Post on 31-Dec-2015
description
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?