  To search for bulk motions of the intracluster medium, we analyzed the X-ray
spectra taken with the Suzaku satellite and measured the Doppler shift of Fe-K
line emission from eight nearby clusters of galaxies with various X-ray
morphologies. In the cores of the Centaurus and Perseus clusters, the gas bulk
velocity does not exceed the sound velocity, which confirms the results of
previous research. For the Cen45 subcluster, we found that the radial velocity
relative to the Centaurus core, <780 km s^-1, is significantly smaller than
that reported in the optical band at the 3.9 sigma level, which suggests an
offset between the gas and galaxy distributions along the line of sight due to
the subcluster merger. In A2199, A2142, A3667, and A133, no significant bulk
motion was detected, indicating an upper limit on the radial velocity of
3000-4000 km s^-1. A sign of large bulk velocity in excess of the instrumental
calibration uncertainty was found near the center of cool-core cluster A2029
and in the subcluster of the merging cluster A2255, suggesting that the
nonthermal pressure support is not negligible in estimating the total
gravitational mass of not only merging clusters but also relaxed clusters as
predicted by numerical simulations. To improve the significance of the
detection, however, a further examination by follow-up observations is
required. The present study provides a pilot survey prior to the future
high-resolution spectroscopy with ASTRO-H, which is expected to play a critical
role in revealing the dynamical evolutions of clusters.
