Characterising galaxy groups: spectroscopic observations of the
  Shakhbazyan sample
  Groups of galaxies are the most common cosmic structures. However, due to the
poor statistics, projection effects and the lack of accurate distances, our
understanding of their dynamical and evolutionary status is still limited. This
is particularly true for the so called Shakhbazyan groups (SHK) which are still
largely unexplored due to the lack of systematic spectroscopic studies of both
their member galaxies and the surrounding environment. In our previous paper,
we investigated the statistical properties of a large sample of SHK groups
using Sloan Digital Sky Survey data and photometric redshifts. Here we present
the follow-up of 5 SHK groups (SHK 10, 71, 75, 80, 259) observed within our
spectroscopic campaign with the Telescopio Nazionale Galileo, aimed at
confirming their physical reality and strengthening our photometric results.
For each of the selected groups we were able to identify between 6 and 13
spectroscopic members, thus confirming the robustness of the photometric
redshift approach in identifying real galaxy over-densities. Consistently with
the finding of our previous paper, the structures studied here have properties
spanning from those of compact and isolated groups to those of loose groups.
For what the global physical properties are concerned (total mass,
mass-to-light ratios, etc.), we find systematic differences with those reported
in the literature by previous studies. Our analysis suggests that previous
results should be revisited; we show in fact that, if the literature data are
re-analysed in a consistent and homogeneous way, the properties obtained are in
agreement with those estimated for our sample.
