Merging young clusters in the Shapley supercluster

We present the ASCA spectral diagnostics of the X-ray-emitting gas of five clusters of galaxies in the Shapley concentration. X-rays from two rich clu sters, A3562 and A3558, nicely follow the standard L-X-k(B) T relation, whi le the X-ray luminosity of a poor cluster, A3556, comes below the relation line. The X-ray spectrum of another poor cluster, SC 1329-313, is found to be peculiar; the gas temperature is higher than that estimated from the vel ocity dispersion of its member galaxies. The energy of the iron K alpha lin e is also higher than that expected from the temperature of the plasma cons idered in ionization equilibrium and hence is attributable to a plasma in t he recombination-dominant phase. We infer that high-temperature gas and hig hly ionized iron are relies of past major merger events in the formation ph ase of poor clusters at several times 10(8) yr ago. The putative merger hea ted the gas to high temperature by the associated shock and produced highly ionized iron as well. The high-temperature gas is gradually cooled down by adiabatic expansion, but the temperature is presently still higher than th at expected from the velocity dispersion of galaxies. Iron atoms in the pla sma, on the other hand, remain in highly ionized states with irregularities in the temperature distribution. We propose a dynamical sequence of cluste rs in the Shaply concentration; SC 1329-313 is an ongoing merger, A3556 is a candidate for postmerger, SC 1327-312 is a relaxed poor cluster, while A3 562 and A3558 are already developed and rich clusters even with some merger s in succession. The Shapley concentration thus can be called a kindergarte n of clusters of galaxies.