Study ofCosmic Magnetic Fields
with Square Kilometer Array
Keitaro Takahashi
Nagoya University
Sep/24/2010 @AP-RASC 2010

Origin of Magnetic Fields
Origin of magnetic fieldsof the earth is one of
the greatest mysteryin modern physics.

We now know various astronomical objects havetheir own magnetic fields.

ubiquitous magnetic fields

neutronstar

1210 G
910 G

whitedwarf

610 G

activegalacticnuclei

310 G

Sun

1G

Earth1mG

cluster ofgalaxies

SNR-610 G

galaxy cosmological

1nG

1km

610 km

1pc

1kpc

1Mpc

sizeOrigin of Magnetic Fields (Extended)

Extended Einstein’s Question
1. Earth => astronomical object- galaxies- clusters of galaxies
2. cosmological fields?
- magnetic fields not associated with any objects- only an upper bound ~ 0.1nG

Observation of Magnetic Fields
1. synchrotron radiation
2. Faraday rotation
polarization angle

rotation measureintegrationfrom the source
to the observer
Information on B
can be obtained
from the slope.

radio pulsar B1154-62

Application

sources

We can probe target’s magnetic
fields by observing a lot of sourcesbehind the target.
292 sources behind LMC

targetobserverGaensler et al., Science (2005)

Importance of Wideband

Wideband observation isimportant for precise
determination ofrotation measure.

polarization angle (degree)

Rotation measures have often been determined byvery narrow band observations (1.365 – 1.435GHz).
=> very large error

wavelength^2 (cm^2)

Importance of Wideband
The situation is more complicatedin general.
-emission of target itself-emission of our galaxy

sourcetargetpolarization degree

polarization angle

Brentjens & de Bruyn, A&A (2005)

mixture of radio
wave from source
and target itself
Wideband observation is
crucial to probe magnetic fields.

SKA-Japan Consortium
Engineering Working Group
Science Working Group“AGN”, “Astrometry”, “Pulsar”“Galaxy Evolution”, “Spectral Line Survey”“Cosmic Magnetic Fields”
11 researchers from 9 institutes
Keitaro Takahashi (Nagoya University)
Takuya Akahori (Chungnam National University)
Hidekazu Hanayama (NAOJ), Kiyotomo Ichiki (Nagoya University)
Makoto Inoue (ASIAA), Susumu Inoue (Kyoto University)
Takahiro Kudoh (NAOJ), Mami Machida (Kyusyu University)
Hiroyuki Nakanishi (Kagoshima University)
Yoshiaki Sofue (Meisei University), Hajime Susa (Konan University)

Method: theory, numerical simulation
Target: galaxy, cluster of galaxies, cosmology

Galaxy
M31 (Andromeda galaxy)global structure- ring- axisymmetric- bisymmetric- vertical
How were these formed?

ring & vertical fields (Berkhuijsen et al. 2003)

Galaxy
primordial origin (Sofue, Kudoh & Machida, 2010)
example: bisymmetric field-uniform field at galaxy formation-winding up with rotating disk
confirmation by numerical simulations

Galaxy Cluster and Large Scale Structure
cluster of galaxies: ~10 -6 Gcollection of 10-1000 galaxies
large scale structure: ???
filament, voidSDSS

Galaxy Cluster and Large Scale Structure
MHD simulation of large scale structure(Ryu et al., 2008, Akahori & Ryu, 2010)
Primordial magnetic fields evolve through structure formation.
magnetic fields associatedwith large scale structure

rotation measureso small for the present telescope
but observable by SKA

Cosmological
generation of cosmological magnetic fields in the early universe(KT et al., 2005, 2006, 2007, 2008)
tiny density fluctuations in the early universe=> anisotropy of cosmic microwave background radiation
cosmological magnetic fields

Summary
Origin of cosmic magnetic fields-mystery in modern astrophysics-stars, galaxies, clusters of galaxies, universe itself-wideband is crucial for measurement through Faraday rotation-SKA-Japan consortium Science Working Group“Cosmic Magnetic Fields”-theory, numerical simulation-galaxy, cluster of galaxies, cosmology

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