The first sample is composed of 21 almost isolated early-type galaxies
characterized by the presence of shells, selected from
the Malin & Carter (1983) catalogue (Table 1).
The second one consists of 30 members of
isolated binary systems taken from the Reduzzi & Rampazzo (1995: RR95)
catalogue (Table 2) and characterized by various kinds of fine structures. Note
that we detect a double nucleus in the galaxy E2400100 (Table 1), unlike
other authors that have previously studied this object
(Malin & Carter 1983; Carter et al. 1988).
In the following we refer to E2400100 as two separate
galaxies, indicated as E2400100 A and B.
![]() |
Figure 1: Distribution of magnitudes (top panel) and of morphological types (bottom panel) within the two subsamples |
Figure 1 shows the distributions of the
morphological type and total apparent blue magnitude.
A few galaxies in the pair sample are of type later than T=0: their
spectra are presented for completeness, both in the present and in the
kinematical study (Paper II). Both pairs and shell galaxies
are located in low density environments, as mentioned above. In the
ESO-LV catalogue (Lauberts & Valentijn 1989),
the parameter characterizes the surface density of galaxies within one degree from a
specific object. Lauberts & Valentijn (1989)
consider that
describes rich environments, e.g. Fornax cluster.
With the exclusion of a few objects (namely NGC 1316 in Fornax, NGC 3289, RR 405a
and RR 405b) the average
value for the pair members is
2
1.5, while for shell galaxies is 1.5
0.9, indicating that
they are in very low density environments.
We consider 5 additional galaxies (Table 3), selected from the G93
sample. We use them as spectrophotometric "templates'' to
check the transformation of our indices into the
Lick-IDS "standard'' system (see Sect. 4).
We wish to emphasize that the selected sample complements that of G93. The latter author considers "normal'' early-type galaxies, i.e. without fine structures, most of which are in dense environments like the Virgo cluster centre or in groups (Cetus Aries, Libra cloud etc.) (see Tully 1988).
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