechanisms acting with large eciency on large scales.Clusters of galaxies,being
the largest systems in the Universe,represent an ideal laboratory to test theories for the origin of extragalactic
magnetic elds.Magnetic elds are investigated in the radio band from studies of the diuse synchrotron
emission and from the rotation measure of polarized radio sources.I will review the current results obtained
from radio observations,showing that cluster elds are at the G level,with values up to tens of G at the
center of cooling core clusters.
1.2 Tuesday June 2
Observing Cosmological Magnetic Fields with Future Radio Facilities
Andrew Fletcher,Newcastle University
Magnetic elds can be traced via diuse and point-source synchrotron radiation at radio wavelengths via its
intensity,polarization,depolarization and Faraday rotation.Consequently,studies of cosmic magnetism are
one of the prominent science drivers for a new generation of radio observatories,from the low-frequency array
LOFAR,currently under construction,to the Square Kilometer Array and its planned pathnder telescopes.
I will discuss the possibilities for testing theoretical ideas with these new instruments and some of the new
methods that will be available to broaden our observational knowledge of cosmic magnetic elds and their
origin.
Turbulent magnetic elds in galaxy clusters
Torsten Ensslin,Max-Planck-Institut fur Astrophysik,Garching
Galaxy clusters are large laboratories for magnetic plasma turbulence and therefore permit us to confront
our theoretical concepts of magnetogenesis with detailed observations.Magnetic turbulence in clusters can be
studied via the radio-synchrotron emission from the intra-cluster medium in the form of cluster radio relics
and halos.The power spectrum of turbulent magnetic elds can be examined via Faraday rotation analysis of
extended radio sources.In case of the Hydra A cool core,the observed magnetic spectrum can be understood
in terms of a turbulence-mediated feedback loop between gas cooling and the jet activity of the central galaxy.
Finally,methods to measure higher-order statistics of the magnetic eld using Stokes-parameter correlations are
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discussed,which permit us to determine the power spectrum of the magnetic tension force.This fourth-order
statistical quantity oers a way to discriminate between dierent magnetic turbulence scenarios and dierent
eld structures using radio polarimetric observations.
MHD simulation of structure formation:from large clusters to dwarf galaxies.
Romain Teyssier,University of Zurich
MHD simulation of structure formation:from large clusters to dwarf galaxies.The evolution of the magnetic
eld in the universe is believed to proceed through a rst phase of eld generation through microscopic processes
(Biermann Battery) at early time (cosmic reionization) followed by a second phase of a magnetic (alpha-omega)
dynamo in galactic disks.During the last 10 years,cosmological simulations of structure formation including the
evolution of the magnetic eld have been performed.The goal is to understand the evolution of the magnetic
eld within the hierarchical picture of galaxy formation.The rst attempts have focused on the generation
of magnetic elds at the epoch of reionization,on one hand,and on the amplication of magnetic elds by
merger-driven turbulence in galaxy clusters on the other hand.The evolution of magnetic elds in galaxies has
been only recently investigated by several groups.I will discuss some of the numerical aspects of cosmological
MHD,and present recent results obtained in MHD simulations of clusters and galaxies within a cosmological
context.
1.3 Wednesday June 3
Magnetic elds and the CMB
Kerstin Kunze,University of Salamanca
Primordial magnetic elds which are present since before matter-radiation equality aect the spectrum of tem-
perature anisotropies and the polarization of the cosmic microwave background (CMB).In particular,the eect
of a stochastic magnetic eld on the scalar perturbations of the geometry will be discussed and the resulting
angular power spectra of temperature uctuations and polarization presented.Furthermore,a primordial mag-
netic eld causes Faraday rotation of the orientation of the CMB polarization which leads to the creation of a
B-mode.Results will be presented and compared with data.
