Radio halos of star forming galaxies
  We study the synchrotron radio emission from extra-planar regions of star
forming galaxies. We use ideal magneto-hydrodynamical (MHD) simulations of a
rotating Milky Way-type disk galaxy with distributed star formation sites for
three star formation rates (SFRs) (0.3, 3, 30 M$_{\odot}$ yr$^{-1}$). From our
simulations, we see emergence of galactic-scale magnetised outflows, carrying
gas from the disk. We compare the morphology of the outflowing gas with
hydrodynamic (HD) simulations. We look at the spatial distribution of magnetic
field in the outflows. Assuming that a certain fraction of gas energy density
is converted into cosmic ray energy density, and using information about the
magnetic field, we obtain synchrotron emissivity throughout the simulation
domain. We generate the surface brightness maps at a frequency of 1.4 GHz. The
outflows are more extended in the vertical direction than radial and hence have
an oblate shape. We further find that the matter right behind the outer shock,
shines brighter in these maps than that above or below. To understand whether
this feature can be observed, we produce vertical intensity profiles. We
convolve the vertical intensity profile with the typical beam sizes of radio
telescopes, for a galaxy located at 10 Mpc (similar to NGC 891) in order to
estimate the radio scale height to compare with observations. We find that for
our SFRs this feature will lie below the RMS noise limit of instruments. The
radio scale height is found to be $\sim 300-1200$ pc , depending on the
resolution of the telescope. We relate the advection speed of the outer shock
with the surface density of star formation as $\rm{v}_{\rm adv} \propto
\Sigma_{\rm SFR}^{0.3}$ which is consistent with earlier observations and
analytical estimates.
