Pointing to the minimum scatter: the generalized scaling relations for galaxy clusters

We introduce a generalized scaling law, M tot = 10 K A a B b , to look for the minimum scatter in reconstructing the total mass of hydrodynamically simulated X‐ray galaxy clusters, given gas mass M gas , luminosity L and temperature T . We find a locus in the plane of the logarithmic slopes a and b of the scaling relations where the scatter in mass is minimized. This locus corresponds to b M =−3/2 a M + 3/2 and b L =−2 a L + 3/2 for A = M gas and L , respectively, and B = T . Along these axes, all the known scaling relations can be identified (at different levels of scatter), plus a new one defined as M tot ∝ ( LT ) 1/2 . Simple formula to evaluate the expected evolution with redshift in the self‐similar scenario is provided. In this scenario, no evolution of the scaling relations is predicted for the cases ( b M = 0, a M = 1) and ( b L = 7/2, a L =−1), respectively. Once the single quantities are normalized to the average values of the sample under considerations, the normalizations K corresponding to the region with minimum scatter are very close to zero. The combination of these relations allows one to reduce the number of free parameters of the fitting function that relates X‐ray observables to the total mass and includes the self‐similar redshift evolution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90057/1/j.1365-2966.2011.20318.x.pd