DRAO 22 MHz Map
HEALPix, nested, res 8 (Nside=256)
1.2° x 1.7° secant(zenith angle)
Original Data Source
Roger et al. (1999) presented a map of the 22 MHz radio emission between declinations -28° and +80°, covering ~73% of the sky, derived from observations with the 22 MHz radiotelescope of the Dominion Radio Astrophysical Observatory (DRAO). The resolution of the telescope (EW x NS) is 1.2° x 1.7° secant(zenith angle). Roger et al. emphasize that the main value of the data lies in the representation of structure larger than the beam. The strongest point sources (Cas A, Cyg A, Tau A and Vir A) have been removed from the map.
The Centre d'Analyse de Données Etendues group used the data to form an all-sky HEALPix format map following the method described in Appendix A of Paradis et al. 2012, A&A, 543, 103, ADS. Their HEALPix map is provided here. LAMBDA made a new version of the FITS file with minor changes to the headers to make them compliant with FITS standards. The map is in units of K brightness temperature. Map pixels are set to a sentinel value of -32768.0 for unobserved regions and for regions affected by sidelobes around Cyg A, Tau A, and Vir A.
The original WCS format data is available from the Max Planck Institute for Radioastronomy Survey Sampler site.
More details can be found in:
Roger et al. (1999), A&AS, 137, 7, ADS