| As the largest bound systems, clusters of galaxies frequently locate at the knots of the filamentary structures in the universe. They are tracers of the large scale structure, and also the important laboratories for observing the interaction between galaxies and the environmental effect on the processes experienced during the evolution of galaxies.This thesis presents our multi-color optical photometry of the nearby galaxy clus-ter A2319(zc=0.0557) with the Beijing-Arizona-Taiwan-Connecticut (BATC) sys-tem, which is equipped with the60/90cm f/3Schmidt Telescope of National Astro-nomical Observatories of China (NAOC) at the Xinglong station. The BATC multi-color photometric system includes15intermediate band(a-k,m-p)filters, covering the whole optical wavelength range from about3000A to10000A. Within our viewing field of58’×58’centered on A2319,140galaxies with known spectroscopic red-shifts are extracted from the NASA/IPAC Extragalactic Database (NED), including137member galaxies (called sample Ⅰ). Both spatial distribution and localized velocity structure support the picture that A2319is a dynamically active cluster, in agreement with the X-ray images. The K-test confirms the existence of two substructures. The spatial distribution shows an irregular morphology, elongated in the NE-SW direc-tion. By applying virial theorem, we determine the masses of A2319A and A2319B, and find that A2319A is gravitationally bound to A2319B if the projection angle a is between22°and82°.For selecting faint member galaxies of A2319, the color-color diagram and photo-metric redshift technique are applied to the BATC spectral energy distributions (SEDs) of the objects detected. In order to exclude the fake candidates of faint member galax-ies which is induced from the severe contamination in BATC images with bad seeings by the foreground star field (due to low Galactic latitude (b～13°)), we take the u-band images with good seeing obtained with the90inch (2.3m) Bok telescope at Kitt Peak, which belongs to the Steward Observatory, University of Arizona. As a result,233faint member galaxies are finally selected. Combined with sample Ⅰ, an enlarged sample (called sample Ⅱ) of370member galaxies is achieved. On the basis of sam- ple Ⅱ, spatial distribution of member galaxies shows an irregular morphology with a dense main concentration. The bubble plot of A2319indicates a substructure at10’ along NW direction, which is consistent with previous research. A possible subcluster denoted with a bunch of bubbles is also found at18’ NW to the cluster center.Additionally, the stellar synthesis code, STARLIGHT, is applied to the SDSS spectra of242member galaxies in A85for studying the stellar populations and star formation histories of cluster galaxies. The star formation properties of galaxies, such as mean stellar age, metallicity, stellar mass and star formation rate, are investigated as the functions of local surface density. Our results indicate that the massive galaxies at the high-density region of cluster core show longer mean stellar ages, higher metal-licities, and lower specific star formation rates, and the recent star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and specific star formation rate with stellar mass are confirmed. As a group collabora-tion, this work has been completed for one year, and the paper has been accepted for publication in "Acta Astronomica Sinica". |
PDF Full Text Request