SIMBAD references

From the volume-limited main galaxy sample of SDSS DR6, we extracted isolated galaxies and identified groups by different algorithms, in order to investigate the dependence of galaxy luminosity on environment. We compared the luminosity distributions of member galaxies of groups with that of isolated galaxies and the volume-limited main galaxy sample, and found that the luminosity distributions of member galaxies of groups are almost the same as that of the volume-limited sample, but are different from that of isolated galaxies: isolated galaxies have a higher proportion of faint galaxies (M_r≥-20.61) and a lower proportion of luminous galaxies (M_r≤-21.28) than member galaxies of groups. The level of significance is at least 3 σ. This shows that luminous galaxies exist preferentially in the densest regions of the universe (e.g., in groups), but faint galaxies are located preferentially in low-density regions. We also note that the dependence of galaxy luminosity on dense environment (e.g., in groups) is much weaker than that on underdense environment (e.g., isolated galaxies).