Faraday rotation signatures of fluctuation dynamos in young galaxies

Freitag, 7. September 2018, 11:00 - 12:30
Veranstaltungsort* Library
Faraday rotation signatures of fluctuation dynamos in young galaxies

Abstract :

Over the course of the last decade, Mg II absorption systems probed by a
number of authors has revealed the existence of magnetic fields in young
galaxies out to redshifts $z sim 1$, that are of comparable strengths to
those observed in galaxies of today. The discovery of such strong fields
has sparked critical questions regarding their generation mechanism and
their degree of coherence. Addressing these questions form the subject of
discussion of this talk. Drawing from the rich body of work on turbulent
dynamos, we argue that such strong fields can plausibly arise from fluctuation
dynamo action. It is then natural to ask, if the dynamo generated fields
are coherent enough and the extent to which the Faraday rotation measure
(RM) obtained from such fields compares with the observational estimates
from Mg II absorption systems. Aided by numerical simulations, we show
that the obtained rms values of Faraday RM at dynamo saturation is about
$45 - 55%$ of the value expected in a model where fields are assumed to
be coherent on the forcing scale of turbulence. This leads to a random RM
of $16 - 48,{rm rad,m^{-2}}$, consistent with observations. We conclude
with a discussion of the resulting implications along with an outline of
future research directions.

: Sharanya Sur, Indian Institue of Astrophysics