4 Results

The velocity measurements obtained in this work are listed in Table 2 as follow:
Column 1: the CGCG designation (Zwicky et al. 1961-68).
Columns 2, 3: (B1950) celestial coordinates, measured with few arcsec uncertainty.
Column 4: the photographic magnitude (Zwicky et al. 1961-68).
Columns 5, 6: the derived heliocentric velocity with uncertainty. The latter quantity is obtained by adding in quadrature systematic and statistical errors.
Column 7: an asterisk marks uncertain redshifts. These are either low signal spectra or spectra with only one absorption line that could be misidentified.
Column 8: type of lines (A = absorption; E = emission; EA = both).
Column 9: method used for the redshift measurement (CC = cross correlation; IL = individual line measurement).
Column 10: observing run.

  

Table 2: Parameters of the observed galaxies

  

Table 2: continued

  

Table 2: continued

  

Figure 1: The distribution in celestial coordinates of 1085 galaxies in the direction of the Coma-A 1367 supercluster, panel a). A wedge diagram ($V_{\rm CMB}$ vs. R.A.) is given in panel b). Small symbols mark galaxies taken from the literature, filled circles mark the measurements obtained in this work

Figure 1 gives a representation in celestial coordinates of 1085 galaxies (panel a) and a wedge diagram ($V_{\rm CMB}$ vs. R.A.) is given in panel b. Small symbols mark galaxies taken from the literature, filled circles mark the measurements obtained in this work.

  

Figure 2: Velocity histogram of the 1085 available redshifts, panel a), of the 102 redshifts obtained in this work, panel b) and of the ratio of new to all redshifts, panel c)

Figure 2 gives a histogram of the galaxy velocity distribution (panel a). The present measurements are given in a separate histogram (panel b). Since, for obvious reasons, we measured galaxies fainter than average, the fraction of background objects (panel c) is higher than in the general sample. However, even at the present limiting magnitude, nearly 50% of the new redshifts are found in the range 6000-8500 $\rm km\,s^{-1}\!$, typical of the Coma supercluster.

4.1 The 3-D structure of the Coma-A 1367 supercluster

The aim of this work is to try an objective determination of the "aggregation" state of galaxies in the Coma-A 1367 supercluster, i.e. to establish the membership of galaxies to structures of a given size and complexity (e.g. clusters, groups, multiplets etc.) or their degree of "isolation". This is not a trivial exercise since this definition depends on two arbitrary quantities: the scale on which the local density is computed and the local density itself. Consider for example a pair of galaxies with a separation of say 100 kpc. This doublet could be relatively isolated in space, or embedded in a group of galaxies, or in a much larger cluster containing hundreds of galaxies. These three cases, in spite of their similar local densities (i.e. computed on 100 kpc radius), are subject to extremely different environmental conditions: the first (isolated pair) is dominated by the gravitational (tidal) force induced by its companion, whereas in the second example the prevailing conditions are dictated by the group potential and in the third by the large-scale cluster potential or might be severely influenced by the diffuse intracluster gas (e.g. ram pressure). These prevailing environmental conditions are thus "described" by a density parameter which must be computed within a radius similar to the typical scale of the aggregate. Once the densities are computed, these can be converted into (mutually exclusive) "aggregation" classes using appropriate density thresholds.

4.2 The 3-D algorithm

The structure of the Coma-A 1367 supercluster stands out clearly in Figs. 1 and 2 as the pronounced density enhancement centered at 7200 $\rm km\,s^{-1}\!$, stretching through the entire R.A. window. Conspicuous features are: the "fingers of god" of the two clusters Coma and A 1367 which span the interval 4000<V<10000 $\rm km\,s^{-1}$ and the large "void" in front of the supercluster. The remaining objects, belonging to the bridge between the two clusters have a narrower velocity distribution, which lies within the interval of roughly 6000<V<8500 $\rm km\,s^{-1}\!$.

To reconstruct the 3-D structure of the supercluster we proceed as follows:

1) Clusters (Agg = 1 to 4): we identify the members of the two rich clusters using a preliminary conservative positional criterion: in the velocity range 4000<V<10000 $\rm km\,s^{-1}$ there are 72 galaxies within 1 deg radius (Agg = 1) and 177 within 2 deg (Agg = 2) of the Coma cluster and 59 galaxies within 0.5 (Agg = 3.0) and 81 within 1 deg radius of A 1367 (Agg = 4.0). We subtract these objects from the sample.

2) "Homunculus" (Agg = 16): we identify on a purely positional basis the members of the "legs of the homunculus" (see de Lapparent et al. 1986) (Agg = 16) and we subtract these objects from the sample.

3) Foreground (Agg = 8 to 18): we subtract from the remaining sample all galaxies with V<6000 $\rm km\,s^{-1}\!$, which are considered as foreground objects. These are empirically assigned to individual groups and structures on the basis of their 3-D coordinates (Agg = 8 to 18 as defined in Gavazzi 1987) (see Table 3 below for details). Figure 3 gives a representation in celestial coordinates of the foreground galaxies (including Agg = 16) panel a) and a wedge diagram ($V_{\rm CMB}$ vs. R.A.) is given in panel b.

