The Las Campanas/Anglo-Australian Telescope Rich Cluster Survey - III. Spectroscopic studies of X-ray bright galaxy clusters at z~ 0.1

We present the analysis of the spectroscopic and photometric catalogues of 11 X-ray luminous clusters at 0.07 <z <0.16 from the Las CampanasAnglo-Australian Telescope Rich Cluster Survey. Our spectroscopic data set consists of over 1600 galaxy cluster members, of which two-thirds are outside r200. These spectra allow us to assign cluster membership using a detailed mass model and expand on our previous work on the cluster colour-magnitude relation (CMR) where membership was inferred statistically. We confirm that the modal colours of galaxies on the CMR become progressively bluer with increasing radius d(B-R)drp=-0.011 A? 0.003 and with decreasing local galaxy density d(B-R)dlog (I ) =-0.062 A? 0.009. Interpreted as an age effect, we hypothesize that these trends in galaxy colour should be reflected in mean HI equivalent width. We confirm that passive galaxies in the cluster increase in HI line strength as dHI drp= 0.35 A? 0.06. Therefore, those galaxies in the cluster outskirts may have younger luminosity-weighted stellar populations; up to 3 Gyr younger than those in the cluster centre assuming d(B-R)dt= 0.03 mag per Gyr. A variation of star formation rate, as measured by O iiI>3727 , with increasing local density of the environment is discernible and is shown to be in broad agreement with previous studies from the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey.