0.165?We will now discuss in some detail the nature and environment of the cluster Cl 0053-37. As we have already mentioned, Cl 0053-37 is visible in the field of the poor Abell cluster S0102. The first question, of course, is whether the former is a substructure of the latter.
For Cl 0053-37 we measured a redshift of 
, which is inconsistent
with the estimated distance of S0102. Consequently there are two
possibilities: either Cl 0053-37 is a true concentration
in S0102 - in which case the distance class of S0102 would have been
underestimated - or it is a background cluster seen through
S0102. From visual inspection of the ESO field F295 which
contains the cluster, the latter hypothesis seems more plausible.
The redshift of a galaxy near the center of S0102 was measured by
Bica et al. (1991), and is 
. More recently,
S0102 was selected with an automatic algorithm in the EDCC survey
(Collins et al. 1995) where it was identified as EDCC494: its redshift
(on the basis of 3 galaxies) is 
.
Therefore, it is clear that Cl 0053-37 is a new cluster, independent
of S0102, seen in projection.
However, it is unlikely that this background cluster
could contaminate the estimate of the
S0102 richness class, because the galaxies in Cl 0053-37 are significantly
fainter than the members of S0102.
Now, it is interesting to note that there are two southern surveys
not far from our cluster: the Las Campanas Redshift Survey
(LCRS; Shectman et al. 1996) and the Eso Slice Project
(ESP; Vettolani et al. 1997).
In particular, the slice of the LCRS centered at 
(1.5 degrees wide) was checked to obtain other redshifts for Cl 0053-37
and to search for structures related to this cluster.
We used NED (which now includes LCRS) to look for
all objects within 2 degrees from the cluster center.
Nearly all of them belong to the first strip of the LCRS,
and their redshift histogram is shown in Fig. 5 (click here).
There are three main peaks: the first, at , corresponds
to the redshift of S0102, the second one, at 
,
probably corresponds to a large structure identified in the ESP
some degrees below, the third, impressive peak (taking into account
the decreasing selection function) is at 
,
and corresponds to the redshift of Cl 0053-37.
Are these objects members of Cl 0053-37?
Figure 6 (click here) shows the projected distribution of all galaxies in a redshift range
, corresponding to the peak in the histogram of
Fig. 5 (click here). It is quite clear that we have
a linear structure with a void quite well defined on the left,
which crosses the whole 1.5 degrees of the LCRS strip, includes
our cluster, and possibly also a QSO found at the same redshift
(Hewitt & Burbidge 1989).
If this QSO belongs to the same structure or
not, is not possible to assess in the absence of other data.
Figure 5: Redshift
histogram of the LCRS galaxies within 2 degrees of Cl 0053-37 center
Figure 6: Map of all LCRS galaxies with a redshift between 0.160 and
0.170, with Cl 0053-37 and a QSO
At z = 0.165, 1 
Mpc corresponds to about
9 arcmin (q0 = 0.5):
the objects in the LCRS reach distances more than 10 Mpc from the cluster
center. This corresponds to a supercluster scale.
All these elements suggest that Cl 0053-37 belongs to a larger,
coherent structure with a possible size of 30 Mpc in the 
direction
and along the line of sight. In the 
direction it appears
less extended, no more than a few Mpc Mpc, and it
might be a wall between voids.
The elongation of the cluster, originally remarked by
Abell et al. (1989),
does not follow the elongation of the large-scale structure
defined by the LCRS galaxies, the quasar, and the cluster itself.
Perhaps the cluster is at some intersection of structures;
however, the exact topology of the region and a more detailed dynamical study
will require further data.