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5. Some important properties of the ENACS catalogue

  By themselves, the 107 clusters for which data is given in the present catalogue do not form a complete, volume-limited sample of tex2html_wrap_inline2025 1 Abell clusters. However, the ENACS was designed to establish, in combination with data available in the literature, a database for a complete, "local" sample of tex2html_wrap_inline2025 1 Abell clusters with redshifts < 0.1. In Sect. 2.2 of Paper II, the resulting complete sample of 128 tex2html_wrap_inline2025 1 clusters (with tex2html_wrap_inline2033 0.1, and in the solid angle defined by tex2html_wrap_inline2035 and tex2html_wrap_inline2037) has been described.

For 78 of these clusters, data were provided exclusively by the ENACS, while for 5 additional clusters the ENACS contributed to existing data. As discussed in Paper II, these 128 clusters represent a total of 158 tex2html_wrap_inline1861 10 clusters in a volume of 9.2 106 htex2html_wrap_inline2043. One of the results of the ENACS observations is that for 83 of the 128 clusters we have an improved estimate, through the redshifts, of the contribution to the cluster richness from background galaxies.

In the ENACS cluster sample there is a general bias against clusters with tex2html_wrap_inline2033 0.04, as those are too extended for efficient observation with the Optopus spectrograph. On the other hand, outside the "cone" described above, we could not (and did not) seek to reach completeness, and as a result clusters with tex2html_wrap_inline2047 0.05 are overrepresented in the ENACS, and for tex2html_wrap_inline2049 0.06 the ENACS is only complete within the "cone".

When selecting galaxy subsets from the ENACS catalogue it must always be remembered that, at the fainter magnitudes, galaxies without emission lines are significantly discriminated against in comparison with galaxies that have clear emission lines (see Sect. 2.5 of Paper III). As a result of the differences in the projected distributions of galaxies with and without emission lines, the application of a limit to the projected distance from the cluster centre influences the mix between early- and late-type galaxies (Sect. 5, ibid.).


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