Absence of Bulk Motions of the Intracluster Medium in the Centaurus Cluster

We present results from the Suzaku observations of a nearby cluster, the Centaurus cluster (z = 0.0104). Three pointing observations of the cluster were carried out with the Suzaku XIS in December 2005, and the Doppler shift of the iron K lines was investigated in detail to constrain the bulk velocity of the intracluster medium (ICM) in its core region. From the spectral analysis, no significant velocity difference was detected within calibration uncertainty of +/- 700 kms(-1) over a spatial scale of 50 kpc in the central 240 kpc region. The 90% upper limit on the line-of-sight velocity is < 1400 km s(-1), giving a tighter constraint than the previous measurements. The significant velocity gradients inferred from the previous Chandra observations were not detected in two pairs of regions near the cluster core. These results suggest that the bulk velocity does not largely exceed the thermal velocity of the gas in the central region of the Centaurus cluster. Implications of the present results for the estimation of the cluster mass are discussed.