The Atlas of DRAGNs contains images of all the known DRAGNs which meet the following criteria (using the best information c. 1990):
To come: Map of the Northern sky showing positions.
The Galactic latitude limit excludes DRAGNs which are seen through the plane of our Galactic disk. Although radio waves pass unhindered through the disk, visible light is absorbed by interstellar dust, and hence, when there is a long line of sight through the disk, the host galaxies are difficult to even detect, let alone measure a redshift. We chose to make life easy for ourselves by avoiding the region of sky which is worst affected.
The declination limit was imposed because old-style aperture synthesis telescopes, arranged on an east-west line, produced very poor images of objects close to the equator. (To see why, try reading the MERLIN User's Guide).
The flux density limit selects the brightest couple of hundred DRAGNs in this region of sky. It corresponds to the limit at which the 3CR survey was reasonably complete; hence nearly all the sample members are in the 3CR list.
The redshift limit picks just the nearest 50% of the DRAGNs selected by the first three criteria. We did this because the more distant DRAGNs are being studied systematically by other groups.
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