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

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 Mr ⩽ −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.