Interstellar Broadening of Compact Low Galactic Latitude Radio Sources

Abstract

Scattering of radio waves off inhomogeneities in electron density in the interstellar medium can produce an apparent broadening in the angular diameter of an intrinsically compact background radio source. The magnitude and distribution of this effect at low galactic latitudes (|b|<5°) is not well known, although several cases suggest substantial broadening in certain directions, such as the Cygnus X region (Anderson et al. 1972), and the galactic center (Davies, Walsh, and Booth 1976). Large scattering in the plane is consistent with the scintillation properties of pulsars seen through substantial thicknesses (≳ 1 kpc) of the galactic disk.