The environmental dependence of galaxy properties for red early-types and red late-types

Abstract

Using the volume-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we intend to investigate the difference of the environmental dependence of galaxy properties between red early-types and red late-types. We measure the local three-dimensional galaxy density in a comoving sphere with a radius of the distance to the 5th nearest galaxy for each galaxy, construct two subsamples at both extremes of density for each sample, and compare the luminosity, g–r color and concentration index ci distributions in the lowest density regime with those in the densest regime. It is found that only in the luminosity range M r ⩽ −21.95 red early-type galaxies show the significant environmental dependence of luminosity, while in the red late-type sample the galaxy luminosity is nearly independent of environment. We note that the correlation between g–r color and environment for red late-types is much stronger than the one for red early-types, and that the strong environmental dependence of concentration index for red early-types and red late-types does not exist. We also measured the projected local density ∑ 5 which is computed from the distance to the 5th nearest neighbor within a redshift slice ±1000 km s −1 of each galaxy, and get the nearly same conclusions as the three-dimensional density. But the weak environmental dependence of luminosity and g–r color for red early-types, and concentration index for red late-types should be accepted with caution.