Cheng-Hong Luo

The main galaxy groups from the SDSS data release 5

Aims. We investigate the correlations between galaxy properties and environment. Methods. From the main galaxy sample of the SDSS Data Release 5, we have extracted 11 163 groups at the linking length R0 = 0.2 × ¯ −1/3 = 1.97 Mpc by the three-dimensional friends-of-friends (FOF) algorithm, where ¯ n is the mean galaxy density, and compare basic properties of member galaxies of main galaxy groups with those of the main galaxy sample and isolated galaxies in each redshift bin. Results. The luminosities and sizes of galaxies are almost independent of environment, but morphologies and colors are correlated with environment-especially galaxy morphologies.

THE STATISTICAL PROPERTIES OF GALAXY MORPHOLOGICAL TYPES IN COMPACT GROUPS OF MAIN GALAXIES FROM THE SDSS DATA RELEASE 4

In order to explore the statistical properties of galaxy morphological types in compact groups (CGs), we construct a random group sample which has the same distributions of redshift and number of member galaxies as those of the CG sample. It turns out that the proportion of early-type galaxies in different redshift bins for the CG sample is statistically higher than that for random group sample, and with growing redshift z this kind of difference becomes more significant. This may be due to the existence of interactions and mergers within a significant fraction of SDSS CGs. We also compare statistical results of CGs with those of more compact groups and pairs, but do not observe as large statistical difference as Hicksons [Astrophys. J.255 (1982) 382] results.

The Properties of Isolated Main Galaxies in Sloan Digital Sky Survey Data Release 3 (SDSS DR3)

We have constructed a Main galaxy subsample of 67777 galaxies with redshifts in the range 0.08 ≤ z ≤ 0.12 from the Sloan Digital Sky Survey Data Release 3. Using cluster analysis, two isolated Main galaxy samples were extracted from this subsample. The two isolated Main galaxy samples identified at different radii have the same properties. Additionally, we find fewer early-type galaxies in isolated Main galaxy samples than in a close double galaxy sample.

Some Properties of Active Galactic Nuclei in the Volume-limited Main Galaxy Samples of SDSS DR8

Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 8 above and below the value of M* r , we have explored some properties of AGNs. In the luminous volume-limited sample, 9.5% is composite galaxies (C) and 5.0% AGNs, while in the faint volume-limited sample, these fractions are 7.2% and 2.9%, respectively. The C and AGN fractions increase with luminosity. We also note that the fraction of star-forming galaxies decreases with luminosity, but the fraction of low signal-to-noise star-forming galaxies slightly increases with luminosity. In two volume-limited samples, the fraction of star-forming galaxies decreases with density, while the AGN fraction is nearly insensitive to the local environment. If composite galaxies (C) are classified as AGNs, then the fraction of AGNs in the luminous volume-limited sample declines with increasing local density. When focusing on some properties of AGN host galaxies, we find that galaxies hosting AGNs are preferentially more massive and have high concentration indices. In the faint volume-limited sample, AGN host galaxies preferentially have low star formation rates (SFRs) and specific SFRs (SSFRs). However, in the luminous volume-limited sample, AGN host galaxies preferentially have moderate SFRs and SSFRs.

Environmental Dependence of Different Colors for the Apparent Magnitude-Limited Main Galaxy Sample of the SDSS DR7

Abstract The apparent magnitude-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 7 is used to investigate the environmental dependence of u–r, u–g, g–r, r–i and i–z colors. All the five colors strongly correlate with the local environment: red galaxies tend to be located in dense regions, while blue galaxies tend to be located in low density regions. We also note that with increasing of redshift, the environmental dependence of galaxy colors becomes weaker, especially in the high redshift region (z between 0.17 and 0.20). This can be explained accepting that subsamples with high redshifts contain only luminous and red galaxies.

THE DEPENDENCE OF LUMINOUS RED GALAXY (LRG) LUMINOSITY ON THE ENVIRONMENT

In order to investigate the dependence of LRG luminosity on the environment, we compare the luminosity distribution of member galaxies of LRG groups with that of isolated LRGs. It turns out that luminous LRGs exist preferentially in the densest regions of the universe (e.g. in groups), but faint LRGs are located preferentially in low density regions. The level of significance is above 2σ. This further confirms the dependence of galaxy luminosity on the environment.