Scalar perturbations in the CMB from magnetic elds
Fabio Finelli,ASF Bologna & Astronomical Observatory Bologna
We review the impact of a stochastic background of primordial magnetic elds on the scalar contribution of
CMB anisotropies.We present the initial conditions for cosmological perturbations and the exact expressions
for the energy density and Lorentz force associated to the stochastic background of primordial magnetic elds,
given a power-law for their spectra cut at a damping scale.We then illustrate the scalar contribution to CMB
temperature and polarization spectra and compare it with the vector and tensor contributions.We conclude
by presenting the contribution of scalar uctuations sourced by such a stochastic background of primordial
magnetic elds to the bispectrum of CMB temperature anisotropies on large scales.
Cosmological signatures of primordial helical magnetic elds
Tina Kahniashvili,Carnegie Mellon University
Magnetic helicity plays an important role in astrophysics and cosmology.Magnetic helicity aects the formation
of observed magnetic elds in galaxies and clusters,changes the magnetic eld dynamics,and modies the gener-
ation of gravitational perturbations.Magnetic helicity imprints on the dynamics of gravitational perturbations,
and may leave some traces on Cosmic Microwave Background (CMB) anisotropies.
In this talk the eects induced by cosmological helical magnetic elds are discussed.There are dierent mech-
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anisms which can"seed"the generation of helical magnetic elds during the early Universe,i.e.in ation,pre-
and re-heating,the electroweak and QCD phase transitions.Generally speaking,the presence of primordial
magnetic helicity manifests the violationa of parity on the level of perturbations in the Universe,and thus,test-
ing cosmological magnetic helicity would open a new window to our understanding of the fundamental processes
in the early Universe.
The strength of magnetic helicity,and as a result,its detection prospects,strongly depend on the generation
mechanism of the associated magnetic eld.As a consequence,magnetic helicity generated during in ation
or phase transitions leave dierent"cosmological traces".We discuss here signatures of magnetic helicity on
CMB and on a relic gravitational wave background.In particular,a) Non-zero parity odd cross correlations of
CMB temperature and polarization anisotropies,such as temperature- B-mode polarization and E-mode and
B-mode polarization cross correlations,which are vanishing in standard cosmological models (which assume
the standard model of particles physics).b) Possible non-gaussianity of CMB uctuations induced by magnetic
helicity.c) Polarization of the relic gravitational waves background which can potentially be seen by space-based
interferometer missions,such as the Laser Interferometer Space Antenna (LISA).Detection prospects using the
current and upcoming cosmological observation data are brie y discussed.
1.4 Thursday June 4
Primordial magnetic elds and baryogenesis
Tanmay Vachaspati,Case Western Reserve University & Institute of Advanced Study
A connection is drawn between cosmic matter-genesis and helical primordial magnetic elds.The predicted
magnetic eld strength and coherence scale can be of cosmological interest.A number of important issues need
to be resolved to further develop this remarkable connection,which may prove invaluable to particle physics
and cosmology.
Magnetic eld production during preheating at the electroweak scale
Juan Garcia-Bellido,Universidad Autonoma de Madrid
In modern cosmology,the Big Bang corresponds to the moment of reheating of the universe after cosmic in ation,
when the energy density that drove the rapid expansion gets violently converted into relativistic matter and
radiation.Such a process is the arena for a very rich phenomenology,with explosive production of particles and
creation of topological defects,the production of a stochastic gravitational wave background,the possible origin
of the baryon asymmetry of the universe at the electroweak scale,as well as primordial magnetic elds.We
will show the mechanism behind the generation of helical magnetic elds during preheating in a model of low-
scale electroweak hybrid in ation,where inhomogeneities in the Higgs eld,resulting from tachyonic preheating
after in ation,seed the magnetic elds in a way analogous to that predicted by Vachaspati and Cornwall in
the context of the EW symmetry breaking.At this stage,the helical nature of the generated magnetic elds
is linked to the non-trivial winding of the Higgs-eld.We analyze non-perturbatively the evolution of these
helical seeds through the highly non-linear stages of symmetry breaking and beyond.Electroweak symmetry
breaking occurs via the nucleation and growth of Higgs bubbles which squeeze the magnetic elds into string-
like structures.The W-boson charge density clusters in lumps around the magnetic strings.After symmetry
breaking,a detailed analysis of the magnetic eld Fourier spectrum shows two well dierentiated components:
a UV radiation tail at a temperature T 0:23mH,slowly growing with time,and an IR peak associated to the
helical magnetic elds,which seems to follow inverse cascade,while both the amplitude and the correlation
length of the magnetic eld grow linearly with time.During this stage of evolution we also observe a power-law
growth in the helical susceptibility.These properties support the possibility that our scenario could provide the
seeds eventually evolving into the Gauss elds observed today in galaxies and clusters of galaxies.
