Suzaku Observations of the Centaurus Cluster: Absence of Bulk Motions in the Intracluster Medium

The Centaurus cluster (z=0.0104) was observed with the X-ray ImagingSpectrometer (XIS) onboard the Suzaku X-ray satellite in three pointings, onecentered on the cluster core and the other two offset by +-8' in declination.To search for possible bulk motions of the intracluster medium, the centralenergy of He-like Fe-K line (at a rest-frame energy of 6.7 keV) was examined tolook for a positional dependence. Over spatial scales of 50 kpc to 140 kpcaround the cluster core, the central line energy was found to be constantwithin the calibration error of 15 eV. The 90% upper limit on the line-of-sightvelocity difference is |Delta_v|< 1400 km/s, giving a tighter constraint thanprevious measurements. The significant velocity gradients inferred from aprevious Chandra study were not detected between two pairs of rectangularregions near the cluster core. These results suggest that the bulk velocitydoes not largely exceed the thermal velocity of the gas in the central regionof the Centaurus cluster. The mean redshift of the intracluster medium wasdetermined to be 0.0097, in agreement with the optical redshift of the clusterwithin the calibration uncertainty. Implications of the present results for theestimation of the cluster mass are briefly discussed.