Discovery of a nearby early-phase major cluster merger CIZA J1358.9-4750
  CIZA J1358.9-4750 is a nearby (z = 0.074) pair of clusters of galaxies
located close to the Galactic plane. It consists of two X-Ray extended humps at
north-west and south-east separated by 14 arcmin (~ 1.2 Mpc), and an X-Ray
bright bridge-like structure in between. With Suzaku, the south-east hump was
shown to have a temperature of 5.6 keV and the north-west one 4.6 keV. Neither
humps exhibit significant central cool component. The bridge region has a
temperature higher than 9 keV at the maximum, and this hot region is
distributed almost orthogonal to the bridge axis in agreement with the shock
heating seen in numerical simulations at an early phase of a head-on major
merger. This resemblance is supported by good positional coincidence between
the X-Ray peaks and cD galaxies associated with each cluster. In a short
exposure XMM-Newton image, a significant intensity jump was found at a position
where the Suzaku-measured temperature exhibits a steep gradient. These
properties indicate the presence of a shock discontinuity. The Mach number is
estimated to be 1.32 from the temperature difference across the identified
shock front, which gives the colliding velocity of approximately 1800 km/s.
From optical redshifts of the member galaxies, the two clusters are indicated
to be merging nearly on the sky plane. Thus, CIZA J1358.9-4750 is considered as
a valuable nearby example of early-phase merger with a clear shock feature.