  

Figure 3: The distribution in celestial coordinates of galaxies in the foreground (Agg = 8-18) of the Coma-A 1367 supercluster, panel a). A wedge diagram is given in panel b)

4) Background (Agg = 19.0): we subtract from the remaining sample all galaxies with V>8600 $\rm km\,s^{-1}\!$, which are considered as background objects.

5) Groups (Agg = 5.): on the remaining sample (6000<V<8600 $\rm km\,s^{-1}$) we run an algorithm that counts around each galaxy the number of galaxies found within 0.9 Mpc projected radius, satisfying the additional requirement that their velocity is within 600 $\rm km\,s^{-1}$ from the mean velocity of the aggregate under study (850 $\rm km\,s^{-1}$ for group 5.3). If there are at least 8 such galaxies, these are assigned to the "group" class (Agg = 5). 5 groups are found by the algorithm (N3937, N4065, IC 762, N4213 and IC 3165) (see Table 3 for details). Figure 4 gives a representation in celestial coordinates of the groups members (panel a) and a wedge diagram is given in panel b. Different symbols are used for the various groups.

  

Figure 4: The distribution in celestial coordinates of galaxies belonging to 5 groups (Agg = 5) in the Coma-A 1367 supercluster, panel a). A wedge diagram is given in panel b)

6) Multiplets (Agg = 6.2 to 6.5): on the remaining sample (6000<V<8600 $\rm km\,s^{-1}$) we run an algorithm that counts around each galaxy the number of galaxies found within 0.3 Mpc projected radius satisfying the additional requirement that their velocity is within 600 $\rm km\,s^{-1}$ from the mean velocity of the aggregate under study. If there is at least 1 such galaxy, these are assigned to the "multiplet" class (Agg = 6). (6.2 = doublets, 6.3 = triplets... 6.5 = quintuplets).

7) Contact multiplets (Agg = 6.1): we repeat 6) with a more stringent requirement that the companion galaxy lies within 50 kpc. these are contact doublets and triplets. Figure 5 gives a representation in celestial coordinates of the members to multiplets (panel a) and a wedge diagram is given in panel b.

  

Figure 5: The distribution in celestial coordinates of galaxies belonging to multiplets (Agg = 6) in the Coma-A 1367 supercluster, panel a). A wedge diagram is given in panel b)

8) Isolated (Agg = 7.0): on the restricted velocity range 6000<V<8000 $\rm km\,s^{-1}$ we count galaxies which do not have a companion within 0.3 Mpc projected radius. We call these isolated (Agg = 7.0).

9) Strictly isolated (Agg = 7.1) we repeat 8) with the more stringent requirement that the galaxy under study is isolated within 0.5 Mpc projected radius. Figure 6 gives a representation in celestial coordinates of the isolated objects (panel a) and a wedge diagram is given in panel b.

  

Figure 6: The distribution in celestial coordinates of isolated galaxies (Agg = 7) in the Coma-A 1367 supercluster, panel a). A wedge diagram is given in panel b)

10) Extended clusters: finally we re-inject in the sample the cluster objects (see step 1) and try an alternative, less restrictive definition of cluster membership, which includes more peripheral objects. We count around each galaxy, in the interval 4000<V<10000 $\rm km\,s^{-1}\!$, the number of galaxies found within 2.0 Mpc projected radius. Within 2<R<8.5 deg of the center of Coma and 1<R<3.5 deg of the center of A 367 we allow for a velocity difference of 1500 $\rm km\,s^{-1}$ from the mean velocity of the cluster. In both aggregates we consider a galaxy to belong to the "extended cluster" if there are >20 galaxies satisfying the above criterion. Figure 7 gives a representation in celestial coordinates of the cluster members (panel a) and a wedge diagram is given in panel b. Different symbols are used for the core, outskirt and extended cluster members.

  

Figure 7: The distribution in celestial coordinates of galaxies belonging to the Coma and A 1367 clusters (Agg = 1-4), panel a). A wedge diagram is given in panel b)

  

Figure 8: The distribution in celestial coordinates of members (Agg = 1-7) to the Coma-A 1367 supercluster, panel a). A wedge diagram is given in panel b)

Figure 8 gives a representation in celestial coordinates of the supercluster members (panel a) and a wedge diagram is given in panel b.

All the above aggregation classes (1-19) are mutually exclusive, except the definition of extended cluster. A galaxy belonging to the extended cluster can be previously defined as belonging to a group, multiplet or even be considered isolated.

  

Table 3: The criteria used to define each "Aggregate" in the direction of the Coma-A 1367 supercluster

The criteria used above are summarized in Table 3 as follows: For any Agg class (Col. 1) a decription is given in Col. 2.
Column 3: the minimum number of objects used to compute the threshold density of each aggregate.
Column 4: the scale (R in Mpc; $\theta$ in degrees) used to compute the threshold density of each aggregate.
Columns 5, 6: the "window" in celestial coordinates where each aggregate was found. A single coordinate gives the center of the aggregate (with radius R or $\theta$). If a pair of coordinates is given this indicates the interval where the aggregate was found.
Column 7: the allowed velocity difference from the average velocity of the aggregate.
Columns 8, 9: the velocity interval where the aggregate was found.
Column 10: the average velocity of the aggregate.
Column 11: the number of objects belonging to each aggregate.