TheLX‐TandLX‐σ Relationships for Galaxy Clusters Revisited

The relationships between the X-ray determined bolometric luminosity Lx, the temperature T of the intracluster gas, and the optical measured velocity dispersion σ of the cluster galaxies are updated for galaxy clusters using the largest sample of 256 clusters drawn from literature. The newly established relationships, based on the doubly weighted orthogonal distance regression (ODR) method, are justified by both their self-consistency and co-consistency, which can then be used to test the theoretical models of cluster formation and evolution. The observationally determined Lx-T and Lx-σ relationships, Lx ∝ T 2.72±0.05 ∝ σ 5.24±0.29, are marginally consistent with those predicted in the scenario that both intracluster gas and galaxies are in isothermal and hydrostatic equilibrium with the underlying gravitational potential of clusters. A comparison between these observed and predicted Lx-T relationships also suggests that the mean cluster baryon fraction fb remains approximately constant among different clusters, fb ≈ 0.17, which gives rise to a low-mass density universe of Ωm ≈ 0.3.