The radio emission from the Galaxy at 22 MHz

We present maps of the 22 MHz radio emission between declinations -28 degr and +80 degr, covering ~ 73% of the sky, derived from observations with the 22 MHz radiotelescope at the Dominion Radio Astrophysical Observatory (DRAO). The resolution of the telescope (EW x NS) is 1.1 degr x 1.7 degr secant(zenith angle). The maps show the large scale features of the emission from the Galaxy including the thick non-thermal disk, the North Polar Spur (NPS) and absorption due to discrete H Ii regions and to an extended band of thermal electrons within 40 degr of the Galactic centre. We give the flux densities of nine extended supernova remnants shown on the maps. A comparison of the maps with the 408-MHz survey of \cite[Haslam et al. (1982]{haslam82}) shows a remarkable uniformity of spectral index (T~ nu (-beta ) ) of most of the Galactic emission, with beta in the range 2.40 to 2.55. Emission from the outer rim of the NPS shows a slightly greater spectral index than the distributed emission on either side of the feature. The mean local synchrotron emissivity at 22 MHz deduced from the emission toward nearby extended opaque H Ii regions is ~ 1.5 10(-40) Wm(-3) Hz(-1) sr(-1) , somewhat greater than previous estimates.