In the whirlpool's coils: tracing substructure from combined
  optical/X-ray data in the galaxy cluster A1300
  Structure formation is thought to act via hierarchical mergers and accretion
of smaller systems driven by gravity with dark matter dominating the
gravitational field. Combining X-ray and optical imaging and spectroscopy
provides a powerful approach to the study of the cluster dynamics and mass
assembly history. The REFLEX-DXL sample contains the most X-ray luminous galaxy
clusters (L_X > 10^45 erg/s) from the REFLEX survey at z = 0.27-0.31. We
present the photometric (WFI) and spectroscopic (VIMOS) data for the DXL
cluster RXCJ1131.9-1955 (Abell 1300); in combination with the existing X-ray
data we determine and characterise the substructure of this post-merging
system. We analyse X-ray selected groups in a 30' x 30' region encompassing the
cluster in order to study the mass assembly of A1300. The X-ray surface
brightness map of A1300 appears disturbed and exhibits the signature of a
forward shock, which is consistent with a previous analysis of radio data.
Moreover, we detect a large scale-filament in which the cluster is embedded and
several infalling groups. Comparison of the whirlpool-like features in the
entropy pseudo-map of the intra-cluster medium with the distribution of the
cluster members reveals a direct correspondence between the ICM structure and
the galaxy distribution. Moreover, comparison with existing simulations allows
us to better understand the dynamics of the cluster progenitors and to age date
their impact. A1300 is a complex massive system in which a major merging
occurred about 3 Gyr ago and additional minor merging events happen at
different times via filaments, that will lead to an increase of the cluster
mass of up to 60% in the next Gyr.
