The GRGs presented in Paper I have been selected from the WENSS survey using the criteria that they should have an angular size above and a distance from the galactic plane . We find in Paper I that a WENSS radio source is most likely included in the sample if Jy/arcmin, where is the integrated 325-MHz flux density, and the largest angular size of the radio source. We have called this the sensitivity limit of our selection. The total number of sources in the sample of Paper I is 47, but at low flux density levels (i.e. mJy) several candidate sources have not yet been identified, and some sources may have been missed because they have not been recognized as single structures. Therefore, we have selected a subsample of 26 sources on the basis of a flux density at 325 MHz, Jy. At such high flux densities, it is unlikely that a source has escaped detection or recognition as a GRG.
On basis of our sensitivity limit (see above), it is unlikely that a 1-Jy GRG will be recognized at a redshift below 0.014, due to its very low surface brightness in that case. However, the lowest redshift source in our sample is NGC315 at z=0.0167, so no source needed to be excluded on basis of this limit.
We have omitted two giant FRI-type (Fanaroff & Riley 1974) radio sources from the sample: 3C31 (e.g. Strom et al. 1983) and HB13 (e.g. Masson 1979). The considerations for doing so were the following. First, the observed size of sources of this class depends strongly on the surface brightness sensitivity of the radio observations; only for edge-brightened FRII-type sources, the angular size and source structure is reasonably well defined because of the presence of hotspots and the usually better outlined radio lobe morphology. The edge-darkened nature of FRI's makes it unlikely that the 1-Jy sample is complete for FRI-type sources. Second, the properties of the radio lobes of FRI-type sources are known to be different. This is shown, for instance, by the different spectral index distribution in the radio lobes (e.g. Jägers 1986; Parma et al. 1999), which may indicate different mechanisms for the acceleration and ageing of the radiating particles.
There are a few remaining sources which are strictly of type FRI, but also show properties commonly found in FRII-type sources, such as hotspots or sharply bound lobe structures. Well known examples of such sources are DA240, NGC315 and NGC6251. Since the measured size of these sources is better constrained, we have left these sources in the sample, although they are excluded from many of the analyses in this paper. They are indicated as type "FRI/II'' in Table 1.
Our 1-Jy sample therefore contains all non FRI-type sources with a 325-MHz flux density above 1 Jy, an angular size above , a linear size above 1 Mpc, a declination above , a distance from the galactic plane and a redshift above 0.014, in total 26 sources. Of these, 16 are GRGs which were previously known and 10 are newly discovered GRGs (see Paper I). The list of sources and some of their properties are presented in Table 1. The source B1918+516 has an uncertain redshift determination due to the faintness of its optical host galaxy and the difficulty we had in actually identifying it; an independent confirmation is needed.
|IAU name||Alt. name||z||Type||D|
|a-Redshift still uncertain (see text and Paper I).|
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