Toward understanding environmental effects in SDSS clusters

¹ Tartu Observatory, 61602 Tõravere, Estonia e-mail: einasto@aai.ee
² Tuorla Observatory, Väisäläntie 20, Piikkiö, Finland
³ Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str 1, 86740 Garching, FRG, Germany
⁴ Fermi National Accelerator Laboratory, MS 127, PO Box 500, Batavia, IL 60510, USA

Received: 9 November 2004
Accepted: 5 April 2005

Abstract

We find groups and clusters of galaxies using the Data Releases DR1 and DR3 of the Sloan Digital Sky Survey. We calculate a low-resolution density field with a smoothing length of 10 h^-1 Mpc to characterise the density of the cluster environment, and a medium-resolution density field with a smoothing length of 2 h^-1 Mpc to characterise the galaxy environment. We determine the luminosity function of clusters, and investigate properties of galaxies and clusters in various environments. We show that clusters in a high-density environment are about 5 times more luminous than in a low-density environment, and luminosities of galaxies in different environments differ by a factor of ∼25. We see similar effects in numerical simulations – simulated clusters in a high-density environment are ~ times more massive than those in a low-density environment. Comparison of the density distribution in simulations at various epochs shows that in large low-density regions (voids) dynamical evolution is very slow and stops early. 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.