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Study of Cosmic Magnetic Fields with Square Kilometer Array

Study of Cosmic Magnetic Fields with Square Kilometer Array. Keitaro Takahashi Nagoya University 4/Nov./2010 @Japan-SKA workshop 2010. “Cosmic Magnetic Fields”. sub Science Working Group on “Cosmic Magnetic Fields” 11 researchers from 9 institutes

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Study of Cosmic Magnetic Fields with Square Kilometer Array

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  1. Study of Cosmic Magnetic Fields with Square Kilometer Array Keitaro Takahashi Nagoya University 4/Nov./2010 @Japan-SKA workshop 2010

  2. “Cosmic Magnetic Fields” sub Science Working Group on “Cosmic Magnetic Fields” 11 researchers from 9 institutes Keitaro Takahashi (Nagoya): chair Takuya Akahori (Chungnam National University) Hidekazu Hanayama (NAOJ), Kiyotomo Ichiki (Nagoya) Makoto Inoue (ASIAA), Susumu Inoue (Kyoto) Takahiro Kudoh (NAOJ), Mami Machida (Kyusyu) Hiroyuki Nakanishi (Kagoshima) Yoshiaki Sofue (Meisei), Hajime Susa (Konan) Method: theory, numerical simulation Target: galaxy, cluster of galaxies, cosmology

  3. Introduction: Origin of Cosmic Magnetic Fields

  4. Origin of Magnetic Fields Origin of magnetic fields of the earth is one of the greatest mystery in modern physics. We now know various astronomical objects have their own magnetic fields.

  5. ubiquitous magnetic fields neutron star 12 10 G 9 10 G white dwarf active galactic nuclei 6 10 G 3 10 G Sun 1 G Earth cluster of galaxies 1mG SNR -6 10 G galaxy cosmological 1nG 6 1km 10 km 1pc 1kpc 1Mpc size

  6. 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

  7. Observation of Cosmic Magnetic Fields and Importance of Wideband Observation

  8. Observation of Magnetic Fields 1. synchrotron radiation 2. Faraday rotation polarization angle rotation measure radio pulsar B1154-62 integral from the source to the observer Information on B can be obtained from the slope.

  9. sources Application We can probe target’s magnetic fields by observing a lot of sources behind the target. 292 sources behind LMC target observer Gaensler et al., 2005

  10. Importance of Wideband So far, rotation measures have often been determined by very narrow band observations (1.365 – 1.435GHz). => very large error Wideband observation is important for precise determination of rotation measure. polarization angle (degree) wavelength^2 (cm^2)

  11. Importance of Wideband source The situation is more complicated in general. - emission of target itself - galactic foreground target polarization degree mixture of radio wave from source and target itself (and possible galactic foreground) polarization angle Brentjens & de Bruyn, 2005

  12. Importance of Wideband Faraday rotation measure synthesis, (Burn, 1966) polarized surface brightness F(φ): Faraday dispersion function Faraday depth (~ “distance”) polarization degree F(φ) represents which part is emitting and where and how much magnetic fields exist. F(φ) can be obtained by inverse “Fourier transformation”. polarization angle Wideband observation is crucial to probe magnetic fields. Brentjens & de Bruyn, 2005

  13. Activity of Our Group

  14. Galaxy ring & vertical fields (Berkhuijsen et al., 2003) M31 (Andromeda galaxy) • global structure • ring • axisymmetric • bisymmetric • vertical • How were these formed?

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

  16. Galaxy Cluster and Large Scale Structure -6 cluster of galaxies: ~10 G collection of 10-1000 galaxies large scale structure: ??? filament, void SDSS

  17. Galaxy Cluster and Large Scale Structure Cosmological simulation of large scale structure (Ryu et al., 2008, Akahori & Ryu, 2010) Primordial magnetic fields evolve through structure formation. rotation measure so small for the present telescope but observable by SKA magnetic fields associated with large scale structure Talk by Akahori-san

  18. Reionization • magnetogenesis at reionization • (Ando, Susa et al., 2010) • - UV and X-ray from first stars • momentum transfer from • radiation to electrons • inhomogeneous ISM • leads to rotational electric current • => magnetic field generation

  19. Reionization Magnetic fields are generated behind the cloud. Upto 10 Gauss for reasonable situations. -20 B(G)

  20. Cosmological generation of cosmological magnetic fields in the early universe (KT, Ichiki et al., 2005, 2006, 2007, 2008) tiny density fluctuations in the early universe => electrons are stripped from protons by radiation pressure => electric current, electric fields => magnetic field generation

  21. Cosmological Spectrum at recombination -14 cutoff ～ 10 G -14 -18 -22 log B(G) at recombination -26 -25 horizon scale ～ 10 G -30 z = 10 B = 10 G can seed galactic fields. -18 -34 -38 1Gpc 1Mpc 1kpc 1pc comoving scale

  22. Grand Scenario • primordial magnetic fields • density fluctuations • - reionization • wideband observation • Faraday rotation • synchrotron large-scale structure - cluster of galaxies - filament galactic fields

  23. Review Paper “Unsolved Problems on Cosmic Magnetic Fields” 1. Introduction (K. Takahashi) 2. Observation of Magnetic Fields (K. Takahashi) 3. Cosmology (K. Takahashi, K. Ichiki) 4. Cluster of Galaxies and Large Scale Structure (T. Akahori) 5. Galaxy (T. Kudoh) 6. AGN and Jet (M. Machida) 7. Conclusion (K. Takahashi) Currently Japanese (54pages) English version will appear soon.

  24. 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 END

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