  The coexistence of coherently and incoherently oscillating parts in a system
of identical oscillators with symmetrical coupling, i.e., a chimera state, is
even observable with uniform global coupling. We address the question of the
prerequisites for these states to occur in globally coupled systems. By
analyzing two different types of chimera states found for nonlinear global
coupling, we show that a clustering mechanism to split the ensemble into two
groups is needed as a first step. In fact, the chimera states inherit
properties from the cluster states in which they originate. Remarkably, they
can exist in parameter space between cluster and chaotic states, as well as
between cluster and synchronized states.