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Primordial magnetic elds and gravitational waves
Chiara Caprini,CEA Saclay
The energy momentum tensor of a magnetic eld contains a tensor anisotropic stress component,which acts
as a source of tensor perturbations in the metric.Stochastic primordial magnetic elds contribute therefore to
the stochastic background of gravitational waves.This talk reviews the production of gravitational waves by
primordial magnetic elds,accounting for the eect of a non-zero helical component in the eld.The possibility
of detecting such gravitational waves both by direct measurements and in the CMB will be discussed,together
with the constraints on the magnetic eld amplitude that can be derived by imposing that the gravitational
wave background does not violate the Nucleosynthesis bound.
1.5 Friday June 5
Magnetic elds from cosmological perturbations
Keitaro Takahashi,Nagoya University
Detailed physical processes of magnetic eld generation from density uctuations in the pre-recombination era
are discussed.Solving Maxwell's equations and the generalized Ohm's law,the evolutions of the net charge
density,the electric current and the electromagnetic eld are solved.Unlike most of the previous works,we treat
electrons and photons as separate components under the assumption of tight coupling.We nd that generation
of the magnetic eld due to density uctuations takes place only in second order of both perturbation theory
and the tight coupling approximation.We also present some numerical results of the spectrum of magnetic
elds.
Evolution of magnetic eld spectra:fromthe very early universe,to recombination,to the present
Karsten Jedamzik,University of Montpellier
A detailed examination of the evolution of stochastic magnetic elds between high cosmic temperatures and
the present epoch is presented.A simple analytical model matching the results of the 3D MHD simulations
allows for the prediction of the present day magnetic eld correlation lengths and energy.Our conclusions
are multifold.(a) Initial primordial elds with only a small amount of helicity are evolving into maximally
helical elds.(b) There exists a correlation between the strength of the magnetic eld,B,at the peak of it's
spectrum and the location of the peak,given at the present epoch by:B  5 10
12
(L/kpc) Gauss,where
L is the correlation length determined by the initial magnetic eld.(c) Concerning studies of generation of
cosmic microwave background (CMBR) anisotropies due to primordial magnetic elds of B  10
9
Gauss on
 10 Mpc scales,such elds are not only impossible to generate in early causal magneto-genesis scenarios but
also seemingly ruled out by distortions of the CMBR spectrum due to magnetic eld dissipation on smaller
scales and the overproduction of cluster magnetic elds.(d) The most promising detection possibility of CMBR
distortions due to primordial magnetic elds may be on much smaller scales at higher multipoles` 10
6
where
the signal is predicted to be the strongest.(e) It seems possible that magnetic elds in clusters of galaxies
are entirely of primordial origin,without invoking dynamo amplication.Such elds would be of (pre-collapse)
strength 10
12
10
11
Gauss with correlation lengths in the kpc range,and would also exist in voids of galaxies.
Primordial magnetic elds:Origin and structure formation signals
Kandu Subramanian,Inter University Centre for Astronomy and Astrophysics
The generation of primordial large-scale magnetic elds in the early universe and their eects on structure
formation are discussed.Magnetic eld generation during say in ation requires one to break the conformal
invariance of the electromagnetic action.We outline one particular scenario for such generation.Primordial
magnetic elds also lead to a number of interesting eects on the evolution of the universe after recombination.
