  Central cool gas component that is often observed from a well-relaxed cluster
system has long been interpreted as a consequence of ``Cooling Flow'' (CF),
radiative cooling followed by inflow of Intra-Cluster Medium (ICM). However,
recent XMM-Newton spectroscopy has shown no signatures of cooler gas phases
below certain temperatures in typical CF clusters (A1795, Tamura et al. 2001;
A1835, Peterson et al. 2001). This contradicts the conventional CF model or at
least requires a major revision of the model. In order to investigate
statistical properties of the central cool component, we performed systematic
analysis of ASCA data on 85 clusters. We found that 1) temperature of the
central cool component strongly depends on the temperature of the main ICM, 2)
the cool component is selectively found around a brightest cluster galaxy (BCG)
that coincide with the X-ray peak position, and 3) the luminosity-temperature
(L-T) relation of the cool component shows nice agreement with the L-T relation
of the main ICM. Together with the previous observational fact that, in some of
the ``CF'' clusters, the total gravitating mass is clustering in two distinct
spatial scales, a main cluster component and a second small-scale system, we
conclude that the central cool component is associated with the second
small-scale self-gravitating system that is immersed in the host cluster, and
the cool component temperature reflects the gravitational potential depth.
