We present an analysis of stellar populations in passive galaxies in seven massive X-ray clusters at z = 0.19 - 0.89 .
Based on absorption line strengths measured from our high signal-to-noise spectra , the data support primarily passive evolution of the galaxies .
We use the scaling relations between velocity dispersions and the absorption line strengths to determine representative mean line strengths for the clusters .
From the age determinations based on the line strengths ( and stellar population models ) , we find a formation redshift of z _ { form } = 1.96 _ { -0.19 } ^ { +0.24 } .
Based on line strength measurements from high signal-to-noise composite spectra of our data , we establish the relations between velocity dispersion , ages , metallicities [ M/H ] and abundance ratios [ \alpha / Fe ] as a function of redshift .
The [ M/H ] –velocity dispersion and [ \alpha / Fe ] –velocity dispersion relations are steep and tight .
The age–velocity dispersion relation is flat , with zero point changes reflecting passive evolution .
The scatter in all three parameters are within 0.08–0.15 dex at fixed velocity dispersions , indicating a large degree of synchronization in the evolution of the galaxies .
We find indication of cluster-to-cluster differences in metallicities and abundance ratios .
However , variations in stellar populations with the cluster environment can only account for a very small fraction of the intrinsic scatter in the scaling relations .
Thus , within these very massive clusters the main driver of the properties of the stellar populations in passive galaxies appears to be the galaxy velocity dispersion .