Their dissipation due to ambipolar diusion leads to ionization and heating of the intergalactic medium.They
induce density inhomogeneities and collapse of the rst dwarf galaxies at high redshifts.The extra electrons
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from magnetic eld dissipation help catalyse the formation of molecular hydrogen needed to cool the gas in
the rst structures.The reionization of the universe in the presence of primordial elds lead to distinctively
dierent signatures in the redshifted 21 cm line compared to standard models.We discuss how these structure
formation signals oer a sensitive probe of primordial magnetic elds.
2 Parallel sessions
2.1 Observations (Monday June 1)
Diuse radio emission in relaxed cool-core galaxy clusters
Federica Govoni,INAF - Osservatorio Astronomico Cagliari
I present results for sensitive observations to search for mini-halos in relaxed,cool-core galaxy clusters.We
investigate the radio properties of the new mini-halos in comparison with the radio properties of a representative
sample of mini-halos and halos already known in the literature.
The Coma cluster magnetic eld from Faraday Rotation Measures
Analisa Bonafede,Istituto di Radio Astronomia-INAF & Universita di Bologna
I will present a new ongoing study on the Coma cluster magnetic eld aimed at constraining its strength and
structure,and at reconciling dierent values found in the literature.At this scope we analyzed the polarization
properties of several sources in the Coma cluster eld recently observed at the Very Large Array at 3.6 and 6
cm for which Faraday Rotation Measures have been derived at the kpc scale.With the FARADAY code we
simulated random three dimensional magnetic eld models and by assuming a beta model for the thermal gas
distribution,we derived simulated Rotation Measure images.The comparison between simulated and observed
Rotation Measure images allows us to constrain the Coma cluster magnetic eld main properties.
Modeling magnetic elds in interacting galaxies
Marian Soida,Jagiellonian University,Astronomical Observatory
An attempt to explain polarized intensity observations of interacting spiral galaxies will be presented.The
model is based on kinematical N-body simulations of the ISM.The 3D velocity eld makes then an input to
MHD calculations.As the result synthetic polarized intensity maps are calculated and compared with real
observations.
The intergalactic medium of the galaxy cluster A665
Valentina Vacca,Universita degli Studi di Cagliari
The intergalactic medium of the galaxy cluster A665 is characterized by the presence of a faint synchrotron
diuse radio emission extended over 1Mpc (radio halo).In this talk I will present a study of the radio halo
brightness uctuations in order to determine,in comparison with simulated images,the magnetic eld power
spectrum.
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Radio Polarimetry and Magnetic Fields in Distant Galaxies
Christopher A.Hales,The University of Sydney & CSIRO ATNF
Co-Authors:Bryan M.Gaensler The University of Sydney,Ray P.Norris CSIRO ATNF,Enno Middelberg
Ruhr-Universitat Bochum
The origin and evolution of large scale magnetic elds in the Universe remain poorly constrained by observational
data.In an eort to address this,we are using the Australia Telescope Large Area Survey (ATLAS) to investigate
magnetic elds in an ensemble of radio galaxies that extend to beyond z  2.We present deep polarimetric
ATLAS observations at 1420MHz over seven square degrees,to a minimum rms noise level of  18Jansky per
beam in stokes Q and U.We explore statistics of the polarised sky as a function of parameters such as redshift,
ux,and angular size,comparing the results from separate survey elds.This will form part of a longer-term
project to measure the magnetic power spectrum of the intergalactic medium
Measuring magnetic power spectra
Petr Kuchar,Max-Planck-Institute for Astrophysics,Garching
The magnetic power spectra of turbulent astrophysical plasma is a key to understand their dynamical properties.
It is imprinted into Faraday rotation maps and therefore can be measured.We present the latest development
on the technique of Faraday rotation based magnetic power estimations and our results of such measurements.
