Astron. Astrophys. Suppl. Ser. 137, 7-19

The radio emission from the Galaxy at 22 MHz

R.S. Roger ¹ - C.H. Costain¹ - T.L. Landecker ¹ - C.M. Swerdlyk ^1,2

Send offprint request: R.S. Roger

1 - National Research Council Canada, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, Penticton, B.C. Canada V2A 6K3
e-mail: robert.roger@hia.nrc.ca
2 - Now at University of Victoria, Victoria, B.C., Canada

Received October 22, 1998; accepted January 4, 1999

Abstract:

We present maps of the 22 MHz radio emission between declinations -28$^\circ$  and +80$^\circ$, covering $\sim$73$\%$ of the sky, derived from observations with the 22 MHz radiotelescope at the Dominion Radio Astrophysical Observatory (DRAO). The resolution of the telescope (EW $\times$ NS) is 1.1$^\circ$ $\times$ 1.7$^\circ$ 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$^\circ$ 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 Haslam et al. (1982) shows a remarkable uniformity of spectral index ($T\propto \nu^{-\beta}$) 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 $\sim$1.5$\$10^-40 Wm^-3 Hz^-1 sr^-1, somewhat greater than previous estimates.

Key words: Galaxy: structure -- radio continuum: general; ISM