Abstract. We present maps of the 22 MHz radio emission between declinations −28• and +80• , 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 × NS) is 1.1• × 1.7• 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• 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 ∝ ν −β ) of most of the Galactic emission, with β 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 −3Hz −1 sr −1 , somewhat greater than previous estimates.

Abstract.We describe an aperture synthesis radio telescope optimized for studies of the Galactic interstellar medium (ISM), providing the ability to image extended structures with high angular resolution over wide fields. The telescope produces images of atomic hydrogen emission using the 21-cm H i spectral line, and, simultaneously, continuum emission in two bands centred at 1420 MHz and 408 MHz, including linearly polarized emission at 1420 MHz, with synthesized beams of 1 and 3.4 at the respective frequencies. A full synthesis can achieve a continuum sensitivity (rms) of 0.28 mJy/beam at 1420 MHz and 3.8 mJy/beam at 408 MHz, and the 256-channel H i spectrometer has an rms sensitivity of 3.5B −0.5 sin δ K per channel, for total spectrometer bandwidth B MHz and declination δ. The tuning range of the telescope permits studies of Galactic and nearby extragalactic objects. The array uses 9 m antennas, which provide very wide fields of view of 3.1• and 9.6 • (at the 10% level), at the two frequencies, and also allow data to be gathered on short baselines, yielding extremely good sensitivity to extended structure. Single-antenna data are also routinely incorporated into images to ensure complete coverage of emission on all angular scales down to the resolution limit. In this paper we describe the telescope and its receiver and correlator systems in detail, together with calibration and observing strategies that make this instrument an efficient survey machine.

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