In particular,we estimate the spectral index of the inertia range of the turbulent cascade in the Hydra A cool
core region.
2.2 Primordial magnetic elds (Monday June 1)
Interactions of cosmological gravitational waves and magnetic elds
Elisa Fenu,University of Geneva
The energy momentum tensor of a magnetic eld always contains a spin-2 component in its anisotropic stress
and therefore generates gravitational waves.It has been argued in the literature that this gravitational wave
production can be very strong and that back-reaction cannot be neglected.On the other hand,a gravitational
wave background does aect the evolution of magnetic elds.It has also been argued that this can lead to a
very strong amplication of a primordial magnetic eld.In this talk I will revisit these claims and study back
reaction to second order.
Higher-dimensional Hall eect,and cosmological magnetic elds
Juerg Froehlich,ETH-Zurich
I review the theory of higher-dimensional Hall eects and outline how they might give rise to a mechanism
explaining the growth of primordial magnetic elds in the early universe.The mechanism in question involves
an axion that emerges naturally from the theory of higher-dimensional Hall eects.It is shown that the time
derivative of the axion can be interpreted in terms of a space-time dependent chemical potential conjugate to
the pseudo-scalar fermion density.
Magnetic Fields in Radiation Era
Lukas Hollenstein,Institute of Cosmology & Gravitation,University of Portsmouth
I review the generation and evolution of large scale magnetic elds during radiation era.Particularly,I analyse
the possibility that topological defects can act as a source of magnetic elds through the Harrison mechanism.It
is shown that it is only ecient for temperatures above T  0:2 keV.The main result is that the vector metric
perturbations generated by the defects cannot induce vorticity in the matter uids at linear order,thereby
excluding the production of currents and magnetic elds.We show that anisotropic stress in the matter and/or
9
radiation uids is required to source vorticity and magnetic elds.
Helical magnetic eld in electroweak baryongenesis
Yifung Ng,Case Western Reserve Univerisity
We study the creation of primordial helical magnetic eld via sphaleron decays during a rst order phase
transition.
Generation of magnetic elds and vorticity in the presence of photon anisotropic stress
Roy Maartens,Portsmouth University
I will describe the General Relativistic equations that govern the generation of magnetic elds and vorticity at
nonlinear order in the cosmic plasma before recombination,taking into account the eect of photon anisotropic
stress.I will discuss some of the qualitative features of these equations.
2.3 Numerical methods (Tuesday June 2)
Radio Haloes from Secondary CR Models in cosmological MHD simulations
Julius Donnert,Max Planck Institut fur Astrophysik,Garching
To test models for the origin of magnetic elds in galaxy clusters we are using cosmological MHD simulations,
coupled with a semi-analytic model for magnetic elds in galactic out ows from star-bursting dwarf galaxies
as magnetic seed elds.Such models reproduce the observed magnetic eld strengths in galaxy clusters at low
redshift and make predictions for the magnetic elds in laments,which can be compared with predictions from
cosmological (e.g.primordial) seed elds.This allows us to put constraints on the presence of cosmic ray protons
in galaxy clusters by comparing in detail the induced radio emission in these simulations with observations.
Investigating a simulated Coma like cluster allows us further to clarify the role of the SZ-decrement on the
spectral shape of the observed radio emission of the Coma cluster.
Towards Simulating Cool Core Clusters
Federico Stasyszyn,Max Planck Institut fur Astrophysik,Garching
Using Smoothed Particle Magneto Hydrodynamics (SPHMHD) in Gadget,we study the eects magnetic elds
in galaxy clusters.We implemented several regularization schemes for the magnetic eld.We study the
robustness of our results against artifacts from numerical non vanishing magnetic eld divergence applying
divergence cleaning schemes.We run high resolution cosmological simulations of cluster formation in order to
evaluate our implementation in a realistic scenario.The rst results are encouraging and the eciency of our
code allows us to push for the rst time the resolution of the simulations down to 1kpc/h within the cores of
galaxy clusters.Resolving the turbulence and therefore the magnetic eld amplication on such small scales,
which are below the smallest scales of magnetic elds observed in galaxy clusters,allows us to investigate the
role of viscosity and magnetic dissipation within the ICM.I will also present preliminary results from including
additional physics such as star formation and radiative cooling showing that the magnetic eld undergoes further
amplication within the cool core region of galaxy clusters and might be able to get comparable to the thermal
pressure.
