Mass-velocity dispersion relation in HIFUGCS galaxy clusters

YONG TIAN^1*, PO-CHIEH YU², PENGFEI LI³, STACY S. MCGAUGH³, CHUNG-MING KO^1,4

¹Institute of Astronomy, National Central University, Taoyuan, Taiwan
²College of General Studies, Yuan-Ze University, Taoyuan, Taiwan
³Department of Astronomy, Case Western Reserve University, Cleveland, USA
⁴Department of Physics and Center for Complex Systems, National Central University, Taoyuan, Taiwan

* Presenter:YONG TIAN, email:yongtian@gm.astro.ncu.edu.tw

We investigate the mass-velocity dispersion relation (MVDR) in 29 galaxy clusters in the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS). We measure the spatially resolved, line-of-sight velocity dispersion profiles of member galaxies of these clusters, which we find to be mostly flat at large radii, reminiscent of the rotation curves of galaxies. We discover a tight empirical relation between the baryonic mass and the flat velocity dispersion of the member galaxies. The residuals of the relation, the MVDR of galaxy clusters, are uncorrelated with other cluster properties. These characteristics are reminiscent of the MVDR for individual galaxies, albeit about ten times larger characteristic acceleration scale. The cluster baryon fraction falls short of the cosmic value, exposing a problem: the discrepancy increases systematically for clusters of lower mass and lower baryonic acceleration.

Keywords: Dark matter, Galaxy clusters, Galaxy groups, Intracluster medium, X-ray astronomy