Submitted to the Astrophysical Journal Sup. Series Constraints on Intracluster Gas Bulk Motions in Clusters of Galaxies with ASCA

The recent detection of Doppler shifts of X-ray spectral lines in the intraclus-ter gas of the Centaurus and Perseus clusters of galaxies with ASCA has raised the question of the frequency of such velocity gradients and their relation to other cluster properties. To address this and improve the sample of ICM velocity gradi-ent candidates we carried out a systematic search of the ASCA archive for clusters with suitable observing conditions that allow full azimuthal mapping of gas ve-locities near the central regions. Here we present the results of the azimuthal velocity distribution of a sample consisting of the \best " observed clusters for velocity analysis. Our sample encompasses clusters with dierent physical and morphological characteristics, including both well behaved \cooling flow " and dynamically active clusters. The gas temperatures of the clusters in our sample range from 1.4 keV to 6.3 keV. We nd velocity substructures in 15 % of the clusters in our sample on the order of a few 103 km s−1. The signicance of the velocity gradients ’ is greater than 99 % in Abell 576 and RXJ0419.6+0225, the clusters where velocity gradients are most signicant. The velocity gradients are consistent with transitory and/or rotational bulk motion. The velocity gradients in these clusters are unlikely to be due to projected temperature anisotropies, AS-CA PSF, intrachip gain variations, and flux contamination from other sources. Chandra images of these clusters do not show obvious cluster alignments within the eld of view covered by ASCA. We also noticed a high frequency (50%) of anisotropic temperature gradients in the core of \cooling flow " clusters, suggest-ing the presence of frequent dynamical activity in the core of galaxy clusters