Turbulence in Galaxy Clusters simulated with a new AMR scheme
Franco Vazza,Radio Astronomy Institute(Bologna),Astronomy Department (Bologna)
I will present recent results for the characterization of turbulent motions in the ICM of a sample of simulated
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Galaxy Clusters,as produced by a novel implementation of Adaptive Mesh Renment in the ENZO code.This
scheme allows for unprecedented spatial resolution at shocks and turbulent features of the ICM,even at large
(> 2Mpc) distances from the clusters center,dierent from SPH or standard AMR simulations.I will present
measures of the turbulent energy budget inside clusters and discuss the evolution of their velocity power spectra.
Generation of Seed Magnetic Fields with Biermann Mechanism in Primordial Supernova Rem-
nant
Hidekazu Hanayama,Department of Astronomy,University of Tokyo
Although magnetic elds of  G are observed in many galaxies,the origin of the elds is still not clear.
The amplication mechanism such as galactic dynamos is suggested to explain the observed magnetic elds.
However,seed magnetic elds are initially required to be amplied by the dynamos.Various origins for the seed
elds are proposed but there is no consensus.There is a remarkable astrophysical process for the generation
of the magnetic elds which depends on the vorticity produced by the gradients of the electron pressure and
the density of the plasma,the so-called Biermann mechanism (Biermann 1950).The Biermann mechanism
produces magnetic elds in a turbulent gas,even if the elds is absent initially.The process is expected to
work in supernova remnants (SNR) of rst-generation stars,when the motion of the shocked gas is dominated
by turbulent ow.In this study,we focus on the generation process of magnetic elds in primordial SNR and
perform a series of two-dimensional magneto-hydrodynamical simulations taking account the Biermann eect.
Especially,since (i)the Biermann mechanism depends on the electron pressure (or temperature) and (ii)the
electron temperature is not equilibrated to the ion temperature in the early adiabatic expansion phase (Itoh
1978),we incorporate the relaxation process of electron and ion temperatures with the Coulomb interaction
and calculate the magnetic elds with the electron pressure in the region where the equilibrium is suciently
achieved,assuming an isothermal state in unequilibrated regions.For the model of the surroundings of SNR,
we assume a density inhomogeneity which is expected for ionized regions around the supernova.We calculate
various models with dierent parameters for (1)the scale and the amplitude of the density inhomogeneity,(2)the
average density of interstellar medium (ISM),and (3)the supernova explosion energy.As a result,we nd that
magnetic elds of 10
17
-10
18
G with a coherence length of 60{120 pc are generated in the adiabatic expansion
phase.The total magnetic energy attains 10
25
-10
26
ergs per SNR.The magnitude and total energy of the
magnetic elds are positively correlated with the amplitude of the density inhomogeneity and the supernova
explosion energy.On the other hand,they are negatively correlated with the average density of ISM and the
scale length of the density uctuation.The coherence length of the magnetic elds depends on the scale length of
the uctuation.Moreover,using the Sedov solution,we nd an empirical law which explains the magnitude and
total energy of the generated magnetic elds,in good agreement with our numerical results.The average energy
density of the magnetic elds is estimated to be 10
42
erg cm
3
,and it might be amplied to 10
39
erg cm
3
in protogalaxies which corresponds to 10
19
G.This is sucient for the seed elds required for the galactic
dynamo mechanism.
