Xiao-Xia Qian

Local Environmental Dependence of Galaxy Properties in a Volume-Limited Sample of Main Galaxies

Using a volume-limited sample of Main Galaxies from SDSS Data Release 5, we investigate the dependence of galaxy properties on local environment. For each galaxy, a local three-dimensional density is calculated. We find that the galaxy morphological type depends strongly on the local environment: galaxies in dense environments have predominantly early type morphologies. Galaxy colors have only a weak dependence on the environment. This puts an important constraint on the process of galaxy formation.

DEPENDENCE OF CLUSTERING ON GALAXY LUMINOSITY

From the flux-limited main galaxy sample of SDSS DR6, we construct three volume-limited samples with different luminosities, and compare clustering properties of three samples. We find that the luminosity dependence of clustering properties does not exhibit a single trend, which is different between the sample fainter than the characteristic luminosity M* of the Schechter luminosity function and those brighter than M*. In the galaxy samples brighter than M*, the brighter galaxies have a more concentrated and less filamentary distribution as compared to the fainter ones. But when performing comparative studies of the luminosity dependence of clustering properties between the sample fainter than M* and ones brighter than M*, an opposite trend is found.

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.

Luminosity-Environment Relation in the Lowz Sample of the SDSS-III

Abstract In this work, we examine the environmental dependence of the u-, g-, r-, i- and z-band luminosities in the LOWZ sample of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10). To decrease the radial selection effect, we divide the LOWZ sample into subsamples with a redshift bin size of Δz = 0.01 and analyze the environmental dependence of luminosities for these subsamples in each redshift bin. It is found that all five band luminosities of the LOWZ galaxy sample in the redshift region z=0.16–0.23 show substantial correlation with the local environment, especially in the redshift bins 0.19–0.20 and 0.20–0.21. The environmental dependence of all five band luminosities in the LOWZ galaxy sample becomes weak with increasing redshift, like the one in the apparent-magnitude limited Main galaxy sample.