Toward Understanding Environmental Effects in SDSS Clusters

J. Einasto, E. Tago, M. Einasto, E. Saar, I. Suhhonenko, P. Heinämäki, G. Hüetsi, D. L. Tucker

AA, submitted [astro-ph/0411235]

Paper in pdf format.

We find groups and clusters of galaxies using Data Releases DR1 and DR3 of the Sloan Digital Sky Survey. We calculate a low-resolution density field with a smoothing length of 10 Mpc to characterise the density of the cluster environment, and a medium-resolution density field with a smoothing length of 2 Mpc to characterize the galaxy environment. We determine the luminosity function of clusters, and investigate properties of clusters in various environments. We show that clusters in a high-density environment have a luminosity a factor of 5 higher than in a low-density environment, a similar contrast for luminosities of galaxies is by a factor of 25. We also study clusters in numerical simulations. Simulated clusters in a high-density environment are more massive than those in a low-density environment by a factor of 100. Comparison of the density distribution at various epochs in simulations shows that in large low-density regions (voids) dynamical evolution is very slow and stops at an early epoch. In contrast, in large regions of higher density (superclusters) dynamical evolution starts early and continues until the present; here particles cluster early, and by merging of smaller groups very rich systems of galaxies form.

Here we show the high resolution density field for the SDSS North and South, DR3:

Northern slice

Southern slice

 

Here are some animations showing the spatial distribution and movements of clusters in numerical simulations