Gamma-ray induced cascades and magnetic elds in intergalactic medium
Andrii Neronov,CERN
I will present the results of Monte-Carlo simulations of three-dimensional electromagnetic cascade initiated by
interactions of multi-TeV gamma rays with the cosmological infrared/optical photon background in the inter-
galactic medium.Secondary electrons in the cascade are de ected by intergalactic magnetic elds before they
scatter on CMB photons.This leads to extended 0.1-10 degree scale emission around extragalactic sources of
very-high-energy gamma rays.The morphology of the extended emission depends,in general,on the properties
of the magnetic elds in the intergalactic medium.Using Monte-Carlo simulated data sets,we demonstrate
that the decrease of the size of extended source with the increase of energy allows to measure weak magnetic
elds with magnitudes in the range from < 10
16
G < 10
12
G if they exist in the voids of the Large Scale
Structure.
Galaxy Cluster:Magnetized,Cosmic Lighthouses
Klaus Dolag,Max Planck Institut fur Astrophysik,Garching
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Clusters of galaxies are ideal cosmological probes.They are the largest collapsed objects in the Universe
and therefore are very sensitive to the structure formation process.Cosmological simulations are a valuable
probe of our understanding and harbor enormous potential for the interpretation of observational data.Such
simulations are extremely challenging,as the structures in and around clusters span a very large dynamic range
in scales.Furthermore,the complexity of the intra-cluster medium revealed by multi-frequency observations
demonstrates that a variety of physical processes are in action and must be included to produce accurate and
realistic models.I will highlight some dierent aspects of numerical studies which aim to understand some of
the physical processes at work,as well as to probe the cosmological context.
2.4 Cosmic magnetic elds and the CMB (Tuesday June 2)
Constraints on the Primordial Magnetic Field and Neutrino Mass from the CMB Polarization
and Power Spectra
Mathews Grant,University of Notre Dame
Magnetic elds play an important role in many astronomical phenomena on various cosmological scales.In
particular,a primordial magnetic eld (PMF) could manifest itself in the cosmic microwave background (CMB)
temperature and polarization anisotropies,and also in the formation of large- scale structure.We have devel-
oped a new high-precision theoretical framework in which to calculate the CMB temperature and polarization
anisotropies,along with the matter power spectrum generated when a power-law PMF is present at the epoch
of photon last-scattering.We discuss preliminary evidence that the existing accumulated data on both the
matter and CMB power spectra on small angular scales xes both the upper and lower limits to the magnetic
eld strength and power spectral index.We nd parameter values for the amplitude of the PMF of 2:248nG
< B < 3:055nG and a spectral index in the range 2:387 < n < 1:367 at the present scale of 1 Mpc.This may
be the rst direct evidence that a primordial magnetic eld was indeed present during the big bang.We also
show that this nite magnetic eld can be used to determine an independent constraint on the sum of neutrino
masses from its eect on the CMB polarization.
CMB Constraints on Inhomogeneous Primordial Magnetic Fields
Daniela Paoletti,Universita degli studi di Ferrara,INAF/IASF Bologna,INFN Ferrara
We investigate the full contribution of a stochastic background of primordial magnetic elds (PMF) on cosmic
microwave background (CMB) anisotropies in temperature and polarization and use the current CMB data
to constrain the parameters characterizing the PMF.By considering the relevant contributions from PMF we
perform a Markov Chain Monte Carlo with the currently available CMB data and we present the constraints
on the spectral index and amplitude of the PMF.
Wide-Angle CMB Fluctuations and Edge-of-the-Universe Magnetic Fields
Herbert M.Fried,Brown University
Could the weak (10
9
Gauss) magnetic elds observed at the limits of the visible universe have been originally
produced at the instant of the Big Bang,weakened during the many-fold expansion of the universe,but retained
enough directional asymmetry to account for the apparent wide-angle CMB uctuations?A simple model will
be presented.
Alfven turbulence in the WMAP 5 year data and a forecast for the PLANCK
Jaiseung Kim,Niels Bohr Institute
We have investigated imprints of cosmological Alfven waves in Cosmic Microwave Background(CMB) anisotropy.
