Large quasar groups as a tool to study galaxy evolution

Quasars have been found to cluster generally on scales less than or equal to 10h(-1) Mpc. However, quasar clustering has also been observed on larger scales in the form of Large Quasar Groups (LQGs) (see Clowes 2001 and references therein). The LQGs-structures 100-200h(-1) Mpc in size, are possibly physical enhancements in the underlying mass density of the Universe, with the member quasars immersed in high-redshift counterparts of local structures such as the "Great Wall" of galaxies. This link between quasars and the large scale structure (LSS) of galaxies is consistent with the current view that the formation of quasars is closely related to the formation of galaxies, and with the recent finding that on the scales of superclusters (similar to 60h(-1) Mpc) low-z radio-quiet (z < 0.3) quasars follow the LSS traced by galaxy clusters.