Stellar populations of X-Ray luminous clusters at z = 0.1

Abstract

This thesis presents new and unique wide-field imaging and spectroscopic observations of 21 X-ray selected rich clusters of galaxies in the redshift range 0.07 < z < 0.16 from the Las Campanas Observatory (LCO) / Anglo-Australian Telescope (AAT) Rich Cluster Survey (LARCS). Mosaic two colour broad-band CCD imaging extending to 10 Mpc at the mean redshift of the survey have been taken at LCO; comprising over 50Gb of raw data. A reduction pipeline is developed for these data and catalogues are constructed for these clusters. Four of these fields are compared to the APM catalogue (Maddox et al. 1990) to confirm their photometric accuracy. In making the comparison several populations of galaxies are discovered to be absent from the APM.A statistical background correction technique is developed to examine the photometric properties of cluster members. Eleven clusters are combined together to investigate environmental trends in the stellar populations of the combined sample. It is found that the modal colours of galaxies lying on the colour-magnitude relation in the clusters become bluer by d (B - R)/dr(_p) = -0.022 ±0.004 with radius or d (B - R)/dlog(_10) (Σ) = -0.076 ± 0.009 with local galaxy density. The 2dF spectroscope at the A AT is used to make spectroscopic follow-up observations of three clusters. A reduction pipeline for these data is developed and redshifts for the galaxies are determined. The spectral catalogues are used to define cluster membership and confirm the photometric environmental trends. Spectral line strengths are used to classify the galaxy population and examine environmental trends across the clusters. The cluster cores are found to be predominantly passive compared to the field. A comparison of the two cluster membership assignment techniques underscores the need for spectroscopy to define the cluster population.