For data constraints,we have used the power spectrum of the recent CMB observations,and correlations esti-
mated from WMAP Internal Linear Combination (ILC) maps.Our analysis shows 3 evidence of cosmological
12
Alfven waves.Using the 3 limit from our analysis and the Alfven velocity limit from the total energy density
constraint,we impose a lower bound on the amplitude of primordial vector perturbation:A
v
& 5  10
4
at
k
0
= 0:002=Mpc.
2.5 Magnetic elds and structure formation (Thursday June 4)
A string cosmological model of Bianchi type-I in the presence of a magnetic eld
Mihai Visinescu,Institute for Physics and Nuclear Engineering,Bucharest
Einstein's eld equations are considered in the presence of a cosmological string and magnetic eld for Bianchi
type-I space-times.Some exact solutions are produced using a fewplausible assumptions regarding the parametriza-
tion of the cosmic string and magneto- uid.The analytical solutions are supplemented with numerical evalua-
tions.
The role of primordial magnetic elds during the reionization epoch and their eects on the
formation of the rst stars
Dominik Schleicher,Zentrum fuer Astronomie der Universitat Heidelberg
We discuss the role of primordial magnetic elds during the reionization epoch and their eects on the formation
of the rst stars.Such eects may include changes in the dynamics caused by the direct in uence of the magnetic
eld,or by the additional heat input into the gas due to ambipolar diusion.
We present self-consistent calculations of the chemical evolution of primordial gas in the presence of primordial
magnetic elds on scales ranging from that of the intergalactic medium down to that of protostellar collapse.
We nd that the eects on the chemistry are signicant for comoving eld strengths of at least 0.1 nG,as
expected from some models of magnetogenesis in the early Universe.Requiring that reionization produces the
observed Thomson scattering optical depth leads to an upper limit of 3 nG on the primordial eld strength.
We show that magnetic elds with comoving eld strengths of 0.1 nG or more have a strong impact on the
dynamics of primordial protostellar collapse,due to a combination of both thermal and magnetic eects,and
we discuss the conditions under which star formation in the rst minihalos is suppressed.Even for magnetic
eld strengths that are orders of magnitude smaller than this critical value,there is the possibility that elds
are amplied during the collapse phase to reach eld strengths sucient to drive protostellar out ows,which
will magnetize the IGM and aect subsequent generations of stars.On the scale of the protostellar disk,they
are likely sucient to trigger the magnetorotational instability and will govern accretion on the protostellar
core.
Galactic dynamos against conservation laws
Axel Brandenburg,Nordita
In the kinematic regime,when the magnetic energy is weak compared with the kinetic energy of the motions
(turbulence),magnetic elds tend to be generated predominantly on the resistive scale.This happens on the
turnover timescale of the turbulence at that scale and is thus a fast process.Soon the eld saturates at that
scale and begins to occupy all larger scales up to the energy-carrying scale of the turbulent motions.This is
true both for the so-called small-scale and large-scale dynamos.Large-scale dynamos are of particular interest,
because they are believed to be responsible for the grand design of galactic magnetic elds.Simulations in the
contexts of spherical and disc-like astrophysical bodies have shown that this process can also be fast provided
the dynamo can dispose of magnetic helicity at scales smaller than that of the large-scale magnetic eld.In
this talk I will focus on comparisons between advanced mean-eld models and simulations.
Cosmic magnetism and large-scale geometry
13
Christos Tsagas,University of Thessaloniki
Magnetic elds are the only large-scale matter source known in the universe today.In the geometrical framework
of general relativity,vector sources have a special status.Vector sources interact with the spacetime curvature
not only through Einstein's equations but also via the Ricci identities.In the case of magnetic elds,the result
of this interaction depends on their physical properties,of which their tension seems to play a prominent role.
We discuss aspects of the gravito-magnetic coupling and how it may aect the Maxwell eld as well as the
geometry of the space in which it is embedded.
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