[en] From each of two volume-limited main galaxy samples of the Sloan Digital Sky Survey data release 7, a paired galaxy sample and an isolated galaxy sample are constructed and comparative studies between the star formation of galaxies in pairs and isolated are performed to explore influences of galaxy interactions on star formation. It is found that isolated galaxies have an enhancement of the star formation rate and the specific star formation rate, which suggests that interactions between galaxies are not the trigger of enhanced star formation. (author)

[en] I investigate the environmental dependence of galaxy colors in the CMASS sample of the Sloan Digital Sky Survey Data Release 9 (SDSS DR9). To decrease the radial selection effect, I divide the CMASS sample into subsamples with a redshift binning size of Δz = 0.01 and analyze the environmental dependence of the u − r, u − g, g − r, r − i and i − z colors for these subsamples in each redshift bin. Statistical analysis shows that all five colors weakly correlate with the local environment, which may mean that the environmental processes responsible for a galaxy's properties proceed slowly over cosmic time

[en] Using the LOWZ and CMASS samples of the ninth data release (DR9) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), I investigate properties of star forming galaxies and active galactic nuclei (AGNs). The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 ≤ z ≤ 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same

[en] Using galaxy data from the Sloan Digital Sky Survey Data Release 8, I explore whether the concentration index is a good morphological classification tool and find that a reasonable sample of pure late-type galaxies can be constructed with the choice of the r-band concentration index ci=2.85. The opposite is not true, however, due to the fairly high contamination of an early-type sample by late-type galaxies. In such an analysis, the influence of selection effects is less important. To disentangle correlations of the morphology and concentration index with stellar mass, star formation rate (SFR), specific star formation rate (SSFR) and active galactic nucleus (AGN) activity, I investigate correlations of the concentration index with these properties at a fixed morphology and correlations of the morphology with these properties at a fixed concentration index. It is found that at a fixed morphology, high-concentration galaxies are preferentially more massive and have a lower SFR and SSFR than low-concentration galaxies, whereas at a fixed concentration index, elliptical galaxies are preferentially more massive and have a lower SFR and SSFR than spiral galaxies. This result shows that the stellar mass, SFR and SSFR of a galaxy are correlated with its concentration index as well as its morphology. In addition, I note that AGNs are preferentially found in more concentrated galaxies only in the sample of spiral galaxies.

[en] Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we investigate the dependence of the clustering properties of galaxies on stellar velocity dispersion by cluster analysis. It is found that in the luminous volume-limited Main galaxy sample, except at r=1.2, richer and larger systems can be more easily formed in the large stellar velocity dispersion subsample, while in the faint volume-limited Main galaxy sample, at r≥0.9, an opposite trend is observed. According to statistical analyses of the multiplicity functions, we conclude in two volume-limited Main galaxy samples: small stellar velocity dispersion galaxies preferentially form isolated galaxies, close pairs and small group, while large stellar velocity dispersion galaxies preferentially inhabit the dense groups and clusters. However, we note the difference between two volume-limited Main galaxy samples: in the faint volume-limited Main galaxy sample, at r≥0.9, the small stellar velocity dispersion subsample has a higher proportion of galaxies in superclusters (n≥200) than the large stellar velocity dispersion subsample.

[en] Using the LOWZ (0.15 ≤ z ≤ 0.43) and CMASS (0.43 ≤ z ≤ 0.7) galaxy samples of the ninth data release from the Sloan Digital Sky Survey (SDSS) III Baryon Oscillation Spectroscopic Survey (BOSS),we investigate the environmental dependence of stellar mass of BOSS galaxies, and conclude that like the luminous red galaxy sample of the SDSS, the environmental dependence of stellar mass of BOSS galaxies is fairly weak. Results of this work also show that the CMASS sample with the redshift 0.43 ≤ z ≤ 0.7 used by many authors seriously suffers from the radial selection effect. (author)

[en] Using the MAIN galaxy data from the SDSS Data Release 4 (SDSS4), we further study the Sloan Great Wall by three-dimensional cluster analysis. Because the basic properties of Main galaxies change with redshift, we select 50942 Main 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 the SubMain sample, 2013 isolated galaxies are identified at dimensionless radius r = 1.4. We perform the comparative studies of galaxy properties among the Sloan Great Wall, isolated galaxies and the SubMain sample in different redshift bins. It turns out that the statistical properties of luminosities and sizes of galaxies for the Sloan Great Wall, isolated galaxies and the SubMain sample are almost the same, the proportion of early-type isolated galaxies is relatively low. We also d that mean color of member galaxies of the Sloan Great Wall is redder than that of isolated galaxies. These results indicate that some properties of galaxies may be closely correlated with the environment or clustering. (author)