Cosmological Seed Fields versus Seed Fields Generated in Protogalaxies

Dmitry SokoloffMoscow State University

Moscow, Russiain collaboration

with D.Mossand V.Semikoz

Galactic Magnetism –Perspectives of Observation and Modeling

May 16 - 20, 2011Pushchino, Moscow region, Russia

Br BT

Ω

Differential rotation

BT Br

α

Helicity

GALACTIC DYNAMO

Basic mechanism

The excitation mechanism requires a seed magnetic field.Two options: 1. Magnetic field is created in after recombination

2. A cosmological seed field

How to decide which option is better?

A standard approach: formulate scenarios for both cases, isolate specific features and try to confront them with observations

A scenario for magnetic fields created after recombination: talks of Moss, Arshakian, …

Seeds in protogalaxies + conventional mean-field dynamo

Spatial configurations

Cosmological seeds (a standard viewpoint)

Homogeneous magnetic field.Do not destroy isotropy provided is weak

enough (< 1011G is more then sufficient).Still can be strong enough to be a seed

Homogeneous relic field+ dynamo: it works unexpectedly bad (simulations of D.Moss)

Rotation expels homogeneous field on the remote part of the galaxy(simulations of D.Moss)

A cosmological magnetic field is useful to explain the baryon asymmetrySemikoz, Sokoloff, Valle,PRD 2009

We can not distinguish between

Small-scale cosmological seed + dynamo

A battery mechanism + small scale dynamo + mean-field dynamo

A large-scale seed + small-scale dynamo +

Mean-field dynamo

What says cosmology?

1. Everything is known (this statement persists)

Nothing about homogeneous magnetic field

This idea looked strange 10 years agoIt looks attractive todayMy interpretation: the topic is completely

obscure

A possibility to go further

Neronov and D.Semikoz:Magnetic fields between galactic clusters(10-15 G)Faraday rotation?Small-scale or large-scale fields?