We present low frequency observations at $315$ and $745$ MHz from the upgraded Giant Metrewave Radio Telescope (uGMRT) of the edge-on, near-by galaxy NGC 4631. We compare the observed surface brightness profiles along the minor axis of the galaxy with those obtained from hydrodynamical simulations of galactic outflows. We detect a plateau in the emission at a height of $2-3$ kpc from the mid-plane of the galaxy, in qualitative agreement with that expected from simulations. This plateau is believed to be due to the compression of magnetic fields behind the outer shocks of galactic outflows. The estimated scale height for the synchrotron radio emission of $sim 1$ kpc indicates that cosmic ray diffusion plays as much an important role in forming the radio halo as does the advection due to the outflows. The spectral index image with regions of flatter radio spectral index in the halo appears to indicate possible effects of gas outflow from the plane of the galaxy.
Download