Seeding the ICM: Primordial or Astrophysical? Jungyeon Cho Chungnam National University, Korea Cho & Yoo (2012; ApJ) Cho (2013; PRD) Cho (2014, ApJ) Origin of Magnetic fields in the ICM  If Spitzer viscosity, it’s astrophysical!

Nearby Galaxies (2MASS) B in the large-scale structure of the universe? Observations: ~  G in clusters ~nG in filaments???  Turbulence can amplify magnetic fields

Origin of cosmic seed magnetic fields is uncertain Primordial? Astrophysical? B from the early universe? Battery effects during the large-scale structure formation? (jets, winds, stripped gases, …)

Viscosity in the ICM: Spitzer or not? Spitzer viscosity ~ l mfp v th In the ICM, the mean free path can be > kpc. e.g.) l pp > 10kpc, l ee > 1kpc  Viscosity can be large  Reynolds number  100  Turbulence dynamo is inefficient! *Efficiency of turbulence dynamo depends on viscosity

If Spitzer, dynamo is NOT efficient t B2B2 Saturation t univ  Strength of B matters! B seed ~ G (primordial) ~10 -9 G (astrophysical) B seed ~ G (primordial) ~ G (astrophysical)

Simulation results (for Spitzer ) B max t un i v G G G t un i v G G

Expectations for Spitzer viscosity  Turbulence dynamo is inefficient  Strength of the seed field matters  Primordial B should be stronger than G  It’s close to the upper limit of G cf) Dr.Trivedi’s talk, Dr. Kobayashi’s talk  Astrophysical B should stronger than G  It may be easy to satisfy the condition!  Therefore, if the Spitzer viscosity is correct, primordial seed B may not be the origin!

If viscosity  0 (or Re   ) for some reason,… t B2B2 Astrophysical Growth rate=linear Saturation Primordial  Initial conditions are wiped out! t univ < 2x10 9 years  It’s difficult to know the origin

Astrophysical seed fields need homogenization  Homogenization is in general fast! Homogenization time ~ L sys /V This is a general result  It does not depend on viscosity

Expectations for viscosity  0  Turbulence dynamo is so efficient that strength and shape of the seed field doesn’t matter  It is difficult to tell the origin!  Both primordial and astrophysical seed fields can produce B of order O(  G) in the ICM  Note: For a typical cluster, B saturation  10  G  For a cluster with size 1 Mpc, homogenization time 75 km/sec.

Conclusions B in the ICM: Primordial or Astrophysical? in the ICM: Spitzer or Not? ~ Spitzer B in the ICM =Astrophysical! << Spitzer B in the ICM =?