Ram pressure effects in the galactic plane and galactic dynamos in the
  no-z approximation
  The magnetic field of galaxies is believed to be produced by internal dynamo
action, but can be affected by motion of the galaxy through the surrounding
medium. Observations of polarized radio emission of galaxies located in galaxy
clusters have revealed noticeable features of large-scale magnetic
configurations, including displacements of the magnetic structures from the
optical images and tails, which are possible imprints of ram pressure effects
arising from motion of the galaxies through the intracluster medium. We present
a quantitative dynamo model which attempts to describe the above effects. In
contrast to the traditional problem of a wind affecting a body with a
prescribed magnetic field, we investigate how a non-magnetized wind flow
affects a magnetic field that is being self-excited by galactic dynamo action.
In order to isolate the leading physical effects we exploit a simple dynamo
model that can describe relevant effects. In particular, we use what is known
as the 'no-z' approximation for the mean-field dynamo equations. In a suitable
parametric range we obtain displacements of the large-scale magnetic field, as
well as magnetic tails. However, the specific details of their locations are
quite counterintuitive. The direction of displacement is perpendicular to,
rather than parallel to, the wind direction. The point at which the tail
emerges from the galaxy depends on details of the model. The tail is eventually
directed downstream. In the simplest case the magnetic tail begins in the
region where the wind decreases the total gas velocity. Any wind that
penetrates the galaxy modifies the intrinsic dynamo action. These features are
different from those found in ram-pressure models. Any determination of
galactic motion through the cluster medium from observational data needs to
take the effects of dynamo action into account.
