Radio continuum observations of the edge-on spiral galaxy NGC 4666

Radio continuum emission from the edge-on spiral galaxy NGC 4666 has been studied using high-resolution observations at 327 MHz with the Ooty Synthesis Radio Telescope (OSRT) and at 1465 and 4885 MHz with the VLA. Radio emission has been detected from the disc of the galaxy as well as from the halo up to a distance of ∼7kpc from the galactic plane. The radio spectral index between 327 and 1465 MHz remains almost constant (α=0.60) with height to a distance of ∼5kpc above the plane of the galaxy. Beyond this distance, the spectrum steepens rapidly. The galaxy has also been observed at 4750 MHz with the Effelsberg 100-m telescope and the spectrum of the integrated flux density is derived. The total intensity spectrum and the variation of the radio spectral index between 327 and 1465 MHz are examined in the context of simple propagation models for the relativistic electrons which diffuse and/or convect from the galactic disc into the halo. The recent theoretical studies of transport mechanisms utilizing extended source functions, variable diffusion coefficient and convection (dynamical halo) are discussed. The present results are broadly consistent with all these models.