Studying The Distribution Of Galaxies By Cluster Analysis

The Sloan Digital Sky Survey (SDSS) is one of the largest astronomical surveys to date. The SDSS contains two galaxy samples:the Main galaxy sample and the Luminous Red Galaxy (LRG) sample, which are located in different redshift ranges and have different optical properties. The whole research work of this paper is based on these two galaxy samples.I focused on the two problems:super-large-scale structures of universe and the dependence of clustering properties of galaxies on physical parameters. I used cluster analysis. By this method, the galaxy sample can be separated into isolated galaxies, close double galaxies, galaxy groups or clusters and even superclusters. This actually probe the structures at different scales. The main conclusions can be summarized as follows:1. The super-large-scale structures in the Sloan Digital Sky Survey(1)The Sloan Great Wall is located at a median redshift of z=0.07804, the total length is about433Mpc, and the mean galaxy density is about six times that of the whole sample. In the Sloan Great Wall, sizes of86.1%galaxies range from2to6kpc, faint (fainter than Mr=-19.5) and brighter (brighter than Mr=-22) galaxies are very rare.(2) The CFA Great Wall is located at a median redshift of z=0.03058, and the total length is about251Mpc. sizes of about71.4%galaxies range from1to3kpc. The proportion of galaxies fainter than Mr=-19is about51.2%. The proportion of galaxies fainter than Mr=-19.5is as high as73.5%.(3) There are relatively few early-type galaxies in the CFA Great Wall.2. The further study of the Sloan Great Wall:I selected50942Main galaxies having the same redshift region (0.07≤z≤0.09) as the Sloan Great Wall from the Main galaxy sample, and construct our SubMain sample. From SubMain sample,2013isolated galaxies are identified. The comparative studies of galaxy properties among the Sloan Great Wall, isolated galaxies and the SubMain sample in different redshift bins are performed. (1) The statistical properties of luminosities and sizes of galaxies for the Sloan Great Wall, isolated galaxies and the SubMain sample are almost the same. These properties of galaxies may have no correlation with the environment or clustering.(2) In the Sloan Great Wall, the proportion of early-type galaxies is about22.17%, and approximates to that (21.83%) of the SubMain sample, while the proportion of early-type isolated galaxies is only14.46%. In different redshift bins, the early-type proportion of member galaxies of the Sloan Great Wall is apparently higher than that of isolated galaxies. This indicates that the morphological type of galaxies is closely correlated with the environment.(3) The g-r color of member galaxies of the Sloan Great Wall is redder than that of isolated galaxies on the average. This further confirms that clustering properties of galaxies depend on color.3. The clustering properties of Luminous Red Galaxies:I study the clustering properties of Luminous Red Galaxies (LRGs) and compare them with those of Main galaxies.(1) Clustering systems of LRGs mainly are close double and multiple galaxies, galaxy groups or poor clusters. The structure of the Main galaxy sample is more filamentary, while that of the LRG sample is a simple and central clustering.(2) The clustering properties of Luminous Red Galaxies apparently is different from those of Main galaxies.(3) The luminosity distribution of LRGs does not depend on the environments around galaxies.4. Clustering properties of galaxies with different galaxy morphologiesIt is found that the distribution of the late-type galaxies is more filamentary, that for late-type galaxies, the fractions of single, close double and multiple galaxies are higher, but the fraction of grouped galaxies is lower than the one of early-type galaxies.5. Dependence of clustering on galaxy color for Main galaxy sample(1) In galaxy samples with different color, super-large-scale structures are not observed, and richer and larger systems can be more easily formed in the redder samples. In addition, in the samples with redder color, the average size of the systems as a function of the dimensionless radius r preferentially become larger.(2) All analyses of the multiplicity functions can reach the same conclusion:the redder galaxies preferentially inhabit the dense groups and clusters.(3) Only according to the percolation radius, one very difficultly reach any conclusions about the color dependence of the filaments.6. Color dependence of clustering properties of Luminous Red Galaxies (LRGs):I preferentially conclude that the clustering properties of LRGs are not strongly correlated with colors.