| As the most massive gravitationally bound systems in the universe, galaxy clusters have long been recognized as entities that can provide vital clues to large-scale structure formation. They have aroused more and more interests since Abell (1958) achieved the catalogue of 2712 rich galaxy clusters. The star formation histories (SFHs) of member galaxies may shed some light on the evolution of their host clusters. Analysis of the cluster mass function, substructure features, and the star formation properties of cluster galaxies not only can provide convincing observational constraints on the cosmological models, but also contribute to our understanding of galaxy formation and evolution in dense environments.This thesis presents our investigations of cluster dynamics and the star for-mation properties of cluster galaxies on the basis of two galaxy clusters with completely different dynamical statuses, i.e., a merging cluster A2319 and a dy-namically relaxed cluster A1767. A summary of the main contents of our research is given below:Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. There are 142 galaxies with known spectroscopic redshifts within the BATC viewing field of 58’× 58’centered on this rich cluster, including 128 member galaxies (called sample I). A large ve-locity dispersion in the rest frame,1622-70+91 km s-1, suggests merger dynamics in A2319. The contour map of projected density and localized velocity struc-ture confirm the so-called A2319B substructure, at ～10’ northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V～20 mag. A u-band (～3551 A) image with better seeing and spatial resolution, obtained with the Bok 2.3m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photome-try. With color-color diagrams and photometric redshift technique,233 galaxies brighter than hBATC= 19.0 are newly selected as member candidates after an ex- clusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. Based on sample I and the enlarged sample of mem-ber galaxies (called sample II), subcluster A2319B is confirmed. The early-type galaxies are found to follow a tight color-magnitude correlation. The star for-mation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star for-mation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and higher interstellar medium metallicities. For the merging cluster A2319, local surface density is a better envi-ronmental indicator rather than the cluster-centric distance. Compared with the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is found in A2319, indicating that the galaxy-scale turbulence stimulated by the subcluster merger might have played a role in triggering the star formation activity.A1767 is a dynamically relaxed, cD cluster of galaxies. Among 250 spectro-scopically confirmed member galaxies within a projected radius of 2.5 r200,243 galaxies (～97%) are spectroscopically covered by the Sloan Digital Sky Survey (SDSS). Based on this homogeneous spectral sample, the stellar evolutionary synthesis code STARLIGHT is applied to investigate the stellar populations and star formation histories of galaxies in this cluster. The star formation proper-ties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates, are presented as functions of local galaxy density. A strong en-vironmental effect is found such that massive galaxies in the high-density core region of the cluster tend to have higher metallicities, older mean stellar ages, and lower specific star formation rates (SSFRs), and their recent (i.e., look-back time Υ< 24.5 Myr)star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and SSFR with stellar mass are confirmed. |
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