The Double Galaxy Cluster Abell 2465 I. Basic Properties: Optical
  Imaging and Spectroscopy
  Optical imaging and spectroscopic observations of the z = 0.245 double galaxy
cluster Abell 2465 are described. This object appears to be undergoing a major
merger. It is a double X-ray source and is detected in the radio at 1.4 GHz.
This paper investigates signatures of the interaction of the two components.
Redshifts were measured to determine velocity dispersions and virial radii of
each component. The technique of fuzzy clustering was used to assign membership
weights to the galaxies in each clump. Using redshifts of 93 cluster members
within 1.4 Mpc of the subcluster centres, the virial masses and anisotropy
parameters are derived. 37% of the spectroscopically observed galaxies show
emission lines and are predominantly star forming in the diagnostic diagram. No
strong AGN sources were found. The emission line galaxies tend to lie between
the two cluster centres with more near the SW clump. The luminosity functions
of the two subclusters differ. The NE component is similar to many rich
clusters, while the SW component has more faint galaxies. The NE clump's light
profile follows a single NFW profile with c = 10 while the SW is better fit
with an extended outer region and a compact inner core, consistent with
available X-ray data indicating that the SW clump has a cooling core. The
observed differences and properties of the two components of Abell 2465 are
interpreted to have been caused by a collision 2-4 Gyr ago, after which they
have moved apart and are now near their apocentres, although the start of a
merger remains a possibility. The number of emission line galaxies gives weight
to the idea that galaxy cluster collisions trigger star formation.
