3 Galaxy distribution

Figure 1: Galaxies brighter than $b_{\rm J}^{\rm cosmos} = 19.75$ in the field of Abell 970. The plot is centered on galaxy number 1 in Table 1.

We present in Fig. 1 the distribution of galaxies in the direction of Abell 970, obtained from the COSMOS catalogue, for galaxies brighter than $b_{\rm J}^{\rm cosmos} < 19.75$ (235 objects). The plot is centered on an E/D galaxy (number 1 in Table 1) and has $45^\prime \times 45^\prime$ (i.e., about $4.6 \times 4.6$  h₅₀^-1 Mpc). It is interesting to point out that, amongst the galaxies with known velocities, this is the second brightest cluster galaxy ( $b_{\rm J}^{\rm cosmos} = 16.57$).

The adaptive kernel density map (Silverman 1986) corresponding to this sample is given in Fig. 2. This figure indicates that the galaxy distribution in the field of Abell 970 is approximately regular, with the projected density peaking at the position of the E/D galaxy. There is a substructure at NW, near galaxy number 40 in Table 1. This is the brightest cluster galaxy (considering only galaxies with known radial velocities); it is classified as S0/S and has magnitude $b_{\rm J}^{\rm cosmos} = 16.42$. This figure also indicates that the cluster radial extension may attain several Mpc.

It is worth noting that all features displayed in this map are significant. The significance regions are obtained through a bootstrap resampling procedure applied to the sample coordinate distribution. This allows the construction of a map of standard deviations of the projected density. By subtracting the projected density map from the standard deviation map (multiplied by a given number, say 3), we define the significance regions of the projected density map as those regions for which the resulting subtracted map is positive.