Cluster Sample
To investigate in a systematic way the correlations between cluster properties and cluster galaxy populations, a well-defined, large cluster sample is required, with available X-ray data and covering a wide range in optical and X-ray properties.
The selection of the cluster sample obeys three criteria:
1) X-Ray selection (from ROSAT-RASS):
Ebeling+1996 (XBAC): Fx > 5.0·10-12 erg cm-2 s-1
Ebeling+1998 (BCS): Fx > 4.4·10-12 erg cm-2 s-1
Ebeling+2000 (eBCS): Fx > 2.8·10-12 erg cm-2 s-1
2) Galactic latitude |b|>20°
3) Redshift range 0.04<z<0.07
The last criterion ensures both a large area coverage (34'=1.6 Mpc by side at z=0.04, worst case) and optimal spatial resolution for morphology and surface photometry studies (1"=1.3 kpc at z=0.07, worst case).
The selection criteria result in a sample of 77 clusters (36 in the Northern Hemisphere and 42 in the Southern)
The sample covers a broad range of richness, Bautz-Morgan class and X-ray luminosities, from clusters more X-ray luminous than Coma to clusters less luminous than Hercules.
More than a third of the clusters are in common with Dressler's (1980) sample. This will be useful for comparing the two dataset and the morphological classifications.